Reproduction and Development

Reproduction and Development
Chapter 26 Reproduction and Development

Biology and Society: Life after Death
Infertility is the inability to conceive after at least one year of trying and affects one in seven American couples. © 2013 Pearson Education, Inc. 2

Figure 26.0 Figure 26.0 Injection of donor sperm into a woman’s egg

An infertile couple in New Jersey were using reproductive technologies to try to become pregnant. But during those efforts, the husband suddenly died of a heart attack. Within 6 hours of the death of her husband, the woman requested that a sample of her late husband’s sperm be removed. © 2013 Pearson Education, Inc. 4

That sperm was used to fertilize the wife’s eggs and produce a child who is alive today. However, laws remain unclear regarding the rights of the child to death benefits. © 2013 Pearson Education, Inc. 5

UNIFYING CONCEPTS OF ANIMAL REPRODUCTION
Reproduction is the creation of new individuals from existing ones. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Many students expect that hermaphroditic animals fertilize themselves. Although this may be common in some animals, exchanging gametes between hermaphrodites also occurs, as noted in the text. 2. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. Teaching Tips 1. Aphid life cycles usually alternate between asexual and sexual reproductive strategies during a single year. Consider challenging your class to explain why aphids (and other animals) do this. In general, sexual reproduction is most common in times of stress, and may be related to overpopulation or environmental change in which diversity may be favored. 2. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base, which is in turn, attached to the substrate. The female moves over the spermatophore, removes some of the sperm from the cap, and stores the sperm in her reproductive tract until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. Many terrestrial salamander species use spermatophores, thus serving as one of the exceptions to the general rule that terrestrial animals reproduce by depositing sperm directly into the female’s body. 6

Asexual Reproduction Asexual reproduction
is reproduction without sex and creates offspring that are genetically identical to the parent. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Many students expect that hermaphroditic animals fertilize themselves. Although this may be common in some animals, exchanging gametes between hermaphrodites also occurs, as noted in the text. 2. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. Teaching Tips 1. Aphid life cycles usually alternate between asexual and sexual reproductive strategies during a single year. Consider challenging your class to explain why aphids (and other animals) do this. In general, sexual reproduction is most common in times of stress, and may be related to overpopulation or environmental change in which diversity may be favored. 2. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base, which is in turn, attached to the substrate. The female moves over the spermatophore, removes some of the sperm from the cap, and stores the sperm in her reproductive tract until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. Many terrestrial salamander species use spermatophores, thus serving as one of the exceptions to the general rule that terrestrial animals reproduce by depositing sperm directly into the female’s body 7

Asexual Reproduction Budding is a type of asexual reproduction and
produces offspring by the outgrowth and eventual splitting off of a new individual from the parent. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Many students expect that hermaphroditic animals fertilize themselves. Although this may be common in some animals, exchanging gametes between hermaphrodites also occurs, as noted in the text. 2. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. Teaching Tips 1. Aphid life cycles usually alternate between asexual and sexual reproductive strategies during a single year. Consider challenging your class to explain why aphids (and other animals) do this. In general, sexual reproduction is most common in times of stress, and may be related to overpopulation or environmental change in which diversity may be favored. 2. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base, which is in turn, attached to the substrate. The female moves over the spermatophore, removes some of the sperm from the cap, and stores the sperm in her reproductive tract until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. Many terrestrial salamander species use spermatophores, thus serving as one of the exceptions to the general rule that terrestrial animals reproduce by depositing sperm directly into the female’s body 8

Figure 26.1 Bud Figure 26.1 Asexual reproduction via budding in a hydra

Asexual Reproduction During the asexual process of fission, a parent separates into two or more offspring of about equal size. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Many students expect that hermaphroditic animals fertilize themselves. Although this may be common in some animals, exchanging gametes between hermaphrodites also occurs, as noted in the text. 2. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. Teaching Tips 1. Aphid life cycles usually alternate between asexual and sexual reproductive strategies during a single year. Consider challenging your class to explain why aphids (and other animals) do this. In general, sexual reproduction is most common in times of stress, and may be related to overpopulation or environmental change in which diversity may be favored. 2. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base, which is in turn, attached to the substrate. The female moves over the spermatophore, removes some of the sperm from the cap, and stores the sperm in her reproductive tract until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. Many terrestrial salamander species use spermatophores, thus serving as one of the exceptions to the general rule that terrestrial animals reproduce by depositing sperm directly into the female’s body 10

Figure 26.2 Figure 26.2 Asexual reproduction via fission in a sea anemone

Asexual Reproduction Fragmentation is the breaking of a parent body into several pieces. Regeneration typically follows fragmentation and is the regrowth of lost body parts. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Many students expect that hermaphroditic animals fertilize themselves. Although this may be common in some animals, exchanging gametes between hermaphrodites also occurs, as noted in the text. 2. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. Teaching Tips 1. Aphid life cycles usually alternate between asexual and sexual reproductive strategies during a single year. Consider challenging your class to explain why aphids (and other animals) do this. In general, sexual reproduction is most common in times of stress, and may be related to overpopulation or environmental change in which diversity may be favored. 2. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base, which is in turn, attached to the substrate. The female moves over the spermatophore, removes some of the sperm from the cap, and stores the sperm in her reproductive tract until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. Many terrestrial salamander species use spermatophores, thus serving as one of the exceptions to the general rule that terrestrial animals reproduce by depositing sperm directly into the female’s body 12

Asexual Reproduction Asexual reproduction
eliminates the need to find a mate, allows a population to perpetuate itself if its individual members are isolated from one another, and permits organisms to multiply quickly without spending time or energy producing sperm and eggs. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Many students expect that hermaphroditic animals fertilize themselves. Although this may be common in some animals, exchanging gametes between hermaphrodites also occurs, as noted in the text. 2. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. Teaching Tips 1. Aphid life cycles usually alternate between asexual and sexual reproductive strategies during a single year. Consider challenging your class to explain why aphids (and other animals) do this. In general, sexual reproduction is most common in times of stress, and may be related to overpopulation or environmental change in which diversity may be favored. 2. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base, which is in turn, attached to the substrate. The female moves over the spermatophore, removes some of the sperm from the cap, and stores the sperm in her reproductive tract until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. Many terrestrial salamander species use spermatophores, thus serving as one of the exceptions to the general rule that terrestrial animals reproduce by depositing sperm directly into the female’s body 13

Asexual Reproduction However, asexual reproduction produces genetically identical offspring, which limits a population’s chances of surviving periods of environmental change. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Many students expect that hermaphroditic animals fertilize themselves. Although this may be common in some animals, exchanging gametes between hermaphrodites also occurs, as noted in the text. 2. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. Teaching Tips 1. Aphid life cycles usually alternate between asexual and sexual reproductive strategies during a single year. Consider challenging your class to explain why aphids (and other animals) do this. In general, sexual reproduction is most common in times of stress, and may be related to overpopulation or environmental change in which diversity may be favored. 2. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base, which is in turn, attached to the substrate. The female moves over the spermatophore, removes some of the sperm from the cap, and stores the sperm in her reproductive tract until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. Many terrestrial salamander species use spermatophores, thus serving as one of the exceptions to the general rule that terrestrial animals reproduce by depositing sperm directly into the female’s body 14

Sexual Reproduction Sexual reproduction involves the
fusion of two haploid sex cells called gametes (sperm and egg) and formation of a diploid zygote. Sexual reproduction increases the genetic variability among offspring and chances that some of the varying offspring will survive and reproduce. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Many students expect that hermaphroditic animals fertilize themselves. Although this may be common in some animals, exchanging gametes between hermaphrodites also occurs, as noted in the text. 2. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. Teaching Tips 1. Aphid life cycles usually alternate between asexual and sexual reproductive strategies during a single year. Consider challenging your class to explain why aphids (and other animals) do this. In general, sexual reproduction is most common in times of stress, and may be related to overpopulation or environmental change in which diversity may be favored. 2. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base, which is in turn, attached to the substrate. The female moves over the spermatophore, removes some of the sperm from the cap, and stores the sperm in her reproductive tract until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. Many terrestrial salamander species use spermatophores, thus serving as one of the exceptions to the general rule that terrestrial animals reproduce by depositing sperm directly into the female’s body 15

Sexual Reproduction Some animals can reproduce sexually and asexually.
© 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Many students expect that hermaphroditic animals fertilize themselves. Although this may be common in some animals, exchanging gametes between hermaphrodites also occurs, as noted in the text. 2. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. Teaching Tips 1. Aphid life cycles usually alternate between asexual and sexual reproductive strategies during a single year. Consider challenging your class to explain why aphids (and other animals) do this. In general, sexual reproduction is most common in times of stress, and may be related to overpopulation or environmental change in which diversity may be favored. 2. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base, which is in turn, attached to the substrate. The female moves over the spermatophore, removes some of the sperm from the cap, and stores the sperm in her reproductive tract until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. Many terrestrial salamander species use spermatophores, thus serving as one of the exceptions to the general rule that terrestrial animals reproduce by depositing sperm directly into the female’s body 16

Sexual Reproduction In some species, each individual is a hermaphrodite, with male and female reproductive systems. Some hermaphrodites can fertilize their own eggs, while other species require a partner. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Many students expect that hermaphroditic animals fertilize themselves. Although this may be common in some animals, exchanging gametes between hermaphrodites also occurs, as noted in the text. 2. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. Teaching Tips 1. Aphid life cycles usually alternate between asexual and sexual reproductive strategies during a single year. Consider challenging your class to explain why aphids (and other animals) do this. In general, sexual reproduction is most common in times of stress, and may be related to overpopulation or environmental change in which diversity may be favored. 2. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base, which is in turn, attached to the substrate. The female moves over the spermatophore, removes some of the sperm from the cap, and stores the sperm in her reproductive tract until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. Many terrestrial salamander species use spermatophores, thus serving as one of the exceptions to the general rule that terrestrial animals reproduce by depositing sperm directly into the female’s body 17

Sexual Reproduction The mechanics of fertilization play an important part in sexual reproduction. Many aquatic animals use external fertilization and discharge their gametes into the water. In nearly all terrestrial animals, males deposit sperm directly into the female body. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Many students expect that hermaphroditic animals fertilize themselves. Although this may be common in some animals, exchanging gametes between hermaphrodites also occurs, as noted in the text. 2. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. Teaching Tips 1. Aphid life cycles usually alternate between asexual and sexual reproductive strategies during a single year. Consider challenging your class to explain why aphids (and other animals) do this. In general, sexual reproduction is most common in times of stress, and may be related to overpopulation or environmental change in which diversity may be favored. 2. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base, which is in turn, attached to the substrate. The female moves over the spermatophore, removes some of the sperm from the cap, and stores the sperm in her reproductive tract until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. Many terrestrial salamander species use spermatophores, thus serving as one of the exceptions to the general rule that terrestrial animals reproduce by depositing sperm directly into the female’s body 18

