Sexual Reproduction in Animals Chapter 17 Sexual Reproduction in Animals

Objectives Students should be able to: Identify on diagrams of the male reproductive system and give functions of testes, scrotum, sperm ducts, prostate gland, urethra and penis Identify on diagrams of the female reproductive system and give functions of ovaries, oviducts, uterus, cervix and vagina

Briefly describe the menstrual cycle with reference to the alternation of menstruation and ovulation, the natural variation in length, and the fertile and infertile phases of the cycle with reference to the effects of progesterone and estrogen only Describe fertilisation and early development of the zygote simply in terms of the formation of a ball of cells which becomes implanted in the wall of the uterus

State the functions of the amniotic sac and the amniotic fluid Describe the functions of the placenta and umbilical cord in relation to exchange of dissolved nutrients, gases and excretory products (structure details are NOT required) Discuss the spread of human immunodeficiency virus (HIV) and methods by which it may be controlled

17.1 Sexual Reproduction in Animals Involves fusion of gametes Gametes come from different parents This method is typical of vertebrates

Where are gametes formed? Gametes are produced by special organs called gonads Male gametes (sperms)  testes (testis) Female gametes (eggs/ova)  ovaries (ovary) Involves mating process for sperms and eggs to meet

Gametes & body cell Normal cells have a diploid number (2n) of chromosomes Gametes have haploid number (n) of chromosomes Because normal body cells are produced by mitosis Gametes are produced by meiosis

Why should gametes have a haploid number of chromosomes? Nucleus of human body cell has 46 chromosomes = 23 pairs 23 chromosomes from father, 23 from mother, that is why gametes have only 23 chromosomes. Add up = 46

Reproductive System in Man Male Reproductive System Functions of important parts Testes – produces sperms and male sex hormones Scrotum – held the testes outside the body as production of sperm requires a lower temperature Sperm ducts – a muscular tube which force sperms through the urethra during copulation

Prostate gland – secretes fluid and enzymes which nourish and activates the sperms so that they can swim actively. Mixture of fluid and sperms is called semen Urethra – passageway for both urine and semen out of the body. Urine and semen do not pass through the urethra at the same time Penis – an organ used to transfer sperms to the female reproductive organs

Female Reproductive System Functions of important parts Ovaries – organs where eggs/ova and female sex hormones are produced. Oviducts – provide a passageway for the eggs to travel to the uterus. The place where fertilisation takes place Uterus – fetus develops during pregnancy - protects and nourishes the developing embryo - muscles contract to push fetus out during birth

Cervix – a ring of muscles which close the lower end of the uterus Cervix – a ring of muscles which close the lower end of the uterus. It enlarges to allow passage of the fetus during birth Vagina – a place for the deposition of sperms by the penis. It also serves as a passageway for the baby during childbirth

Comparison btw male and female gamete Sperm Egg Size Smaller in size Much bigger in size Numbers Produced in large numbers each time and throughout the lifetime of the animal One egg is produced every month and there is a fixed number of eggs at birth Mobility Able to swim Cannot move by itself

Menstrual Cycle A cycle of events that takes place in the female reproductive organs. The average menstrual cycle is about 28 days. Menstrual cycle can range from 21 to 33 days. This is the natural variation in the length of the menstrual cycle. The monthly discharge of blood is called menstruation. This usually lasts for 5 days

The cycle Day 1 – 5 Menstruation occurs (uterine lining breaks down and flows out of the body Day 6 – 13 Oestrogen is secreted which causes the repair and growth of lining of the uterus The uterine lining becomes thick and spongy with blood vessels

Day 14 (Ovulation) Day 15 – 28 Fertile period Progesterone is secreted. Some oestrogen is also secreted Day 15 – 28 Progesterone maintains the uterine lining by causing it to thicken further and be supplied with more blood vessels, preparing it for the fertilised egg It inhibits ovulation

The Cycle ….. If no fertilization occurs, the egg breaks down. Progesterone is not produced and so the uterine lining breaks down. Hence, menstruation begins after Day 28 If there is fertilization, uterus lining will not shed. Instead, it remains and help to support the developing embryo

Fertile and infertile periods of the menstrual cycle Fertilisation is possible from day 11 to 16. This is the fertile period The rest of the days make up the infertile period of the menstrual cycle (above mentioned is just a guideline because mentrual cycle can be affected by factors such as stress and malnutrition)

Fertilisation The egg released form the ovary is usually surrounded by a few layers of follicle cells. follicle cells Figure 17.11 page 325

Fertilisation The egg released form the ovary is usually surrounded by a few layers of follicle cells. follicle cells egg nucleus enzymes released by sperm sperms Figure 17.11 page 325 To penetrate the egg, the acrosome of the sperm releases an enzyme to disperse the follicle cells and break down part of the egg membranes for the sperm to enter. 1

Fertilisation The egg released form the ovary is usually surrounded by a few layers of follicle cells. follicle cells egg nucleus follicle cells dispersed enzymes released by sperm only one sperm nucleus enters the egg sperms Figure 17.11 page 325 To penetrate the egg, the acrosome of the sperm releases an enzyme to disperse the follicle cells and break down part of the egg membranes for the sperm to enter. 1

