11.4b Oogenesis

19/03/2013 § Leave a comment

Honestly, the better and more efficient explanation of oogenesis can be found on the study guide, as opposed to the explanation offered on the course companion. The course companion does provide vocabulary, such as

  • the medulla, which is the central ovary tissue
  • the cortex, which is the surrounding ovary tissue (around the medulla)
  • the germinal epithelium is the outer layer of the ovary (doesn’t a male’s seminiferous tubules also have this?)
  • the primary follicle is the cell that has started meiosis with the surrounding follicle cells
  • the secondary oocyte normally resides inside a mature follicle over the process of oogenesis

Similarly to spermatogenesis, there is a lot of mitosis and meiosis involved in the production of an ovum, but one of the biggest differences is how much is produced and when. The germinal epithelium cells divide by mitosis to form multiple diploid cells that will grow into the primary oocytes. Once large enough, meiosis beings, and all of this occurs while the baby girl is still in her mother’s womb. The image below shows the rest of the cycle.

Clearly there are some similarities between spermatogenesis and oogenesis, as well as differences. Some similarities are:

  • both start with proliferation of cells through mitosis
  • both require cell growth before meiosis
  • both involve two divisions of meiosis
  • (and the obvious one) both produce gametes

A few differences (out of many!) are:

  • spermatogenesis produces millions of sperm a day while oogenesis produces one ovum every 28 days
  • sperm production starts during puberty for boys while the beginning stages of oogenesis starts while the females are still fetuses
  • spermatogenesis lasts an entire lifetime but oogenesis stops at menopause

Essay Questions

  1. Draw a labelled diagram of the adult female reproductive system. 4 marks
  2. Draw a labeled diagram of an adult male reproductive system. 6 marks
  3. Explain the processes involved in oogenesis in humans. 9 marks
  4. Draw the structure of a mature human egg. 4 marks
  5. Explain the role of hormones in the regulation of the menstrual cycle in human females. 8 marks
  6. Outline the levels of each of the hormones that control the menstrual cycle immediately before ovulation. 3 marks
  7. Explain the roles of LH and FSH in the menstrual cycle, including the timing of their secretion during the cycle. 6 marks
  8. Outline the roles of progesterone and estrogen in the human menstrual cycle. 6 marks
  9. Draw a labeled diagram of the structure of an ovary as seen using a light microscope. 5 marks
  10. Draw the structure of the human female reproductive system immediately before ovulation. (Only the ovaries, oviducts and uterus need to be shown.) 6 marks
  11. Draw a labelled diagram of a mature sperm. 5 marks
  12. Outline the process of spermatogenesis in humans. 5 marks
  13. 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. 8 marks
  14. Compare the process of spermatogenesis and oogenesis. 7 marks
  15. Discuss how, in humans, a larger number of sperms are produced than eggs. 4 marks
  16. Describe the process of fertilization in humans. 8 marks
  17. Describe the development of the early human embryo. 5 marks
  18. Outline the regulation of pregnancy by two named hormones. 4 marks
  19. Outline the role of human chorionic gonadotropin (HCG) in early pregnancy 2 marks
  20. Outline the way in which a pregnancy can be detected at a very early stage. 4 marks
  21. Compare the roles of LH and HCG in female reproduction. 2 marks
  22. State the role of the amniotic sac and the amniotic fluid. 2 marks
  23. Explain the function and structure of the placenta. 8 marks
  24. Outline the process of in vitro fertilization (IVF). 6 marks
  25. Discuss the ethical issues surrounding IVF. 6 marks
  26. Outline the role of positive feedback in the process of birth in humans. 4 marks



Page 278, sizes of sperm

1. Draw a graph of tail length and cross-sectional area of protein fibers in the eight species of animal.

Let’s say I drew this graph. I would have plotted it appropriately, with the cross-sectional area of fibrous sheaths in the x-axis and the length of sperm in the y-axis. The pattern this graph would create would be linear, similar to what a graph would look like if y equalled x.

2. Outline the relationship between tail length and cross-sectional area of protein fibbers.

As the cross-sectional area of protein fibers decreases, so does the length of the sperm, or its tail (which takes up the most of the length of the sperm). The relationship is linear – when the cross-sectional area increases or decreases, the length of sperm follows suit. The only exception is the bull, who, though it has a larger cross-sectional area than a mouse, has sperm with shorter length than the mouse.

3. Explain reasons for the relationship.

The cross-sectional area of protein fibers holds the mitochondria of the sperm, which is what produces the sperm cell’s energy. If the length of the sperm is long, it needs more energy to be able to move as fast as it does. Likewise, the more mitochondria there is in the sperm cell, the more energy it can provide, so naturally, the sperm would be longer in order to use that energy.

4. Discuss whether there is a relationship between the size of an animal and the size of its sperm.

It seems like the smaller the animal is, the longer the sperm is, except when we look at the sea urchin. The bull and human (and sea urchin) are the only three animals whose sperm cells are two-digit numbers while small rats, hamsters and guinea pigs have sperm cells at lengths of 100 – 250+ µm. Again, the sea urchin is the only exception, because the sea urchin is definitely smaller than a bull and human. On the other hand, it IS still larger than the hamsters, rats, mice and guinea pigs and is the only organism in the chart that has no mitochondria.

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