Figure 26.4 Egg Figure 26.4 External fertilization in frogs

HUMAN REPRODUCTION Both sexes of humans have
a pair of gonads that produce gametes, ducts to store and deliver the gametes, and structures that allow mating. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 20

Male Reproductive Anatomy
The penis contains erectile tissue that fills with blood and becomes erect during sexual arousal. A prepuce, or foreskin, covers the glans and may be removed surgically in a procedure known as circumcision. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 21

The male gonads, the testes, are enclosed in a sac called the scrotum and produce sperm. A testis and scrotum together are called a testicle. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 22

By keeping the sperm-forming cells away from the body, the scrotum keeps the testes cool enough for sperm to develop normally. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 23

Side view Rectum Seminal vesicle Urinary bladder Vas deferens
Figure 26.5a Side view Rectum Seminal vesicle Urinary bladder Vas deferens Pubic bone Sperm duct Erectile tissue Prostate gland Urethra Vas deferens Penis Anus Epididymis Glans Testis Testicle Prepuce Scrotum Figure 26.5 The male reproductive system: side (part 1)

During ejaculation, sperm leave the epididymis and travel through a duct called the vas deferens. The seminal vesicles and prostate gland add fluid that nourishes the sperm and provides protection from the natural acidity of the vagina. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 25

Semen consists of these glandular fluids and sperm. The urethra conveys through the penis, at different times, both semen and urine. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 26

Front view Urinary bladder Seminal vesicle (behind bladder)
Figure 26.5b Front view Urinary bladder Seminal vesicle (behind bladder) Prostate gland Erectile tissue of penis Urethra Vas deferens Epididymis Glans of penis Testis Scrotum Testicle Figure 26.5 The male reproductive system: front (part 2)

Female Reproductive Anatomy
The outer features of the female reproductive tract are collectively called the vulva and consist of the vagina, or birth canal, the labia majora, fatty ridges that protect the entire genital region, © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 28

the labia minora, inner folds bordering the openings, the hymen, partially covering the vaginal opening, and the clitoris, which becomes erect upon sexual arousal. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 29

Ovaries Oviduct Follicles Uterus Front view Corpus luteum Endometrium
Figure 26.6 Ovaries Oviduct Follicles Uterus Front view Corpus luteum Endometrium (lining of uterus) Wall of uterus Cervix (“neck” of uterus) Vagina Oviduct Ovary Uterus Side view Urinary bladder Rectum Pubic bone Cervix Urethra Shaft Vagina Glans Clitoris Prepuce Vulva Labia minora Anus Vaginal opening Labia majora Figure 26.6 The female reproductive system

Oviduct Side view Ovary Uterus Urinary bladder Rectum Pubic bone
Figure 26.6a Oviduct Side view Ovary Uterus Urinary bladder Rectum Pubic bone Cervix Urethra Shaft Vagina Glans Clitoris Prepuce Vulva Labia minora Anus Labia majora Vaginal opening Figure 26.6 The female reproductive system: side (part 1)

The ovaries are the sites of gamete production and contain follicles consisting of a single egg surrounded by cells that nourish and protect it. The follicles also produce estrogen, the female sex hormone. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 32

During ovulation, an immature egg is ejected from a follicle and enters the oviduct, where fertilization typically occurs. The remains of the follicle grow to form a solid mass, the corpus luteum, which secretes hormones during the reproductive cycle. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 33

Ovaries Oviduct Follicles Uterus Front view Corpus luteum Endometrium
Figure 26.6b Ovaries Oviduct Follicles Uterus Front view Corpus luteum Endometrium (lining of uterus) Wall of uterus Cervix (“neck” of uterus) Vagina Figure 26.6 The female reproductive system: front (part 2)

The uterus is the actual site of pregnancy and lined by a thick blood-rich layer of tissue, the endometrium, where an embryo implants and grows. A developing human is called an embryo for the first nine weeks and a fetus from the 9th week until birth. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 35

The cervix is the narrow neck at the bottom of the pear-shaped uterus and opens into the vagina. Annual Pap smears sample cervical cells and can detect cervical cancer early, when treatment is more likely to be successful © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 36

Gametogenesis Gametogenesis Humans have uses meiosis and
produces haploid cells called gametes. Humans have diploid cells with 46 chromosomes and haploid gametes with 23 chromosomes. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 37

Primary spermatocytes
Spermatogenesis Spermatogenesis is the formation of sperm cells and occurs in seminiferous tubules inside the testes. Primary spermatocytes are diploid cells, undergo meiosis I, and produce secondary spermatocytes. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 38

Spermatogenesis Secondary spermatocytes undergo meiosis II, each with the haploid number of chromosomes. Thus, spermatogenesis produces a total of four haploid cells from each primary spermatocyte. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 39

Secondary spermatocyte (haploid) Meiosis II
Figure 26.7 Epididymis Penis Testis Scrotum 2n Diploid cell Differentiation and onset of meiosis I Testis Seminiferous tubule Cross section of seminiferous tubule 2n Primary spermatocyte (diploid) Meiosis I completed n n Secondary spermatocyte (haploid) Meiosis II n n n n Developing sperm cells Cellular differentiation (cells become specialized) Sperm cells n n n n (haploid) Mature sperm released into center of seminiferous tubule Figure 26.7 Spermatogenesis

Epididymis Penis Testis Scrotum Testis Seminiferous tubule
Figure 26.7a Epididymis Penis Testis Scrotum Testis Seminiferous tubule Cross section of seminiferous tubule Figure 26.7 Spermatogenesis (part 1)

Secondary spermatocyte
Figure 26.7b-5 2n Diploid cell Differentiation and onset of meiosis I Primary spermatocyte 2n (diploid) Meiosis I completed Secondary spermatocyte n n (haploid) Meiosis II n n n n Developing sperm cells Cellular differentiation (cells become specialized) Sperm cells n n n n (haploid) Mature sperm released into center of seminiferous tubule Figure 26.7 Spermatogenesis (part 2, step 5)

Oogenesis is the development of eggs within the ovaries.
A primary oocyte is a diploid cell that pauses during prophase of meiosis I and can be triggered to develop further by the hormone FSH to produce a secondary oocyte and a small polar body with almost no cytoplasm. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 43

Oogenesis Meiosis II produces a mature ovum and another polar body. 44
© 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 44

Figure 26.8 Oogenesis and development of an ovarian follicle
Primary oocyte within follicle Growing follicle Before birth 2n Diploid cell in embryo Secondary oocyte Mature follicle Ovary Differentiation and onset of meiosis I Ruptured follicle 2n Primary oocyte (diploid) arrested at prophase of meiosis I; present at birth Completion of meiosis I and onset of meiosis II Ovulated secondary oocyte First polar body n LM A secondary oocyte being released during ovulation n Secondary oocyte (haploid) arrested at metaphase of meiosis II Entry of sperm triggers completion of meiosis II Corpus luteum n Second polar body Mature egg (ovum) n Degenerating corpus luteum (haploid) Figure 26.8 Oogenesis and development of an ovarian follicle

Primary oocyte within follicle Figure 26.8a
Figure 26.8 Oogenesis and development of an ovarian follicle (part 1)

Differentiation and onset of meiosis I
Figure 26.8b-1 Before birth Primary oocyte within follicle 2n Diploid cell in embryo Differentiation and onset of meiosis I 2n Primary oocyte (diploid) arrested at prophase of meiosis I; present at birth Figure 26.8 Oogenesis and development of an ovarian follicle (part 2, step 1)

Differentiation and onset of meiosis I Growing follicle
Figure 26.8b-2 Before birth Primary oocyte within follicle 2n Diploid cell in embryo Differentiation and onset of meiosis I Growing follicle 2n Primary oocyte (diploid) arrested at prophase of meiosis I; present at birth Mature follicle Completion of meiosis I and onset of meiosis II First polar body n n Secondary oocyte (haploid) arrested at metaphase of meiosis II Figure 26.8 Oogenesis and development of an ovarian follicle (part 2, step 2)

Figure 26.8b-3 Before birth Primary oocyte within follicle 2n Diploid cell in embryo Differentiation and onset of meiosis I Growing follicle 2n Primary oocyte (diploid) arrested at prophase of meiosis I; present at birth Mature follicle Completion of meiosis I and onset of meiosis II First polar body n n Secondary oocyte (haploid) arrested at metaphase of meiosis II Ruptured follicle Ovulated secondary oocyte Figure 26.8 Oogenesis and development of an ovarian follicle (part 2, step 3)

Figure 26.8b-4 Before birth Primary oocyte within follicle 2n Diploid cell in embryo Differentiation and onset of meiosis I Growing follicle 2n Primary oocyte (diploid) arrested at prophase of meiosis I; present at birth Mature follicle Completion of meiosis I and onset of meiosis II First polar body n n Secondary oocyte (haploid) Entry of sperm triggers completion of meiosis II arrested at metaphase of meiosis II Ruptured follicle Second polar body n Ovulated secondary oocyte Mature egg (ovum) n (haploid) Figure 26.8 Oogenesis and development of an ovarian follicle (part 2, step 4)

Ovulated secondary oocyte
Figure 26.8c Secondary oocyte Ovary Ruptured follicle Ovulated secondary oocyte LM A secondary oocyte being released during ovulation Corpus luteum Degenerating corpus luteum Figure 26.8 Oogenesis and development of an ovarian follicle (part 3)

Oogenesis Both oogenesis and spermatogenesis produce haploid gametes, but there are several important differences. Human males create new sperm every day, from puberty through old age. Human females create primary oocytes only during fetal development. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 52

Oogenesis Spermatogenesis produces four gametes from each diploid parent cell, but oogenesis produces only one gamete from each diploid parent cell. Sperm are small and motile, while eggs are large and nonmotile. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 53

The Female Reproductive Cycle
Human females have a reproductive cycle, a recurring series of events that produces gametes, makes eggs available for fertilization, and prepares the body for pregnancy. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 54

The female reproductive cycle is actually two cycles in one: the ovarian cycle controls the growth and release of an egg and the menstrual (uterine) cycle prepares the uterus for possible implantation of an embryo. Hormonal messages coordinate the ovarian and menstrual cycles. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 55

