SEXUAL REPRODUCTION AHL Topic 11.4 IB Biology Miss Werba Sexual reproduction involves the development and fusion of haploid gametes. AHL Topic 11.4 IB Biology Miss Werba

TOPIC 11 – ANIMAL PHYSIOLOGY 11.1 ANTIBODY PRODUCTION & VACCINATION 11.2 MOVEMENT 11.3 THE KIDNEY & OSMO-REGULATION 11.4 SEXUAL REPRODUCTION J WERBA – IB BIOLOGY 2

THINGS TO COVER Statement Guidance U.1 U.2 U.3 U.4 U.5 U.6 U.7 U.8 U.9 Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation. U.2 Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm. U.3 Fertilization in animals can be internal or external. U.4 Fertilization involves mechanisms that prevent polyspermy. Fertilization involves the acrosome reaction, fusion of the plasma membrane of the egg and sperm and the cortical reaction. U.5 Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy. U.6 HCG stimulates the ovary to secrete progesterone during early pregnancy. U.7 The placenta facilitates the exchange of materials between the mother and foetus. U.8 Oestrogen and progesterone are secreted by the placenta once it has formed. U.9 Birth is mediated by positive feedback involving oestrogen and oxytocin. J WERBA – IB BIOLOGY 3

THINGS TO COVER Statement Guidance A.1 S.1 S.2 NOS 4.8 The average 38-week pregnancy in humans can be positioned on a graph showing the correlation between animal size and the development of the young at birth for other mammals. S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis. S.2 Annotation of diagrams of mature sperm and egg to indicate functions. NOS 4.8 Assessing risks and benefits associated with scientific research— the risks to human male fertility were not adequately assessed before steroids related to progesterone and oestrogen were released into the environment as a result of the use of the female contraceptive pill. J WERBA – IB BIOLOGY 4

TESTIS STRUCTURE & FUNCTION Produce sperm by a process called spermatogenesis Produce the hormone testosterone The testis consists of many seminiferous (SN) tubules. Interstitial (Leydig) cells and blood capillaries lie between the SN tubules J WERBA – IB BIOLOGY 5

TESTIS STRUCTURE & FUNCTION EPIDIDYMISA TESTISB SEMINIFEROUS TUBULEC INTERSTITIUMD VAS DEFERENSE E A D C B J WERBA – IB BIOLOGY 6

TESTIS STRUCTURE & FUNCTION J WERBA – IB BIOLOGY 7

TESTIS STRUCTURE & FUNCTION SEMINIFEROUS TUBULEC BASEMENT MEMBRANEG SERTOLI CELLSH GERMINAL EPITHELIUM CELLSI SPERMATOZOAJ LUMEN OF SN TUBULEK LEYDIG CELLSL C G H I J K L J WERBA – IB BIOLOGY 8

TESTIS STRUCTURE & FUNCTION Leydig (interstitial cells): produce testosterone germinal epithelium cells: origin of spermatogonia spermatozoa: developing sperm cells Sertoli cells: nourish developing spermatozoa Spermatozoa will eventually leave the SN tubule via the lumen. J WERBA – IB BIOLOGY 9

SPERMATOGENESIS U.1 11.4.2 1) Mitosis: germ cells (or spermatogonia (2n)) divide to produce more spermatogonia (2n). 2) Growth: spermatogonia grow larger becoming primary spermatocytes (2n) 3) Meiosis I: primary spermatocytes undergo Meiosis I producing two secondary spermatocytes (n) 10 J WERBA – IB BIOLOGY 10 10

SPERMATOGENESIS U.1 11.4.2 4) Meiosis II: secondary spermatocytes undergo Meiosis II producing two spermatids (n) per cell. 5) Development & cell differentiation: spermatids associate with Sertoli cells, developing into spermatozoa (n) 6) Detachment: sperm detach and are carried out of the testis by the fluid in the centre of the seminiferous tubule 11 J WERBA – IB BIOLOGY 11 11

SPERMATOGENESIS U.1 U.2 S.1 BASEMENT MEMBRANEJ SERTOLI CELLSO SPERMATO GONIUMK PRIMARY SPERMATO CYTEL SECONDAR Y SPERMATO CYTEM SPERMATID N SPERMATOZ OANP P P P P P O N N N O N N N N N N M M M M L M L L L K K K K K O O J 12 J WERBA – IB BIOLOGY 12 12

SPERMATOGENESIS U.1 U.2 S.1 J WERBA – IB BIOLOGY 13 13

SPERMATOGENESIS n n n 2n 2n n n n U.1 U.2 S.1 J WERBA – IB BIOLOGY 14 Ref: http://www.ib.bioninja.com.au/ J WERBA – IB BIOLOGY 14 14