Fertilisation The egg released form the ovary is usually surrounded by a few layers of follicle cells. follicle cells egg nucleus follicle cells dispersed enzymes released by sperm only one sperm nucleus enters the egg sperms Figure 17.11 page 325 To penetrate the egg, the acrosome of the sperm releases an enzyme to disperse the follicle cells and break down part of the egg membranes for the sperm to enter. Only one sperm nucleus enters the egg. The haploid sperm nucleus fuses with the haploid egg nucleus, and a fertilised egg or diploid zygote is formed. 1 2

Fertilisation The egg released form the ovary is usually surrounded by a few layers of follicle cells. follicle cells egg nucleus follicle cells dispersed diploid nucleus zygote enzymes released by sperm The haploid nucleus of the sperm fuses with the haploid nucleus of the egg to form a diploid zygote. only one sperm nucleus enters the egg sperms Figure 17.11 page 325 To penetrate the egg, the acrosome of the sperm releases an enzyme to disperse the follicle cells and break down part of the egg membranes for the sperm to enter. Only one sperm nucleus enters the egg. The haploid sperm nucleus fuses with the haploid egg nucleus, and a fertilised egg or diploid zygote is formed. 1 2

Fertilisation The egg released form the ovary is usually surrounded by a few layers of follicle cells. follicle cells egg nucleus follicle cells dispersed diploid nucleus zygote enzymes released by sperm The haploid nucleus of the sperm fuses with the haploid nucleus of the egg to form a diploid zygote. only one sperm nucleus enters the egg sperms Figure 17.11 page 325 To penetrate the egg, the acrosome of the sperm releases an enzyme to disperse the follicle cells and break down part of the egg membranes for the sperm to enter. Only one sperm nucleus enters the egg. The haploid sperm nucleus fuses with the haploid egg nucleus, and a fertilised egg or diploid zygote is formed. As soon as the sperm has entered the egg, the membrane of the egg changes so that no other sperms can enter. The remaining sperms, which do not fertilise the egg, eventually die. 1 2 3

Development of the embryo Fertilized egg passes along the oviduct to the uterus Meanwhile it begins to divide to form a hollow ball of cells called embryo The embryo reaches the uterus and implants itself to the uterine lining

Subsequently, membranes develop to enclose the embryo. The embryo is enclosed in the amniotic fluid which has the functions: Supports and cushions the embryo before birth Shock absorber Protects embryo against mechanical injury During birth, it lubricates and reduces friction n the vagina It buoys up the fetus and allows it to move freely during growth

Villi grow from the embryo into the uterine wall The villi and the uterine wall in which the villi are embedded make up the placenta Placenta is formed partly from embryonic tissue and partly from the uterine lining The umbilical cord attaches the embryo to the placenta

Functions of Placenta Allows dissolved food substances and oxygen to diffuse from the mother’s blood into that of the embryo Allows metabolic waste products to diffuse from the embryonic blood capillaries into the mother’s bloodstream Allows antibodies to diffuse from the mother’s blood into the embryonic blood capillaries Produces progesterone which maintains uterine lining in healthy state during pregnancy

Functions of umbilical cord Contains 2 umbilical arteries that transport deoxygenated blood and metabolic waste products such as urea from the fetus to the placenta Contains 1 umbilical vein that transports oxygenated blood and food substances such as glucose and amino acids from the placenta to the fetus **Exchange of substances is through diffusion

Sexually Transmitted Diseases May be spread through sexual intercourse May also be transmitted through direct skin contact or when blood from an infected person gets into the bloodstream of an uninfected person STDs are caused by bacteria or viruses Can result in physical damage or even death

Acquired Immune Deficiency Syndrome (AIDS) Caused by Human Immunodeficiency Virus (HIV) HIV destroy the body’s immune system. Hence, infections which are normally mild may prove to be fatal to a person with AIDS

Signs and symptoms Chronic or persistent fever Severe diarrhoea lasting for months Pneumonia Kaposi’s sarcoma (cancer of the blood vessels) Brain infection Widespread tuberculosis

Mode of transmission Sexual intercourse with an infected person Sharing needles with an infected person e.g. drug abuse, tattooing, acupuncture, ear-piercing Blood transfusion from infected person During pregnancy from infected mother to fetus

AIDs Is not spread through toilet seats, door knobs, coughs, swimming pools or mosquitoes

Prevention and control Keep to one sex partner or do not have sex Males to wear condom Avoid drug abuse Avoid sharing instruments that are likely to break the skin and be contaminated with blood Go to reliable operators for services such as tattooing, acupuncture

4.1 D MCQ 1 D 4 C 6 C 7 D 10 A 11 A 12 C 13 C 14 B 17 C

Paper 2 2 P: Sperm Organ: Testis Q: Pollen Organ: Anther

2(b) R is the tail and it enables the sperm to swim up the female reproductive system to fuse with the egg. S is the pollen tube. It grows into the style all the way to the ovary. It guides the male gamete to the ovule for fusion to take place.

2(c) Similarities: T is the nucleus and it contains chromosomes Differences: T contains only half the number of chromosomes