Menstruation is uterine bleeding caused by the breakdown of the endometrium. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Student background knowledge of human reproductive biology is likely quite uneven. What is well understood by some students is new to others. Further, the embarrassment frequently associated with related topics makes it difficult for teachers to fairly assess what students know. The best advice may be to not assume too much. 2. Student embarrassment with the subject of human reproductive biology may make open discussions uncomfortable for some students. Good clear textbook and media assignments that can be studied privately and opportunities to ask anonymous questions provide additional avenues to address sensitive content and questions. Teaching Tips 1. Endometriosis is an inflammatory condition in which the endometrium spreads beyond the uterus. It can lead to painful menstrual cycles and infertility. The Endometriosis Association website is a good resource for additional information. 2. Men in your class will be well aware of physiological changes in the scrotum associated with thermoregulation. When a man enters into cool water, the scrotum is pulled tight and the testes are held close to the body. During a warm shower or bath, the scrotum relaxes and the testes are held far away from the body. Women in your class may be much less aware of this common phenomenon. 3. In class, on a quiz, or on an exam, ask students to explain why polar bodies are produced at all, and why they have so little cytoplasm. Challenge them to explain why polar bodies are not produced in spermatogenesis. (In general, oogenesis conserves cytoplasm while reducing the genetic composition of the forming ovum.) 4. Testicular cancer is the most common form of cancer in men between 15 and 35 years of age. Students can find information about testicular cancer and how to perform a self-exam at the website for the American Cancer Society at 5. Students might wonder why a woman’s body goes through menstrual cycles. Why not just sustain the endometrium continuously? One hypothesis suggests that because the uterus is a good environment in which bacteria can grow, menstrual cycles are a way to “flush” the system and discourage microbial growth. 6. Many home pregnancy tests rely upon antibodies to HCG. 7. The Sexuality Information and Education Council of the United States (SIECUS) is a national, nonprofit organization, which affirms that sexuality is a natural and healthy part of living. Its website, at is an excellent source of information related to this chapter. 56

Control by hypothalamus
Figure 26.9ab (a) Control by hypothalamus Inhibited by combination of estrogen and progesterone Hypothalamus Stimulated by high levels of estrogen Releasing hormone Anterior pituitary 1 FSH LH (b) Levels of pituitary hormones in blood 4 LH FSH 2 FSH stimulates follicle to grow LH peak triggers ovulation 5 10 14 15 20 25 28 Days Figure 26.9 The reproductive cycle of the human female (part 1)

Degenerating corpus luteum
Figure 26.9bc (b) Levels of pituitary hormones in blood 4 LH FSH 2 FSH stimulates follicle to grow LH peak triggers ovulation (c) Ovarian cycle 5 Corpus luteum Degenerating corpus luteum Growing follicle Mature follicle Ovulation Estrogen secreted by growing follicle Progesterone and estrogen secreted by remnant of follicle 5 10 14 15 20 25 28 Days Figure 26.9 The reproductive cycle of the human female (part 2)

Degenerating corpus luteum
Figure 26.9cd (c) Ovarian cycle 5 Corpus luteum Degenerating corpus luteum Growing follicle Mature follicle Ovulation Estrogen secreted by growing follicle Progesterone and estrogen secreted by remnant of follicle (d) Levels of ovarian hormones in blood Peak causes LH surge 3 6 7 Estrogen Progesterone Low levels trigger menstruation Progesterone and estrogen promote thickening of endometrium 5 10 14 15 20 25 28 Days Figure 26.9 The reproductive cycle of the human female (part 3)

Levels of ovarian hormones in blood
Figure 26.9de (d) Levels of ovarian hormones in blood Peak causes LH surge 3 6 7 Estrogen Progesterone Low levels trigger menstruation Progesterone and estrogen promote thickening of endometrium (e) Menstrual cycle Endometrium 5 10 14 15 20 25 28 Days Figure 26.9 The reproductive cycle of the human female (part 4)

REPRODUCTIVE HEALTH Two issues of human reproductive health are
contraception, the deliberate prevention of pregnancy, and sexually transmitted diseases (STDs). © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly equate contraception with prevention of sexually transmitted diseases. As you review the forms of birth control, consider pointing out the strategies that provide little or no protection against STDs. The pill, for example, does nothing to prevent disease transmission. Consider noting that methods that greatly reduce the transmission of disease (condoms used with spermicides) are also effective forms of birth control. 2. Students often expect that drugs are available to cure most or all STDs. However, viral infections should be considered lifelong diseases. HIV, herpes, and HPV are examples of such STD viruses. Teaching Tips 1. Although people infected with sexually transmitted diseases might have no apparent symptoms, they may still be capable of infecting partners. This important point is worth repeating to young college audiences who may be overly optimistic about the health of their partners. 2. Chlamydia is the most frequently reported bacterial STD in the United States (Source: CDC fact sheet at 61

Contraception Contraception comes in many forms with varying degrees of effectiveness. Complete abstinence (avoiding intercourse) is the only totally effective method of contraception. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly equate contraception with prevention of sexually transmitted diseases. As you review the forms of birth control, consider pointing out the strategies that provide little or no protection against STDs. The pill, for example, does nothing to prevent disease transmission. Consider noting that methods that greatly reduce the transmission of disease (condoms used with spermicides) are also effective forms of birth control. 2. Students often expect that drugs are available to cure most or all STDs. However, viral infections should be considered lifelong diseases. HIV, herpes, and HPV are examples of such STD viruses. Teaching Tips 1. Although people infected with sexually transmitted diseases might have no apparent symptoms, they may still be capable of infecting partners. This important point is worth repeating to young college audiences who may be overly optimistic about the health of their partners. 2. Chlamydia is the most frequently reported bacterial STD in the United States (Source: CDC fact sheet at 62

Contraception Sterilization surgery prevents sperm from reaching an egg and is very reliable. The oviducts are cut and often tied off in a tubal ligation. The vas deferens are cut, preventing sperm from reaching the urethra, in a vasectomy. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly equate contraception with prevention of sexually transmitted diseases. As you review the forms of birth control, consider pointing out the strategies that provide little or no protection against STDs. The pill, for example, does nothing to prevent disease transmission. Consider noting that methods that greatly reduce the transmission of disease (condoms used with spermicides) are also effective forms of birth control. 2. Students often expect that drugs are available to cure most or all STDs. However, viral infections should be considered lifelong diseases. HIV, herpes, and HPV are examples of such STD viruses. Teaching Tips 1. Although people infected with sexually transmitted diseases might have no apparent symptoms, they may still be capable of infecting partners. This important point is worth repeating to young college audiences who may be overly optimistic about the health of their partners. 2. Chlamydia is the most frequently reported bacterial STD in the United States (Source: CDC fact sheet at 63

Table 26.1 Table 26.1 Contraceptive methods

Contraception Temporary abstinence
is also called the rhythm method or natural family planning and depends on refraining from intercourse during the days around ovulation. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly equate contraception with prevention of sexually transmitted diseases. As you review the forms of birth control, consider pointing out the strategies that provide little or no protection against STDs. The pill, for example, does nothing to prevent disease transmission. Consider noting that methods that greatly reduce the transmission of disease (condoms used with spermicides) are also effective forms of birth control. 2. Students often expect that drugs are available to cure most or all STDs. However, viral infections should be considered lifelong diseases. HIV, herpes, and HPV are examples of such STD viruses. Teaching Tips 1. Although people infected with sexually transmitted diseases might have no apparent symptoms, they may still be capable of infecting partners. This important point is worth repeating to young college audiences who may be overly optimistic about the health of their partners. 2. Chlamydia is the most frequently reported bacterial STD in the United States (Source: CDC fact sheet at 65

Contraception Barrier methods prevent sperm from meeting an egg. These include diaphragms, dome-shaped rubber caps that cover the cervix, and condoms, sheaths usually made of latex, that fit over the penis or within the vagina. Barrier devices are usually used with spermicides, sperm-killing chemicals. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly equate contraception with prevention of sexually transmitted diseases. As you review the forms of birth control, consider pointing out the strategies that provide little or no protection against STDs. The pill, for example, does nothing to prevent disease transmission. Consider noting that methods that greatly reduce the transmission of disease (condoms used with spermicides) are also effective forms of birth control. 2. Students often expect that drugs are available to cure most or all STDs. However, viral infections should be considered lifelong diseases. HIV, herpes, and HPV are examples of such STD viruses. Teaching Tips 1. Although people infected with sexually transmitted diseases might have no apparent symptoms, they may still be capable of infecting partners. This important point is worth repeating to young college audiences who may be overly optimistic about the health of their partners. 2. Chlamydia is the most frequently reported bacterial STD in the United States (Source: CDC fact sheet at 66

Contraception Birth control hormones include
oral contraceptives, or birth control pills, morning-after pills (MAPs), which are about 75% effective at preventing pregnancy when taken within three days of intercourse, and RU-486, which can induce an abortion. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly equate contraception with prevention of sexually transmitted diseases. As you review the forms of birth control, consider pointing out the strategies that provide little or no protection against STDs. The pill, for example, does nothing to prevent disease transmission. Consider noting that methods that greatly reduce the transmission of disease (condoms used with spermicides) are also effective forms of birth control. 2. Students often expect that drugs are available to cure most or all STDs. However, viral infections should be considered lifelong diseases. HIV, herpes, and HPV are examples of such STD viruses. Teaching Tips 1. Although people infected with sexually transmitted diseases might have no apparent symptoms, they may still be capable of infecting partners. This important point is worth repeating to young college audiences who may be overly optimistic about the health of their partners. 2. Chlamydia is the most frequently reported bacterial STD in the United States (Source: CDC fact sheet at 67

Sexually Transmitted Diseases
Sexually transmitted diseases (STDs) are contagious diseases and spread by sexual contact. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly equate contraception with prevention of sexually transmitted diseases. As you review the forms of birth control, consider pointing out the strategies that provide little or no protection against STDs. The pill, for example, does nothing to prevent disease transmission. Consider noting that methods that greatly reduce the transmission of disease (condoms used with spermicides) are also effective forms of birth control. 2. Students often expect that drugs are available to cure most or all STDs. However, viral infections should be considered lifelong diseases. HIV, herpes, and HPV are examples of such STD viruses. Teaching Tips 1. Although people infected with sexually transmitted diseases might have no apparent symptoms, they may still be capable of infecting partners. This important point is worth repeating to young college audiences who may be overly optimistic about the health of their partners. 2. Chlamydia is the most frequently reported bacterial STD in the United States (Source: CDC fact sheet at 68