SPERM STRUCTURE S.2 You need to be able to annotate a diagram to indicate functions. NUCLEUS ACROSOME MITOCHONDRIA HEAD MIDPIECE TAIL contains the haploid nucleus and acrosome, which carries enzymes necessary to penetrate the egg (by digesting the zona pellucida) contains many mitochondria to generate ATP for swimming propels the sperm as it swims towards the egg J WERBA – IB BIOLOGY 15

SPERMATOGENESIS U.1 U.2 S.1 J WERBA – IB BIOLOGY 16

OVARY STRUCTURE & FUNCTION The ovaries contain follicles in different stages of development. The follicles contain the developing oocytes. The germinal epithelium keeps the tissues of the organ together and separates them from the rest of the body. J WERBA – IB BIOLOGY 17

OVARY STRUCTURE & FUNCTION FALLOPIAN TUBEA OVARYB GERMINAL EPITHELIUMC PRIMARY OOCYTE D IN PRIMARY FOLLICLE D1 SECONDARY OOCYTE E IN GRAAFIAN FOLLICLEE1 OVULATIONF RUPTURED FOLLICLEG OVUMH CORPUS LUTEUMI A D D1 B C E1 E H F G J WERBA – IB BIOLOGY I 18 18

OVARY STRUCTURE & FUNCTION J WERBA – IB BIOLOGY 19

OVARY STRUCTURE & FUNCTION germinal epithelium cells: outer layer produces primary follicles through cell division primary follicles: Location for development of oocyte Surrounded by support cells mature follicle: contain oocyte, ready for ovulation secondary oocyte: haploid gamete Ovum held in state of suspended meiosis until after fertilisation J WERBA – IB BIOLOGY 20

OOGENESIS U.1 U.2 1) Mitosis: (in foetal ovaries) germ cells called oogonia (2n) form more oogonia (2n) 2) Growth: oogonia grow larger becoming primary oocytes (2n) 3) Meiosis I: primary oocytes begin Meiosis I but stop in Prophase I. The primary oocyte and a single layer of follicle cells form the primary follicle. J WERBA – IB BIOLOGY 21

OOGENESIS U.1 U.2 When a baby girl is born, her ovaries contain at least 400,000 primary follicles. J WERBA – IB BIOLOGY 22

OOGENESIS U.1 U.2 4) Meiosis I continues: every menstrual cycle, a few primary follicles start to develop. The primary oocyte completes Meiosis I, forming two haploid nuclei. 5) Unequal division: the cytoplasm of the primary oocyte divides unequally forming a large secondary oocyte (n) and a small polar body J WERBA – IB BIOLOGY 23

OOGENESIS U.1 U.2 6) Meiosis II: The secondary oocyte begins Meiosis II but stops in Prophase II. The follicle cells meanwhile are proliferating and follicular fluid is forming. J WERBA – IB BIOLOGY 24

OOGENESIS U.1 U.2 When the mature follicle is released during ovulation, the egg is actually still a secondary oocyte. J WERBA – IB BIOLOGY 25

OOGENESIS U.1 U.2 S.1 J WERBA – IB BIOLOGY 26

OOGENESIS U.1 U.2 7) Meiosis II continues: After fertilisation, the secondary oocyte completes Meiosis II to form an ovum. The ovum already has a sperm nucleus inside it and a second polar body. The first and second bodies do not develop and eventually degenerate. J WERBA – IB BIOLOGY 27

OOGENESIS U.1 U.2 S.1 J WERBA – IB BIOLOGY 28

OOGENESIS 2n 2n n n U.1 U.2 J WERBA – IB BIOLOGY 29 Ref: http://www.ib.bioninja.com.au/ J WERBA – IB BIOLOGY 29

OOGENESIS U.1 U.2 J WERBA – IB BIOLOGY 30

OVUM STRUCTURE S.2 You need to be able to annotate a diagram to indicate functions. CORONA RADIATA layer of follicle cells which nourish egg NUCLEUS ZONA PELLUCIDA layer of gel (glycoproteins) CYTOPLASM (yolk) contains nucleus, fat droplets, cortical granules, etc PLASMA MEMBRANE FIRST POLAR BODY J WERBA – IB BIOLOGY 31

OVUM STRUCTURE NUCLEUS CYTOPLASM (yolk) FIRST POLAR BODY PLASMA MEMBRANE CORONA RADIATA ZONA PELLUCIDA J WERBA – IB BIOLOGY 32

FERTILISATION U.3 The joining of sperm and egg cells is called fertilisation. This process combines the genetic material from the nucleus (n) of each parent together and results in the formation of a zygote (2n). Fertilisation can be internal or external. J WERBA – IB BIOLOGY 33

