1. B2.4 Sexual Reproduction in mammals
Red hunting
Describe the processes of oogenesis and spermatogenesis.
Describe the events of fertilisation from the first contact between the gametes to the fusion of nuclei.
Describe the early development of the embryo to blastocyst stage.

3. Spermatogenesis
Spermatogonia that enter either meiosis or mitosis first replicate their DNA. If mitosis occurs, two half size cells result If meiosis begins, four spermatozoa are the result. Each spermatozoon is very small and contains a haploid number of chromosomes. Watch the animation to illustrate this.

6. Testis tissue

15. Testes tissue 1 2 3 4

16. The cells involved
Sertoli cells – Provide nutrients for the developing spermatozoa while they develop their flagella. Leydig cells – Produce testosterone. Germinal epithelial cells – These are spermatogonia.

19. Hormonal control of sperm production
Hormonal changes are not as obviously cyclical as in females. Although some studies have shown that during a 24-hour period, there may be a surge of hormones.
Leutinizing hormone (LH) – Stimulates Leydig cells to produce testosterone.
Follicle stimulating hormone (FSH) and testosterone stimulate the meiotic division of spermatogonia into spermatozoa.

21. Male reproductive structures

22. Role of the epididymis, seminal vesicles and prostate
Sperm cells, once formed are stored in the epididymis – here they gain motility.
On sexual arousal, millions of sperm cells move from the epididymis into the vas deferens.
As they pass near the bladder, a high sugar (fructose) fluid is added from the seminal vesicle.
Prostate gland adds an alkaline substance
70% of fluid comes from seminal vesicles
30% from the prostate.

23. Oogenesis

24. Annotate a diagram of the ovary

25. Corpus Luteum – Secretes large amounts of oestrogen to inhibit further production of GnRH ad thus FSH and LH.

27. Before birth
In the ovaries cells called oogonia undergo mitosis to build up numbers.
They grow into larger primary oocytes.
Both oogonia and primary oocytes are diploid.
Primary oocytes start mitosis but stop during prophase I.
Also cells called follicles undergo mitosis.
A single layer of these cells surrounds each primary oocyte – we now refer to this entire structure as a primary follicle.

28. Events that occur during menstrual cycle
Each menstrual cycle a few primary follicles complete meiosis I.
This produce two cells, one large one small.
Small cell = first polar body
Large cell = Secondary oocyte.

29. And then… Single ring of follicle cells divide and form a fluid.
Two rings of follicle cells are formed with a fluid filled cavity separating them
First ring surrounds oocyte then fluid filled space and then the outer ring of follicle cells
Secondary oocyte begins meiosis II but stops during prophase.
We call this a Graafian follicle.

30. Oogenesis

32. 1. Compare the processes of spermatogenesis and oogenesis.
(Total 7 marks)

33. both involve meiosis; both involve cell proliferation / mitosis (before meiosis); both involve cell growth / enlargement (before meiosis); LH / FSH involved in both; testes versus ovaries; spermatogenesis starts at puberty versus oogenesis starts in the fetus; spermatogenesis until death versus oogenesis until menopause; spermatogenesis continuously versus oogenesis in a cycle; millions of sperm daily versus one egg per month; ejaculation of sperm any time versus ovulation in middle of menstrual cycle; four sperm per meiosis / spermatogonium versus one egg per meiosis / oogonium; spermatogenesis involves equal divisions versus oogenesis involves unequal cell / cytoplasm divisions; no polar bodies in spermatogenesis versus 2 or 3 polar bodies in oogenesis; spermatogenesis involves Sertoli / nurse cells versus oogenesis does not; meiosis II completed before fertilization in spermatogenesis versus after in oogenesis; testosterone needed for spermatogenesis versus not needed for oogenesis;

34. Describe and explain how, in mammals, events following the acrosome reaction prevent more than one sperm fertilising an egg.
(4)

36. (a)  A scientist observed a fertilised sea urchin egg during the first few days after fertilisation.
Explain how this fertilised egg became a hollow structure.
(3)
(b)  The scientist found that 128 cells were present after a few days.
Calculate the number of rounds of cleavage that had taken place.

37. 2.
cell division by mitosis to form more cells / spermatogonia; growth of cells / spermatogonia to form larger cells / primary spermatocytes; cells / primary spermatocytes divide by meiosis; two divisions of meiosis; haploid cells / spermatids formed; differentiation of haploid cells / spermatids into sperm; growth of tail / other feature of differentiation; FSH, testosterone and LH all needed for spermatogenesis; sperm stored / maturation in epididymis / gain motility; fluid added to sperm by seminal vesicle (during ejaculation); fluid from seminal vesicle contains nutrients / mucus; fluid added to sperm by prostate gland (during ejaculation) / fluid from prostate gland contains alkali / minerals;

38. 2. Production of semen involves a series of processes, which in total take many weeks to carry out. Outline the processes involved in semen production from the start of sperm formation (spermatogenesis) to ejaculation.
(Total 8 marks)

39. Quiz