Viral STDs cannot be cured but can be controlled by medications and include AIDS, genital herpes, and genital warts. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly equate contraception with prevention of sexually transmitted diseases. As you review the forms of birth control, consider pointing out the strategies that provide little or no protection against STDs. The pill, for example, does nothing to prevent disease transmission. Consider noting that methods that greatly reduce the transmission of disease (condoms used with spermicides) are also effective forms of birth control. 2. Students often expect that drugs are available to cure most or all STDs. However, viral infections should be considered lifelong diseases. HIV, herpes, and HPV are examples of such STD viruses. Teaching Tips 1. Although people infected with sexually transmitted diseases might have no apparent symptoms, they may still be capable of infecting partners. This important point is worth repeating to young college audiences who may be overly optimistic about the health of their partners. 2. Chlamydia is the most frequently reported bacterial STD in the United States (Source: CDC fact sheet at 69

Herpes simplex virus Colorized TEM Figure 26.UN04
Figure 26.UN04 In-text figure, Herpes simplex virus, p. 561

Papillomaviruses Colorized TEM Figure 26.UN05
Figure 26.UN05 In-text figure, Papillomaviruses, p. 561

STDs caused by bacteria, protozoans, and fungi are generally curable with drugs. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly equate contraception with prevention of sexually transmitted diseases. As you review the forms of birth control, consider pointing out the strategies that provide little or no protection against STDs. The pill, for example, does nothing to prevent disease transmission. Consider noting that methods that greatly reduce the transmission of disease (condoms used with spermicides) are also effective forms of birth control. 2. Students often expect that drugs are available to cure most or all STDs. However, viral infections should be considered lifelong diseases. HIV, herpes, and HPV are examples of such STD viruses. Teaching Tips 1. Although people infected with sexually transmitted diseases might have no apparent symptoms, they may still be capable of infecting partners. This important point is worth repeating to young college audiences who may be overly optimistic about the health of their partners. 2. Chlamydia is the most frequently reported bacterial STD in the United States (Source: CDC fact sheet at 72

Chlamydia is the most common bacterial STD in the United States, poses a public health challenge because it is frequently “silent,” producing no visible symptoms, may lead to pelvic inflammatory disease (PID) and infertility, and can be easily treated with a single dose of an antibiotic. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly equate contraception with prevention of sexually transmitted diseases. As you review the forms of birth control, consider pointing out the strategies that provide little or no protection against STDs. The pill, for example, does nothing to prevent disease transmission. Consider noting that methods that greatly reduce the transmission of disease (condoms used with spermicides) are also effective forms of birth control. 2. Students often expect that drugs are available to cure most or all STDs. However, viral infections should be considered lifelong diseases. HIV, herpes, and HPV are examples of such STD viruses. Teaching Tips 1. Although people infected with sexually transmitted diseases might have no apparent symptoms, they may still be capable of infecting partners. This important point is worth repeating to young college audiences who may be overly optimistic about the health of their partners. 2. Chlamydia is the most frequently reported bacterial STD in the United States (Source: CDC fact sheet at 73

Chlamydia trachomatis
Figure 26.UN01 Colorized TEM Chlamydia trachomatis Figure 26.UN01 In-text figure, Chlamydia trachomatis, p. 561

Trichomonas vaginalis
Figure 26.UN06 Colorized SEM Trichomonas vaginalis Figure 26.UN06 In-text figure, Trichomonas vaginalis, p. 561

Candida albicans Colorized SEM Figure 26.UN07
Figure 26.UN07 In-text figure, Candida albicans, p. 561

Table 26.2 STDs common in the United States (with micrographs)
Table 26.2a Colorized TEM Colorized TEM Colorized SEM Colorized TEM Chlamydia trachomatis Neisseria gonorrhoeae Treponema pallidum Herpes simplex virus Colorized TEM Papillomaviruses Colorized SEM Trichomonas vaginalis Colorized SEM Candida albicans Table 26.2 STDs common in the United States (with micrographs)

HUMAN DEVELOPMENT Embryonic development begins with fertilization, the union of sperm and egg to form a zygote. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think that fetal blood and mother’s blood run together, one into the other. Few students typically have a good understanding of the relationship of fetal and maternal blood in the placenta. 2. The extraembryonic membranes surrounding a human embryo are also not well understood by college students outside of the health sciences. These extraembryonic membranes can be viewed as analogous to the life-support systems used by astronauts. Teaching Tips 1. Gastrulation establishes the basic body plan by positioning the future systems of the body in relationship to each other. This essential element of gastrulation is a crucial event that is a prerequisite for later developmental events (and thus is the basis of the quote directly below). 2. You might wish to reflect on the somewhat famous quote of Lewis Wolpert, who in 1986 said, “It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.” The development and arrangement of the basic embryonic layers (ectoderm: skin and nervous system; mesoderm: muscle and bone; and endoderm: digestive tract) establishes the basic body plan. 3. Ectopic pregnancies occur when an embryo implants anywhere other than the uterus. Most frequently, ectopic pregnancies occur in the oviducts. However, the structure of the oviduct cannot accommodate the growth of a fetus. Surgical removal of the ectopic pregnancy, resulting in an abortion, is thus required for the sake of the mother’s health. In the ongoing political and ethical debate about abortion, this circumstance is often noted as an acceptable exception, “to save the life of the mother.” 4. Programmed cell death in the formation of human hands is like carving. One begins with more “material” than is necessary and removes what is not needed to reveal the final shape. 5. All vertebrates develop in a fluid environment. Fish and amphibians typically lay their eggs in water. Amniotes (reptiles, birds, and mammals) are defined by the presence of an amniotic sac, a self-contained aquatic system that surrounds the embryo with water inside the egg. The evolution of the amniotic egg removed the need to reproduce near water, freeing amniotes to reproduce underground, in deserts, and in trees! 6. Morning sickness typically occurs during the first trimester and subsides during the second. However, a great deal of variation in the timing and degree of symptoms is known. Unfortunately, the precise cause of morning sickness remains unknown. 7. Most human babies weigh 3–4 kilograms (kg) at birth. Birth weights much larger or smaller than this are associated with increased mortality. This is an example of stabilizing selection, discussed in Chapter 13. 8. When discussing the dilation of the cervix as part of labor, it might be useful to note that cigarettes are 90–100 mm long. Thus, a fully dilated cervix is about as wide as a cigarette is long. 9. The descriptions of basic development address questions that students may have never thought to ask. How do we get so many cells (trillions!) in our adult bodies? How do basic tissues, organs, and organ systems form? What mechanisms permit the coordinated development of the body? Before beginning this chapter, consider challenging your students with some of these fundamental questions: How did you get a heart, a brain, and ears? What determined when you were ready to be born? How did you get nutrients and oxygen before you could eat or breathe? 10. The many benefits of breastfeeding are noted at the web site of the U.S. Dept. of Health and Human Services, which can be found at 78

Fertilization Sexual intercourse releases hundreds of millions of sperm into the vagina, but only a few thousand sperm survive the trip to the egg and only one will fertilize it. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think that fetal blood and mother’s blood run together, one into the other. Few students typically have a good understanding of the relationship of fetal and maternal blood in the placenta. 2. The extraembryonic membranes surrounding a human embryo are also not well understood by college students outside of the health sciences. These extraembryonic membranes can be viewed as analogous to the life-support systems used by astronauts. Teaching Tips 1. Gastrulation establishes the basic body plan by positioning the future systems of the body in relationship to each other. This essential element of gastrulation is a crucial event that is a prerequisite for later developmental events (and thus is the basis of the quote directly below). 2. You might wish to reflect on the somewhat famous quote of Lewis Wolpert, who in 1986 said, “It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.” The development and arrangement of the basic embryonic layers (ectoderm: skin and nervous system; mesoderm: muscle and bone; and endoderm: digestive tract) establishes the basic body plan. 3. Ectopic pregnancies occur when an embryo implants anywhere other than the uterus. Most frequently, ectopic pregnancies occur in the oviducts. However, the structure of the oviduct cannot accommodate the growth of a fetus. Surgical removal of the ectopic pregnancy, resulting in an abortion, is thus required for the sake of the mother’s health. In the ongoing political and ethical debate about abortion, this circumstance is often noted as an acceptable exception, “to save the life of the mother.” 4. Programmed cell death in the formation of human hands is like carving. One begins with more “material” than is necessary and removes what is not needed to reveal the final shape. 5. All vertebrates develop in a fluid environment. Fish and amphibians typically lay their eggs in water. Amniotes (reptiles, birds, and mammals) are defined by the presence of an amniotic sac, a self-contained aquatic system that surrounds the embryo with water inside the egg. The evolution of the amniotic egg removed the need to reproduce near water, freeing amniotes to reproduce underground, in deserts, and in trees! 6. Morning sickness typically occurs during the first trimester and subsides during the second. However, a great deal of variation in the timing and degree of symptoms is known. Unfortunately, the precise cause of morning sickness remains unknown. 7. Most human babies weigh 3–4 kilograms (kg) at birth. Birth weights much larger or smaller than this are associated with increased mortality. This is an example of stabilizing selection, discussed in Chapter 13. 8. When discussing the dilation of the cervix as part of labor, it might be useful to note that cigarettes are 90–100 mm long. Thus, a fully dilated cervix is about as wide as a cigarette is long. 9. The descriptions of basic development address questions that students may have never thought to ask. How do we get so many cells (trillions!) in our adult bodies? How do basic tissues, organs, and organ systems form? What mechanisms permit the coordinated development of the body? Before beginning this chapter, consider challenging your students with some of these fundamental questions: How did you get a heart, a brain, and ears? What determined when you were ready to be born? How did you get nutrients and oxygen before you could eat or breathe? 10. The many benefits of breastfeeding are noted at the web site of the U.S. Dept. of Health and Human Services, which can be found at 79