FERTILISATION External fertilisation: U.3 External fertilisation: In some animals, especially aquatic species (those that live or breed in water), fertilisation occurs outside the female’s body. Both the male and female will release their gametes into the water. Makes fertilisation susceptible to environmental variation. Often produce a large number of eggs/sperm to compensate for losses. eg. fish, amphibians J WERBA – IB BIOLOGY 34

FERTILISATION Internal fertilisation: U.3 Internal fertilisation: Occurs in animals that live and breed on land. This keeps the gametes inside the body so there is no chance of dehydration occurring. Sperm are introduced into the female by a process called copulation (or sexual intercourse). J WERBA – IB BIOLOGY 35

FERTILISATION U.4 The sperm are deposited into the vagina and travel through the uterus to the fallopian tubes. Fertilisation can occur here, and the fertilised ovum then makes its way to the endometrium to implant. But – there is more to fertilisation than the fusion of gametes! J WERBA – IB BIOLOGY 36

FERTILISATION U.4 There are a number of steps that occur during fertilisation of a sperm and egg: ACROSOME REACTION PENETRATION OF EGG BY THE SPERM CORTICAL REACTION These mechanisms prevent polyspermy, or fertilisation of the egg by more than one sperm. J WERBA – IB BIOLOGY 37

FERTILISATION Reminder: U.4 Reminder: At the moment of ovulation, the secondary oocyte is surrounded by the zona pellucida and a corona radiata: Corona radiata: The layer of follicle cells surrounding the zona pellucida Zona Pellucida: the membrane surrounding the secondary oocyte of mammals, which is secreted by the ovarian follicle cells J WERBA – IB BIOLOGY 38

FERTILISATION ACROSOME REACTION: Proteolytic = ????? U.4 ACROSOME REACTION: Sperm reaches the corona radiata and moves through the cells The acrosome fuses with the zona pellucida Acrosome releases proteolytic enzymes and digests the gel Proteolytic = ????? J WERBA – IB BIOLOGY 39

FERTILISATION PENETRATION OF EGG BY THE SPERM: U.4 PENETRATION OF EGG BY THE SPERM: The sperm then reaches the egg membrane The egg membrane has special receptors to bind the sperm cell The head of the sperm fuses with the membrane of the secondary oocyte. J WERBA – IB BIOLOGY 40

FERTILISATION CORTICAL REACTION: U.4 CORTICAL REACTION: The cortical granules (lysosomes) release enzymes The zona pellucida thickens and the sperm-binding proteins are destroyed. This forms the “fertilisation envelope” (ie. a crust) Once formed, the envelope cannot be penetrated by other sperm cells. Now, the nucleus of the secondary oocyte completes meiosis II and then the egg and sperm nuclei fuse to form a diploid zygote. J WERBA – IB BIOLOGY 41

FERTILISATION ENVELOPE FORMED U.4 acrosome of sperm reaches zona pellucida ACROSOME REACTION enzymes released from acrosome digest the zona pellucida the membranes of the sperm and egg fuse CORTICAL REACTION enzymes from cortical granules fuse with egg plasma membrane. This thickens zona pellucida and destroys sperm-binding proteins. FERTILISATION ENVELOPE FORMED no more sperm can penetrate egg J WERBA – IB BIOLOGY 42

FERTILISATION U.4 J WERBA – IB BIOLOGY 43

FERTILISATION U.4 J WERBA – IB BIOLOGY 44

FERTILISATION U.4 J WERBA – IB BIOLOGY 45

EARLY EMBRYONIC DEVELOPMENT U.5 After fertilisation, the zygote undergoes several mitotic divisions. These are cleavage divisions as they are not followed by cell growth. Several cleavage divisions occur, which leads to the formation of the morula, a solid ball of cells. The morula reaches the uterus about four days after fertilisation. J WERBA – IB BIOLOGY 46

EARLY EMBRYONIC DEVELOPMENT U.5 After this, unequal divisions cause a fluid-filled cavity to form in the middle. This makes a blastocyst (at around 5 days). The blastocyst consists of: an inner mass of cells  the embryo an outer layer called the trophoblast  the placenta a fluid-filled cavity J WERBA – IB BIOLOGY 47

EARLY EMBRYONIC DEVELOPMENT U.5 J WERBA – IB BIOLOGY 48

HUMAN CHORIONIC GONADOTROPHIN (HCG) If fertilisation has occurred, it will take ~8 days for the blastocyst to embed itself into the endometrium. After implantation, the trophoblast of the embryo starts to secrete the hormone HCG (= human chorionic gonadotrophin). HCG stimulates the ovary to secrete progesterone during early pregnancy. J WERBA – IB BIOLOGY 49

