1. 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

2. TOPIC 11 – ANIMAL PHYSIOLOGY
11.1
ANTIBODY PRODUCTION & VACCINATION
11.2
MOVEMENT
11.3
THE KIDNEY & OSMO-REGULATION
11.4
SEXUAL REPRODUCTION
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3. 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.
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4. 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.
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5. 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
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6. TESTIS STRUCTURE & FUNCTION
EPIDIDYMISA
TESTISB
SEMINIFEROUS TUBULEC
INTERSTITIUMD
VAS DEFERENSE E A D C B
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7. TESTIS STRUCTURE & FUNCTION
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8. 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
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9. 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.
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10. 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
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11. 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
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12. 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
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13. SPERMATOGENESIS
U.1
U.2
S.1
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14. SPERMATOGENESIS n n n 2n 2n n n n U.1 U.2 S.1 J WERBA – IB BIOLOGY 14
Ref:
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15. 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
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16. SPERMATOGENESIS
U.1
U.2
S.1
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17. 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.
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18. 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
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19. OVARY STRUCTURE & FUNCTION
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20. 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
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21. 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.
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22. OOGENESIS
U.1
U.2
When a baby girl is born, her ovaries contain at least 400,000 primary follicles.
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23. 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
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24. 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.
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25. OOGENESIS
U.1
U.2
When the mature follicle is released during ovulation, the egg is actually still a secondary oocyte.
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26. OOGENESIS
U.1
U.2
S.1
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27. 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.
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28. OOGENESIS
U.1
U.2
S.1
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29. OOGENESIS 2n 2n n n U.1 U.2 J WERBA – IB BIOLOGY 29
Ref:
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30. OOGENESIS
U.1
U.2
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31. 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
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32. OVUM STRUCTURE NUCLEUS CYTOPLASM (yolk) FIRST POLAR BODY
PLASMA MEMBRANE
CORONA RADIATA
ZONA PELLUCIDA
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33. 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.
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34. 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
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35. 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).
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36. 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!
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37. 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.
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38. 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
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39. 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 = ?????
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40. 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.
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41. 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.
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42. 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
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43. FERTILISATION
U.4
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44. FERTILISATION
U.4
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45. FERTILISATION
U.4
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46. 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.
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47. 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
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48. EARLY EMBRYONIC DEVELOPMENT
U.5
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49. 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.
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50. 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.
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51. 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.
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52. 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.
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53. THE PLACENTA
U.7
U.8
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54. 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.
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55. 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!
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56. BIRTH
U.9
It normally takes 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.
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57. 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.
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58. GESTATION PERIOD v BODY MASS
What is the correlation between adult body mass and gestation period in mammals?
humans
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59. 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.
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60. 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.
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61. 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.
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62. SEXUAL REPRODUCTION
Q1. Which of the cells labelled in the diagram below provides nourishment for developing sperm cells?
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63. SEXUAL REPRODUCTION
Q2. Which pair of statements best describes oogenesis and spermatogenesis?
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64. SEXUAL REPRODUCTION
Q3. Compare and contrast the processes of spermatogenesis and oogenesis. [8] Q4. Explain the function and structure of the placenta. [8]
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