Fertilization The shape of a human sperm is streamlined, which helps it swim through fluids in the vagina, uterus, and oviduct. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think that fetal blood and mother’s blood run together, one into the other. Few students typically have a good understanding of the relationship of fetal and maternal blood in the placenta. 2. The extraembryonic membranes surrounding a human embryo are also not well understood by college students outside of the health sciences. These extraembryonic membranes can be viewed as analogous to the life-support systems used by astronauts. Teaching Tips 1. Gastrulation establishes the basic body plan by positioning the future systems of the body in relationship to each other. This essential element of gastrulation is a crucial event that is a prerequisite for later developmental events (and thus is the basis of the quote directly below). 2. You might wish to reflect on the somewhat famous quote of Lewis Wolpert, who in 1986 said, “It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.” The development and arrangement of the basic embryonic layers (ectoderm: skin and nervous system; mesoderm: muscle and bone; and endoderm: digestive tract) establishes the basic body plan. 3. Ectopic pregnancies occur when an embryo implants anywhere other than the uterus. Most frequently, ectopic pregnancies occur in the oviducts. However, the structure of the oviduct cannot accommodate the growth of a fetus. Surgical removal of the ectopic pregnancy, resulting in an abortion, is thus required for the sake of the mother’s health. In the ongoing political and ethical debate about abortion, this circumstance is often noted as an acceptable exception, “to save the life of the mother.” 4. Programmed cell death in the formation of human hands is like carving. One begins with more “material” than is necessary and removes what is not needed to reveal the final shape. 5. All vertebrates develop in a fluid environment. Fish and amphibians typically lay their eggs in water. Amniotes (reptiles, birds, and mammals) are defined by the presence of an amniotic sac, a self-contained aquatic system that surrounds the embryo with water inside the egg. The evolution of the amniotic egg removed the need to reproduce near water, freeing amniotes to reproduce underground, in deserts, and in trees! 6. Morning sickness typically occurs during the first trimester and subsides during the second. However, a great deal of variation in the timing and degree of symptoms is known. Unfortunately, the precise cause of morning sickness remains unknown. 7. Most human babies weigh 3–4 kilograms (kg) at birth. Birth weights much larger or smaller than this are associated with increased mortality. This is an example of stabilizing selection, discussed in Chapter 13. 8. When discussing the dilation of the cervix as part of labor, it might be useful to note that cigarettes are 90–100 mm long. Thus, a fully dilated cervix is about as wide as a cigarette is long. 9. The descriptions of basic development address questions that students may have never thought to ask. How do we get so many cells (trillions!) in our adult bodies? How do basic tissues, organs, and organ systems form? What mechanisms permit the coordinated development of the body? Before beginning this chapter, consider challenging your students with some of these fundamental questions: How did you get a heart, a brain, and ears? What determined when you were ready to be born? How did you get nutrients and oxygen before you could eat or breathe? 10. The many benefits of breastfeeding are noted at the web site of the U.S. Dept. of Health and Human Services, which can be found at 80

(carries genetic material)
Figure 26.11 Head (carries genetic material) Plasma membrane Mitochondria (produce energy) Nucleus Acrosome Flagellum (used for swimming) Figure A human sperm cell

Figure 26.12c Colorized SEM Figure Fertilization (SEM)

Cleavage of embryo starts. 4 The embryo develops into a blastocyst. 5
Figure 3 Cleavage of embryo starts. 4 The embryo develops into a blastocyst. 5 The blastocyst implants in the endometrium. Oviduct 2 Sperm fertilizes ovum, forming a zygote. Ovary 1 Ovulation releases secondary oocyte. Endometrium Uterus Figure Early stages of human development (step 5)

Pregnancy and Early Development
About a month after conception, four life-supporting pieces of equipment have formed: the amnion, a fluid-filled sac that encloses and protects the embryo, the yolk sac, which produces the first blood cells and first gamete-producing cells in the gonads, © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think that fetal blood and mother’s blood run together, one into the other. Few students typically have a good understanding of the relationship of fetal and maternal blood in the placenta. 2. The extraembryonic membranes surrounding a human embryo are also not well understood by college students outside of the health sciences. These extraembryonic membranes can be viewed as analogous to the life-support systems used by astronauts. Teaching Tips 1. Gastrulation establishes the basic body plan by positioning the future systems of the body in relationship to each other. This essential element of gastrulation is a crucial event that is a prerequisite for later developmental events (and thus is the basis of the quote directly below). 2. You might wish to reflect on the somewhat famous quote of Lewis Wolpert, who in 1986 said, “It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.” The development and arrangement of the basic embryonic layers (ectoderm: skin and nervous system; mesoderm: muscle and bone; and endoderm: digestive tract) establishes the basic body plan. 3. Ectopic pregnancies occur when an embryo implants anywhere other than the uterus. Most frequently, ectopic pregnancies occur in the oviducts. However, the structure of the oviduct cannot accommodate the growth of a fetus. Surgical removal of the ectopic pregnancy, resulting in an abortion, is thus required for the sake of the mother’s health. In the ongoing political and ethical debate about abortion, this circumstance is often noted as an acceptable exception, “to save the life of the mother.” 4. Programmed cell death in the formation of human hands is like carving. One begins with more “material” than is necessary and removes what is not needed to reveal the final shape. 5. All vertebrates develop in a fluid environment. Fish and amphibians typically lay their eggs in water. Amniotes (reptiles, birds, and mammals) are defined by the presence of an amniotic sac, a self-contained aquatic system that surrounds the embryo with water inside the egg. The evolution of the amniotic egg removed the need to reproduce near water, freeing amniotes to reproduce underground, in deserts, and in trees! 6. Morning sickness typically occurs during the first trimester and subsides during the second. However, a great deal of variation in the timing and degree of symptoms is known. Unfortunately, the precise cause of morning sickness remains unknown. 7. Most human babies weigh 3–4 kilograms (kg) at birth. Birth weights much larger or smaller than this are associated with increased mortality. This is an example of stabilizing selection, discussed in Chapter 13. 8. When discussing the dilation of the cervix as part of labor, it might be useful to note that cigarettes are 90–100 mm long. Thus, a fully dilated cervix is about as wide as a cigarette is long. 9. The descriptions of basic development address questions that students may have never thought to ask. How do we get so many cells (trillions!) in our adult bodies? How do basic tissues, organs, and organ systems form? What mechanisms permit the coordinated development of the body? Before beginning this chapter, consider challenging your students with some of these fundamental questions: How did you get a heart, a brain, and ears? What determined when you were ready to be born? How did you get nutrients and oxygen before you could eat or breathe? 10. The many benefits of breastfeeding are noted at the web site of the U.S. Dept. of Health and Human Services, which can be found at 84

the allantois, which helps form the umbilical cord, and the chorion, which contributes to the placenta. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think that fetal blood and mother’s blood run together, one into the other. Few students typically have a good understanding of the relationship of fetal and maternal blood in the placenta. 2. The extraembryonic membranes surrounding a human embryo are also not well understood by college students outside of the health sciences. These extraembryonic membranes can be viewed as analogous to the life-support systems used by astronauts. Teaching Tips 1. Gastrulation establishes the basic body plan by positioning the future systems of the body in relationship to each other. This essential element of gastrulation is a crucial event that is a prerequisite for later developmental events (and thus is the basis of the quote directly below). 2. You might wish to reflect on the somewhat famous quote of Lewis Wolpert, who in 1986 said, “It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.” The development and arrangement of the basic embryonic layers (ectoderm: skin and nervous system; mesoderm: muscle and bone; and endoderm: digestive tract) establishes the basic body plan. 3. Ectopic pregnancies occur when an embryo implants anywhere other than the uterus. Most frequently, ectopic pregnancies occur in the oviducts. However, the structure of the oviduct cannot accommodate the growth of a fetus. Surgical removal of the ectopic pregnancy, resulting in an abortion, is thus required for the sake of the mother’s health. In the ongoing political and ethical debate about abortion, this circumstance is often noted as an acceptable exception, “to save the life of the mother.” 4. Programmed cell death in the formation of human hands is like carving. One begins with more “material” than is necessary and removes what is not needed to reveal the final shape. 5. All vertebrates develop in a fluid environment. Fish and amphibians typically lay their eggs in water. Amniotes (reptiles, birds, and mammals) are defined by the presence of an amniotic sac, a self-contained aquatic system that surrounds the embryo with water inside the egg. The evolution of the amniotic egg removed the need to reproduce near water, freeing amniotes to reproduce underground, in deserts, and in trees! 6. Morning sickness typically occurs during the first trimester and subsides during the second. However, a great deal of variation in the timing and degree of symptoms is known. Unfortunately, the precise cause of morning sickness remains unknown. 7. Most human babies weigh 3–4 kilograms (kg) at birth. Birth weights much larger or smaller than this are associated with increased mortality. This is an example of stabilizing selection, discussed in Chapter 13. 8. When discussing the dilation of the cervix as part of labor, it might be useful to note that cigarettes are 90–100 mm long. Thus, a fully dilated cervix is about as wide as a cigarette is long. 9. The descriptions of basic development address questions that students may have never thought to ask. How do we get so many cells (trillions!) in our adult bodies? How do basic tissues, organs, and organ systems form? What mechanisms permit the coordinated development of the body? Before beginning this chapter, consider challenging your students with some of these fundamental questions: How did you get a heart, a brain, and ears? What determined when you were ready to be born? How did you get nutrients and oxygen before you could eat or breathe? 10. The many benefits of breastfeeding are noted at the web site of the U.S. Dept. of Health and Human Services, which can be found at 85

The placenta develops fingerlike chorionic villi that absorb nutrients and oxygen from the mother’s blood and pass these substances to the embryo and allows protective antibodies to pass from the mother to the fetus. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think that fetal blood and mother’s blood run together, one into the other. Few students typically have a good understanding of the relationship of fetal and maternal blood in the placenta. 2. The extraembryonic membranes surrounding a human embryo are also not well understood by college students outside of the health sciences. These extraembryonic membranes can be viewed as analogous to the life-support systems used by astronauts. Teaching Tips 1. Gastrulation establishes the basic body plan by positioning the future systems of the body in relationship to each other. This essential element of gastrulation is a crucial event that is a prerequisite for later developmental events (and thus is the basis of the quote directly below). 2. You might wish to reflect on the somewhat famous quote of Lewis Wolpert, who in 1986 said, “It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.” The development and arrangement of the basic embryonic layers (ectoderm: skin and nervous system; mesoderm: muscle and bone; and endoderm: digestive tract) establishes the basic body plan. 3. Ectopic pregnancies occur when an embryo implants anywhere other than the uterus. Most frequently, ectopic pregnancies occur in the oviducts. However, the structure of the oviduct cannot accommodate the growth of a fetus. Surgical removal of the ectopic pregnancy, resulting in an abortion, is thus required for the sake of the mother’s health. In the ongoing political and ethical debate about abortion, this circumstance is often noted as an acceptable exception, “to save the life of the mother.” 4. Programmed cell death in the formation of human hands is like carving. One begins with more “material” than is necessary and removes what is not needed to reveal the final shape. 5. All vertebrates develop in a fluid environment. Fish and amphibians typically lay their eggs in water. Amniotes (reptiles, birds, and mammals) are defined by the presence of an amniotic sac, a self-contained aquatic system that surrounds the embryo with water inside the egg. The evolution of the amniotic egg removed the need to reproduce near water, freeing amniotes to reproduce underground, in deserts, and in trees! 6. Morning sickness typically occurs during the first trimester and subsides during the second. However, a great deal of variation in the timing and degree of symptoms is known. Unfortunately, the precise cause of morning sickness remains unknown. 7. Most human babies weigh 3–4 kilograms (kg) at birth. Birth weights much larger or smaller than this are associated with increased mortality. This is an example of stabilizing selection, discussed in Chapter 13. 8. When discussing the dilation of the cervix as part of labor, it might be useful to note that cigarettes are 90–100 mm long. Thus, a fully dilated cervix is about as wide as a cigarette is long. 9. The descriptions of basic development address questions that students may have never thought to ask. How do we get so many cells (trillions!) in our adult bodies? How do basic tissues, organs, and organ systems form? What mechanisms permit the coordinated development of the body? Before beginning this chapter, consider challenging your students with some of these fundamental questions: How did you get a heart, a brain, and ears? What determined when you were ready to be born? How did you get nutrients and oxygen before you could eat or breathe? 10. The many benefits of breastfeeding are noted at the web site of the U.S. Dept. of Health and Human Services, which can be found at 86