HUMAN CHORIONIC GONADOTROPHIN (HCG) HCG concentration continues to rise for 8-10 weeks. HCG stimulates the corpus luteum to grow and continue secreting oestrogen and progesterone. Progesterone and oestrogen inhibit FSH and LH – so no more eggs are released. Progesterone maintains the endometrium. J WERBA – IB BIOLOGY 50

THE PLACENTA U.7 U.8 The placenta is a disc-shaped structure that nourishes the developing embryo. It is formed from the developing trophoblast upon implantation. The trophoblast invades the uterine wall. The umbilical cord connects the foetus to the placenta. J WERBA – IB BIOLOGY 51

THE PLACENTA U.7 U.8 The placenta has a rich blood supply: facilitating the exchange of materials between the maternal blood and foetal capillaries. The placenta has few, thin membranes: providing a short diffusion distance for materials. The placenta has villi: increases surface area for exchange. The placenta has a large TSA and many Rough ERs and vesicles: able to make and secrete HCG, oestrogen and progesterone. The placenta secretes anti-immune substances: avoids attack by immune system. J WERBA – IB BIOLOGY 52

THE PLACENTA U.7 U.8 J WERBA – IB BIOLOGY 53

THE PLACENTA U.7 U.8 The placenta takes over the hormonal role of the ovary (at ~12 weeks) It releases progesterone and oestrogen: Oestrogen stimulates growth of the muscles of the uterus (myometrium) and the development of the mammary glands. Progesterone maintains the endometrium, as well as reduces uterine contractions and maternal immune response (no antibodies against foetus). Both oestrogen and progesterone levels drop near time of birth. J WERBA – IB BIOLOGY 54

THE PLACENTA U.8 Materials are exchanged between the maternal and foetal blood in the placenta. The placenta is foetal tissue which invades maternal uterine tissue. An exchange of materials takes place by diffusion: the foetal blood becomes enriched with nutrients and oxygen the maternal blood takes up the waste products from the foetus, which will then be excreted. NB. materials are exchanged but the blood doesn’t mix! J WERBA – IB BIOLOGY 55

BIRTH U.9 It normally takes 38-40 weeks after conception for the foetus to be ready to be born. Progesterone levels will drop so that the uterus can have coordinated muscle contractions. The foetal head engages in the cervix. Stretch receptors in the uterus and cervix report the pressure to the brain and the pituitary gland releases oxytocin. Oxytocin initiates contractions in the myometrium. The contractions become longer & stronger. This creates a positive feedback loop and results in increasing the strength and duration of the contractions. J WERBA – IB BIOLOGY 56

BIRTH The cervix will dilate throughout this process. When the cervix is fully dilated, labour is over and the second stage (expulsion) begins. The child is born through the vagina. This stage usually takes no more than one hour. When the uterus is no longer pushing against something, the positive feedback loop is broken and contractions soon reduce. However, a few contractions are needed to expel the placenta from the uterine wall. This is the last stage of birth. J WERBA – IB BIOLOGY 57

GESTATION PERIOD v BODY MASS What is the correlation between adult body mass and gestation period in mammals? humans J WERBA – IB BIOLOGY 58

GESTATION PERIOD v BODY MASS The graph shows a strong positive correlation between adult body mass and gestation period in mammals. However, there are outliers: eg. animals with the same gestation period but highly varied body masses eg. animals with the same body mass but highly varied gestation periods The general rule is that animals with longer gestation periods give birth to offspring who are more developed at the time of birth. J WERBA – IB BIOLOGY 59

ORAL CONTRACEPTIVE PILL NOS 4.8 Assessing risks and benefits associated with scientific research The risks to human male fertility were not adequately assessed before steroids related to progesterone and oestrogen were released into the environment as a result of the use of the female contraceptive pill. J WERBA – IB BIOLOGY 60

ORAL CONTRACEPTIVE PILL NOS 4.8 Apparent decline in human male fertility has concerned some scientists. Has been attributed in part to the excretion of residues from oral contraceptives into drinking water supplies! Synthetic oestrogen (from oral contraceptives and veterinary and industrial sources) has been shown to affect ‘maleness’ of fish in rivers/streams. Some hypothesise that this could also be occurring in humans, but further studies are still on going. Benefits of using the pill need to be weighed against the suspected risks. J WERBA – IB BIOLOGY 61

SEXUAL REPRODUCTION Q1. Which of the cells labelled in the diagram below provides nourishment for developing sperm cells? J WERBA – IB BIOLOGY 62

SEXUAL REPRODUCTION Q2. Which pair of statements best describes oogenesis and spermatogenesis? J WERBA – IB BIOLOGY 63

SEXUAL REPRODUCTION Q3. Compare and contrast the processes of spermatogenesis and oogenesis. [8] Q4. Explain the function and structure of the placenta. [8] J WERBA – IB BIOLOGY 64