(c) Day 31: The embryo and its life-support equipment
Figure 26.16c Placenta Mother’s blood vessels Allantois (forms part of the umbilical cord) Amnion Yolk sac Embryo Chorion Chorionic villi (c) Day 31: The embryo and its life-support equipment Figure A human embryo: the first month: day 31 (part 3)

The Stages of Pregnancy
Pregnancy is divided into three trimesters of about 3 months each. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think that fetal blood and mother’s blood run together, one into the other. Few students typically have a good understanding of the relationship of fetal and maternal blood in the placenta. 2. The extraembryonic membranes surrounding a human embryo are also not well understood by college students outside of the health sciences. These extraembryonic membranes can be viewed as analogous to the life-support systems used by astronauts. Teaching Tips 1. Gastrulation establishes the basic body plan by positioning the future systems of the body in relationship to each other. This essential element of gastrulation is a crucial event that is a prerequisite for later developmental events (and thus is the basis of the quote directly below). 2. You might wish to reflect on the somewhat famous quote of Lewis Wolpert, who in 1986 said, “It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.” The development and arrangement of the basic embryonic layers (ectoderm: skin and nervous system; mesoderm: muscle and bone; and endoderm: digestive tract) establishes the basic body plan. 3. Ectopic pregnancies occur when an embryo implants anywhere other than the uterus. Most frequently, ectopic pregnancies occur in the oviducts. However, the structure of the oviduct cannot accommodate the growth of a fetus. Surgical removal of the ectopic pregnancy, resulting in an abortion, is thus required for the sake of the mother’s health. In the ongoing political and ethical debate about abortion, this circumstance is often noted as an acceptable exception, “to save the life of the mother.” 4. Programmed cell death in the formation of human hands is like carving. One begins with more “material” than is necessary and removes what is not needed to reveal the final shape. 5. All vertebrates develop in a fluid environment. Fish and amphibians typically lay their eggs in water. Amniotes (reptiles, birds, and mammals) are defined by the presence of an amniotic sac, a self-contained aquatic system that surrounds the embryo with water inside the egg. The evolution of the amniotic egg removed the need to reproduce near water, freeing amniotes to reproduce underground, in deserts, and in trees! 6. Morning sickness typically occurs during the first trimester and subsides during the second. However, a great deal of variation in the timing and degree of symptoms is known. Unfortunately, the precise cause of morning sickness remains unknown. 7. Most human babies weigh 3–4 kilograms (kg) at birth. Birth weights much larger or smaller than this are associated with increased mortality. This is an example of stabilizing selection, discussed in Chapter 13. 8. When discussing the dilation of the cervix as part of labor, it might be useful to note that cigarettes are 90–100 mm long. Thus, a fully dilated cervix is about as wide as a cigarette is long. 9. The descriptions of basic development address questions that students may have never thought to ask. How do we get so many cells (trillions!) in our adult bodies? How do basic tissues, organs, and organ systems form? What mechanisms permit the coordinated development of the body? Before beginning this chapter, consider challenging your students with some of these fundamental questions: How did you get a heart, a brain, and ears? What determined when you were ready to be born? How did you get nutrients and oxygen before you could eat or breathe? 10. The many benefits of breastfeeding are noted at the web site of the U.S. Dept. of Health and Human Services, which can be found at 88

5 weeks (35 days) 9 weeks (63 days) 14 weeks (98 days) Amnion
Figure 26.17a Amnion Placenta Umbilical cord 5 weeks (35 days) 9 weeks (63 days) 14 weeks (98 days) Figure The development of a human (part 1)

About 9 weeks after fertilization,
The First Trimester About 9 weeks after fertilization, the embryo is called a fetus, the embryo has all of its organs and major body parts, and the embryo’s limb buds have become tiny arms and legs with fingers and toes. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think that fetal blood and mother’s blood run together, one into the other. Few students typically have a good understanding of the relationship of fetal and maternal blood in the placenta. 2. The extraembryonic membranes surrounding a human embryo are also not well understood by college students outside of the health sciences. These extraembryonic membranes can be viewed as analogous to the life-support systems used by astronauts. Teaching Tips 1. Gastrulation establishes the basic body plan by positioning the future systems of the body in relationship to each other. This essential element of gastrulation is a crucial event that is a prerequisite for later developmental events (and thus is the basis of the quote directly below). 2. You might wish to reflect on the somewhat famous quote of Lewis Wolpert, who in 1986 said, “It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.” The development and arrangement of the basic embryonic layers (ectoderm: skin and nervous system; mesoderm: muscle and bone; and endoderm: digestive tract) establishes the basic body plan. 3. Ectopic pregnancies occur when an embryo implants anywhere other than the uterus. Most frequently, ectopic pregnancies occur in the oviducts. However, the structure of the oviduct cannot accommodate the growth of a fetus. Surgical removal of the ectopic pregnancy, resulting in an abortion, is thus required for the sake of the mother’s health. In the ongoing political and ethical debate about abortion, this circumstance is often noted as an acceptable exception, “to save the life of the mother.” 4. Programmed cell death in the formation of human hands is like carving. One begins with more “material” than is necessary and removes what is not needed to reveal the final shape. 5. All vertebrates develop in a fluid environment. Fish and amphibians typically lay their eggs in water. Amniotes (reptiles, birds, and mammals) are defined by the presence of an amniotic sac, a self-contained aquatic system that surrounds the embryo with water inside the egg. The evolution of the amniotic egg removed the need to reproduce near water, freeing amniotes to reproduce underground, in deserts, and in trees! 6. Morning sickness typically occurs during the first trimester and subsides during the second. However, a great deal of variation in the timing and degree of symptoms is known. Unfortunately, the precise cause of morning sickness remains unknown. 7. Most human babies weigh 3–4 kilograms (kg) at birth. Birth weights much larger or smaller than this are associated with increased mortality. This is an example of stabilizing selection, discussed in Chapter 13. 8. When discussing the dilation of the cervix as part of labor, it might be useful to note that cigarettes are 90–100 mm long. Thus, a fully dilated cervix is about as wide as a cigarette is long. 9. The descriptions of basic development address questions that students may have never thought to ask. How do we get so many cells (trillions!) in our adult bodies? How do basic tissues, organs, and organ systems form? What mechanisms permit the coordinated development of the body? Before beginning this chapter, consider challenging your students with some of these fundamental questions: How did you get a heart, a brain, and ears? What determined when you were ready to be born? How did you get nutrients and oxygen before you could eat or breathe? 10. The many benefits of breastfeeding are noted at the web site of the U.S. Dept. of Health and Human Services, which can be found at 90

Amnion Placenta Umbilical cord 9 weeks (63 days) Figure 26.17d
Figure The development of a human: 9 weeks (part 4)

The First Trimester By the end of the first trimester, the sex of the fetus can be determined by an ultrasound. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think that fetal blood and mother’s blood run together, one into the other. Few students typically have a good understanding of the relationship of fetal and maternal blood in the placenta. 2. The extraembryonic membranes surrounding a human embryo are also not well understood by college students outside of the health sciences. These extraembryonic membranes can be viewed as analogous to the life-support systems used by astronauts. Teaching Tips 1. Gastrulation establishes the basic body plan by positioning the future systems of the body in relationship to each other. This essential element of gastrulation is a crucial event that is a prerequisite for later developmental events (and thus is the basis of the quote directly below). 2. You might wish to reflect on the somewhat famous quote of Lewis Wolpert, who in 1986 said, “It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.” The development and arrangement of the basic embryonic layers (ectoderm: skin and nervous system; mesoderm: muscle and bone; and endoderm: digestive tract) establishes the basic body plan. 3. Ectopic pregnancies occur when an embryo implants anywhere other than the uterus. Most frequently, ectopic pregnancies occur in the oviducts. However, the structure of the oviduct cannot accommodate the growth of a fetus. Surgical removal of the ectopic pregnancy, resulting in an abortion, is thus required for the sake of the mother’s health. In the ongoing political and ethical debate about abortion, this circumstance is often noted as an acceptable exception, “to save the life of the mother.” 4. Programmed cell death in the formation of human hands is like carving. One begins with more “material” than is necessary and removes what is not needed to reveal the final shape. 5. All vertebrates develop in a fluid environment. Fish and amphibians typically lay their eggs in water. Amniotes (reptiles, birds, and mammals) are defined by the presence of an amniotic sac, a self-contained aquatic system that surrounds the embryo with water inside the egg. The evolution of the amniotic egg removed the need to reproduce near water, freeing amniotes to reproduce underground, in deserts, and in trees! 6. Morning sickness typically occurs during the first trimester and subsides during the second. However, a great deal of variation in the timing and degree of symptoms is known. Unfortunately, the precise cause of morning sickness remains unknown. 7. Most human babies weigh 3–4 kilograms (kg) at birth. Birth weights much larger or smaller than this are associated with increased mortality. This is an example of stabilizing selection, discussed in Chapter 13. 8. When discussing the dilation of the cervix as part of labor, it might be useful to note that cigarettes are 90–100 mm long. Thus, a fully dilated cervix is about as wide as a cigarette is long. 9. The descriptions of basic development address questions that students may have never thought to ask. How do we get so many cells (trillions!) in our adult bodies? How do basic tissues, organs, and organ systems form? What mechanisms permit the coordinated development of the body? Before beginning this chapter, consider challenging your students with some of these fundamental questions: How did you get a heart, a brain, and ears? What determined when you were ready to be born? How did you get nutrients and oxygen before you could eat or breathe? 10. The many benefits of breastfeeding are noted at the web site of the U.S. Dept. of Health and Human Services, which can be found at 92

Figure 26.18 Figure Ultrasound imaging

Figure 26.18a Figure Ultrasound imaging (part 1)

Figure 26.18b Figure Ultrasound imaging (part 2)

At about 14 weeks of development, the fetus
The Second Trimester At about 14 weeks of development, the fetus is about 6 cm (2.4 inches) long and starts to look distinctly human. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think that fetal blood and mother’s blood run together, one into the other. Few students typically have a good understanding of the relationship of fetal and maternal blood in the placenta. 2. The extraembryonic membranes surrounding a human embryo are also not well understood by college students outside of the health sciences. These extraembryonic membranes can be viewed as analogous to the life-support systems used by astronauts. Teaching Tips 1. Gastrulation establishes the basic body plan by positioning the future systems of the body in relationship to each other. This essential element of gastrulation is a crucial event that is a prerequisite for later developmental events (and thus is the basis of the quote directly below). 2. You might wish to reflect on the somewhat famous quote of Lewis Wolpert, who in 1986 said, “It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.” The development and arrangement of the basic embryonic layers (ectoderm: skin and nervous system; mesoderm: muscle and bone; and endoderm: digestive tract) establishes the basic body plan. 3. Ectopic pregnancies occur when an embryo implants anywhere other than the uterus. Most frequently, ectopic pregnancies occur in the oviducts. However, the structure of the oviduct cannot accommodate the growth of a fetus. Surgical removal of the ectopic pregnancy, resulting in an abortion, is thus required for the sake of the mother’s health. In the ongoing political and ethical debate about abortion, this circumstance is often noted as an acceptable exception, “to save the life of the mother.” 4. Programmed cell death in the formation of human hands is like carving. One begins with more “material” than is necessary and removes what is not needed to reveal the final shape. 5. All vertebrates develop in a fluid environment. Fish and amphibians typically lay their eggs in water. Amniotes (reptiles, birds, and mammals) are defined by the presence of an amniotic sac, a self-contained aquatic system that surrounds the embryo with water inside the egg. The evolution of the amniotic egg removed the need to reproduce near water, freeing amniotes to reproduce underground, in deserts, and in trees! 6. Morning sickness typically occurs during the first trimester and subsides during the second. However, a great deal of variation in the timing and degree of symptoms is known. Unfortunately, the precise cause of morning sickness remains unknown. 7. Most human babies weigh 3–4 kilograms (kg) at birth. Birth weights much larger or smaller than this are associated with increased mortality. This is an example of stabilizing selection, discussed in Chapter 13. 8. When discussing the dilation of the cervix as part of labor, it might be useful to note that cigarettes are 90–100 mm long. Thus, a fully dilated cervix is about as wide as a cigarette is long. 9. The descriptions of basic development address questions that students may have never thought to ask. How do we get so many cells (trillions!) in our adult bodies? How do basic tissues, organs, and organ systems form? What mechanisms permit the coordinated development of the body? Before beginning this chapter, consider challenging your students with some of these fundamental questions: How did you get a heart, a brain, and ears? What determined when you were ready to be born? How did you get nutrients and oxygen before you could eat or breathe? 10. The many benefits of breastfeeding are noted at the web site of the U.S. Dept. of Health and Human Services, which can be found at 96

Figure 26.17e 14 weeks (98 days) Figure The development of a human: 14 weeks (part 5)

The Second Trimester At 20 weeks, the fetus
is about 19 cm (7.6 inches) long, weighs about half a kilogram (1 lb), and has the face of an infant. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think that fetal blood and mother’s blood run together, one into the other. Few students typically have a good understanding of the relationship of fetal and maternal blood in the placenta. 2. The extraembryonic membranes surrounding a human embryo are also not well understood by college students outside of the health sciences. These extraembryonic membranes can be viewed as analogous to the life-support systems used by astronauts. Teaching Tips 1. Gastrulation establishes the basic body plan by positioning the future systems of the body in relationship to each other. This essential element of gastrulation is a crucial event that is a prerequisite for later developmental events (and thus is the basis of the quote directly below). 2. You might wish to reflect on the somewhat famous quote of Lewis Wolpert, who in 1986 said, “It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.” The development and arrangement of the basic embryonic layers (ectoderm: skin and nervous system; mesoderm: muscle and bone; and endoderm: digestive tract) establishes the basic body plan. 3. Ectopic pregnancies occur when an embryo implants anywhere other than the uterus. Most frequently, ectopic pregnancies occur in the oviducts. However, the structure of the oviduct cannot accommodate the growth of a fetus. Surgical removal of the ectopic pregnancy, resulting in an abortion, is thus required for the sake of the mother’s health. In the ongoing political and ethical debate about abortion, this circumstance is often noted as an acceptable exception, “to save the life of the mother.” 4. Programmed cell death in the formation of human hands is like carving. One begins with more “material” than is necessary and removes what is not needed to reveal the final shape. 5. All vertebrates develop in a fluid environment. Fish and amphibians typically lay their eggs in water. Amniotes (reptiles, birds, and mammals) are defined by the presence of an amniotic sac, a self-contained aquatic system that surrounds the embryo with water inside the egg. The evolution of the amniotic egg removed the need to reproduce near water, freeing amniotes to reproduce underground, in deserts, and in trees! 6. Morning sickness typically occurs during the first trimester and subsides during the second. However, a great deal of variation in the timing and degree of symptoms is known. Unfortunately, the precise cause of morning sickness remains unknown. 7. Most human babies weigh 3–4 kilograms (kg) at birth. Birth weights much larger or smaller than this are associated with increased mortality. This is an example of stabilizing selection, discussed in Chapter 13. 8. When discussing the dilation of the cervix as part of labor, it might be useful to note that cigarettes are 90–100 mm long. Thus, a fully dilated cervix is about as wide as a cigarette is long. 9. The descriptions of basic development address questions that students may have never thought to ask. How do we get so many cells (trillions!) in our adult bodies? How do basic tissues, organs, and organ systems form? What mechanisms permit the coordinated development of the body? Before beginning this chapter, consider challenging your students with some of these fundamental questions: How did you get a heart, a brain, and ears? What determined when you were ready to be born? How did you get nutrients and oxygen before you could eat or breathe? 10. The many benefits of breastfeeding are noted at the web site of the U.S. Dept. of Health and Human Services, which can be found at 98

Figure 26.17f 20 weeks (140 days) Figure The development of a human: 20 weeks (part 6)

The Third Trimester The third trimester At birth, a typical baby
is a time of rapid growth and includes many important physical changes. At birth, a typical baby is about 50 cm (20 inches) long and weighs 3–4 kg (6–8 lb). © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think that fetal blood and mother’s blood run together, one into the other. Few students typically have a good understanding of the relationship of fetal and maternal blood in the placenta. 2. The extraembryonic membranes surrounding a human embryo are also not well understood by college students outside of the health sciences. These extraembryonic membranes can be viewed as analogous to the life-support systems used by astronauts. Teaching Tips 1. Gastrulation establishes the basic body plan by positioning the future systems of the body in relationship to each other. This essential element of gastrulation is a crucial event that is a prerequisite for later developmental events (and thus is the basis of the quote directly below). 2. You might wish to reflect on the somewhat famous quote of Lewis Wolpert, who in 1986 said, “It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.” The development and arrangement of the basic embryonic layers (ectoderm: skin and nervous system; mesoderm: muscle and bone; and endoderm: digestive tract) establishes the basic body plan. 3. Ectopic pregnancies occur when an embryo implants anywhere other than the uterus. Most frequently, ectopic pregnancies occur in the oviducts. However, the structure of the oviduct cannot accommodate the growth of a fetus. Surgical removal of the ectopic pregnancy, resulting in an abortion, is thus required for the sake of the mother’s health. In the ongoing political and ethical debate about abortion, this circumstance is often noted as an acceptable exception, “to save the life of the mother.” 4. Programmed cell death in the formation of human hands is like carving. One begins with more “material” than is necessary and removes what is not needed to reveal the final shape. 5. All vertebrates develop in a fluid environment. Fish and amphibians typically lay their eggs in water. Amniotes (reptiles, birds, and mammals) are defined by the presence of an amniotic sac, a self-contained aquatic system that surrounds the embryo with water inside the egg. The evolution of the amniotic egg removed the need to reproduce near water, freeing amniotes to reproduce underground, in deserts, and in trees! 6. Morning sickness typically occurs during the first trimester and subsides during the second. However, a great deal of variation in the timing and degree of symptoms is known. Unfortunately, the precise cause of morning sickness remains unknown. 7. Most human babies weigh 3–4 kilograms (kg) at birth. Birth weights much larger or smaller than this are associated with increased mortality. This is an example of stabilizing selection, discussed in Chapter 13. 8. When discussing the dilation of the cervix as part of labor, it might be useful to note that cigarettes are 90–100 mm long. Thus, a fully dilated cervix is about as wide as a cigarette is long. 9. The descriptions of basic development address questions that students may have never thought to ask. How do we get so many cells (trillions!) in our adult bodies? How do basic tissues, organs, and organ systems form? What mechanisms permit the coordinated development of the body? Before beginning this chapter, consider challenging your students with some of these fundamental questions: How did you get a heart, a brain, and ears? What determined when you were ready to be born? How did you get nutrients and oxygen before you could eat or breathe? 10. The many benefits of breastfeeding are noted at the web site of the U.S. Dept. of Health and Human Services, which can be found at 100

At birth (280 days) Figure 26.17g
Figure The development of a human: at birth (part 7)

Childbirth The birth of a child is brought about by a series of strong, rhythmic contractions of the uterus called labor. Hormones such as oxytocin, a powerful stimulant of the smooth muscle walls in the uterus, play a key role in inducing labor. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think that fetal blood and mother’s blood run together, one into the other. Few students typically have a good understanding of the relationship of fetal and maternal blood in the placenta. 2. The extraembryonic membranes surrounding a human embryo are also not well understood by college students outside of the health sciences. These extraembryonic membranes can be viewed as analogous to the life-support systems used by astronauts. Teaching Tips 1. Gastrulation establishes the basic body plan by positioning the future systems of the body in relationship to each other. This essential element of gastrulation is a crucial event that is a prerequisite for later developmental events (and thus is the basis of the quote directly below). 2. You might wish to reflect on the somewhat famous quote of Lewis Wolpert, who in 1986 said, “It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.” The development and arrangement of the basic embryonic layers (ectoderm: skin and nervous system; mesoderm: muscle and bone; and endoderm: digestive tract) establishes the basic body plan. 3. Ectopic pregnancies occur when an embryo implants anywhere other than the uterus. Most frequently, ectopic pregnancies occur in the oviducts. However, the structure of the oviduct cannot accommodate the growth of a fetus. Surgical removal of the ectopic pregnancy, resulting in an abortion, is thus required for the sake of the mother’s health. In the ongoing political and ethical debate about abortion, this circumstance is often noted as an acceptable exception, “to save the life of the mother.” 4. Programmed cell death in the formation of human hands is like carving. One begins with more “material” than is necessary and removes what is not needed to reveal the final shape. 5. All vertebrates develop in a fluid environment. Fish and amphibians typically lay their eggs in water. Amniotes (reptiles, birds, and mammals) are defined by the presence of an amniotic sac, a self-contained aquatic system that surrounds the embryo with water inside the egg. The evolution of the amniotic egg removed the need to reproduce near water, freeing amniotes to reproduce underground, in deserts, and in trees! 6. Morning sickness typically occurs during the first trimester and subsides during the second. However, a great deal of variation in the timing and degree of symptoms is known. Unfortunately, the precise cause of morning sickness remains unknown. 7. Most human babies weigh 3–4 kilograms (kg) at birth. Birth weights much larger or smaller than this are associated with increased mortality. This is an example of stabilizing selection, discussed in Chapter 13. 8. When discussing the dilation of the cervix as part of labor, it might be useful to note that cigarettes are 90–100 mm long. Thus, a fully dilated cervix is about as wide as a cigarette is long. 9. The descriptions of basic development address questions that students may have never thought to ask. How do we get so many cells (trillions!) in our adult bodies? How do basic tissues, organs, and organ systems form? What mechanisms permit the coordinated development of the body? Before beginning this chapter, consider challenging your students with some of these fundamental questions: How did you get a heart, a brain, and ears? What determined when you were ready to be born? How did you get nutrients and oxygen before you could eat or breathe? 10. The many benefits of breastfeeding are noted at the web site of the U.S. Dept. of Health and Human Services, which can be found at 102

Childbirth Labor involves three stages:
dilation, the longest stage of labor, which increases the opening of the cervix, expulsion, which results in the delivery of the child, and delivery of the placenta usually within 15 minutes after the birth of the baby. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think that fetal blood and mother’s blood run together, one into the other. Few students typically have a good understanding of the relationship of fetal and maternal blood in the placenta. 2. The extraembryonic membranes surrounding a human embryo are also not well understood by college students outside of the health sciences. These extraembryonic membranes can be viewed as analogous to the life-support systems used by astronauts. Teaching Tips 1. Gastrulation establishes the basic body plan by positioning the future systems of the body in relationship to each other. This essential element of gastrulation is a crucial event that is a prerequisite for later developmental events (and thus is the basis of the quote directly below). 2. You might wish to reflect on the somewhat famous quote of Lewis Wolpert, who in 1986 said, “It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.” The development and arrangement of the basic embryonic layers (ectoderm: skin and nervous system; mesoderm: muscle and bone; and endoderm: digestive tract) establishes the basic body plan. 3. Ectopic pregnancies occur when an embryo implants anywhere other than the uterus. Most frequently, ectopic pregnancies occur in the oviducts. However, the structure of the oviduct cannot accommodate the growth of a fetus. Surgical removal of the ectopic pregnancy, resulting in an abortion, is thus required for the sake of the mother’s health. In the ongoing political and ethical debate about abortion, this circumstance is often noted as an acceptable exception, “to save the life of the mother.” 4. Programmed cell death in the formation of human hands is like carving. One begins with more “material” than is necessary and removes what is not needed to reveal the final shape. 5. All vertebrates develop in a fluid environment. Fish and amphibians typically lay their eggs in water. Amniotes (reptiles, birds, and mammals) are defined by the presence of an amniotic sac, a self-contained aquatic system that surrounds the embryo with water inside the egg. The evolution of the amniotic egg removed the need to reproduce near water, freeing amniotes to reproduce underground, in deserts, and in trees! 6. Morning sickness typically occurs during the first trimester and subsides during the second. However, a great deal of variation in the timing and degree of symptoms is known. Unfortunately, the precise cause of morning sickness remains unknown. 7. Most human babies weigh 3–4 kilograms (kg) at birth. Birth weights much larger or smaller than this are associated with increased mortality. This is an example of stabilizing selection, discussed in Chapter 13. 8. When discussing the dilation of the cervix as part of labor, it might be useful to note that cigarettes are 90–100 mm long. Thus, a fully dilated cervix is about as wide as a cigarette is long. 9. The descriptions of basic development address questions that students may have never thought to ask. How do we get so many cells (trillions!) in our adult bodies? How do basic tissues, organs, and organ systems form? What mechanisms permit the coordinated development of the body? Before beginning this chapter, consider challenging your students with some of these fundamental questions: How did you get a heart, a brain, and ears? What determined when you were ready to be born? How did you get nutrients and oxygen before you could eat or breathe? 10. The many benefits of breastfeeding are noted at the web site of the U.S. Dept. of Health and Human Services, which can be found at 103

Expulsion: delivery of the infant Delivery of the placenta
Figure 26.19 Placenta Umbilical cord Uterus Uterus Placenta (detaching) Cervix Umbilical cord 1 3 Dilation of the cervix 2 Expulsion: delivery of the infant Delivery of the placenta Figure The three stages of labor

Placenta Umbilical cord Uterus Cervix 1 Dilation of the cervix
Figure 26.19a Placenta Umbilical cord Uterus Cervix 1 Dilation of the cervix Figure The three stages of labor: dilation (part 1)

Expulsion: delivery of the infant
Figure 26.19b 2 Expulsion: delivery of the infant Figure The three stages of labor: expulsion (part 2)

Delivery of the placenta
Figure 26.19c Uterus Placenta (detaching) Umbilical cord 3 Delivery of the placenta Figure The three stages of labor: placenta delivery (part 3)

REPRODUCTIVE TECHNOLOGIES
Reproductive technologies can help solve problems related to the inability to conceive a child. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students frequently confuse the terms infertility and impotency. Care should be used to distinguish these terms. 2. Few students understand that many STDs can lead to infertility. For example, chlamydia is the most frequently reported bacterial sexually transmitted disease, according to the CDC. Infertility is a common consequence of chlamydia infections. Teaching Tips 1. Cardiovascular disease is often the cause of impotency (erectile dysfunction). Smoking, poor diet, and lack of exercise can therefore contribute to sexual problems. 2. The fate of surplus frozen embryos produced by in vitro fertilization is often debated. Some have suggested that they be used as sources of stem cells. Others regard this as a form of unacceptable abortion. Students might enjoy researching and discussing the issues related to these embryos. 108

Infertility Infertility is
the inability to have children after one year of trying, most often due to problems in the man, such as underproduction of sperm or poor sperm quality, and sometimes caused by impotence (erectile dysfunction), the inability to maintain an erection. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students frequently confuse the terms infertility and impotency. Care should be used to distinguish these terms. 2. Few students understand that many STDs can lead to infertility. For example, chlamydia is the most frequently reported bacterial sexually transmitted disease, according to the CDC. Infertility is a common consequence of chlamydia infections. Teaching Tips 1. Cardiovascular disease is often the cause of impotency (erectile dysfunction). Smoking, poor diet, and lack of exercise can therefore contribute to sexual problems. 2. The fate of surplus frozen embryos produced by in vitro fertilization is often debated. Some have suggested that they be used as sources of stem cells. Others regard this as a form of unacceptable abortion. Students might enjoy researching and discussing the issues related to these embryos. 109

Infertility Female infertility can result from
lack of eggs, failure to ovulate, or blocked oviducts. There are technologies available to help treat the many forms of infertility. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students frequently confuse the terms infertility and impotency. Care should be used to distinguish these terms. 2. Few students understand that many STDs can lead to infertility. For example, chlamydia is the most frequently reported bacterial sexually transmitted disease, according to the CDC. Infertility is a common consequence of chlamydia infections. Teaching Tips 1. Cardiovascular disease is often the cause of impotency (erectile dysfunction). Smoking, poor diet, and lack of exercise can therefore contribute to sexual problems. 2. The fate of surplus frozen embryos produced by in vitro fertilization is often debated. Some have suggested that they be used as sources of stem cells. Others regard this as a form of unacceptable abortion. Students might enjoy researching and discussing the issues related to these embryos. 110

In Vitro Fertilization
In vitro fertilization (IVF) begins with administration of drugs that promote the development of multiple eggs, followed by surgical removal of the eggs, collection of sperm, fertilization of the eggs with sperm in a petri dish, and injection of the resulting embryos into a uterus. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students frequently confuse the terms infertility and impotency. Care should be used to distinguish these terms. 2. Few students understand that many STDs can lead to infertility. For example, chlamydia is the most frequently reported bacterial sexually transmitted disease, according to the CDC. Infertility is a common consequence of chlamydia infections. Teaching Tips 1. Cardiovascular disease is often the cause of impotency (erectile dysfunction). Smoking, poor diet, and lack of exercise can therefore contribute to sexual problems. 2. The fate of surplus frozen embryos produced by in vitro fertilization is often debated. Some have suggested that they be used as sources of stem cells. Others regard this as a form of unacceptable abortion. Students might enjoy researching and discussing the issues related to these embryos. 111

In vitro fertilization Collected sperm
Figure 26.20 Implantation Early embryo Zygote Collected egg In vitro fertilization Collected sperm Figure In vitro fertilization

The Ethics of IVF IVF offers choices that nature does not and
raises many moral and legal issues. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students frequently confuse the terms infertility and impotency. Care should be used to distinguish these terms. 2. Few students understand that many STDs can lead to infertility. For example, chlamydia is the most frequently reported bacterial sexually transmitted disease, according to the CDC. Infertility is a common consequence of chlamydia infections. Teaching Tips 1. Cardiovascular disease is often the cause of impotency (erectile dysfunction). Smoking, poor diet, and lack of exercise can therefore contribute to sexual problems. 2. The fate of surplus frozen embryos produced by in vitro fertilization is often debated. Some have suggested that they be used as sources of stem cells. Others regard this as a form of unacceptable abortion. Students might enjoy researching and discussing the issues related to these embryos. 113

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