NCERT Class 12 Biology: Chapter –3 Human Reproduction Part 6

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Question 9:

Give a schematic labelled diagram to represent oögenesis (without descriptions)

Answer:

Schematic labelled

Schematic Labelled

Schematic labelled

Question 10:

What are the changes in the Orgonial during the transition of a primary follicle to Graafian follicle?

Answer:

Changes that occur in the oogonia during the transition of a primary follicle to Graafian follicle are:

1. Germinal epithelial cells divide repeatedly to form multiple diploid oogonia.2. These oogonia grow to form primary oocyte.

3. These primary oocytes get surrounded by granulosa cells and form a primary follicle

4. Primary oocyte gets surrounded by more granulosa cells and forms a primary follicle.

5. Now this primary follicle, gets surrounded by more granular cells in order to form secondary follicle.

6. This secondary follicle converts into tertiary follicle by adding more granulosa cells.

7. The primary oocyte within the tertiary follicles, undergoes meiotic division in order to form secondary oocyte and a haploid polar body.

8. This tertiary follicle then, matures into Graafian follicle which in turn, ruptures to release secondary oocyte or ovum.

Long Answer Type Questions

Question 1:

What role does pituitary gonadotropins play during follicular and ovulatory phases of menstrual cycle? Explain the shifts in steroidal secretions.

Answer:

1. The two main pituitary gonadotropins are LH (luteinising hormone) and FSH (Follicle stimulating hormone). At the end of menstrual cycle, the amount of FSH increases that leads to the development of the follicles in the ovaries.

2. As follicles mature, oestrogen production increases. This in turn, increases the LH and FSH secretions.

3. The increased LH leads to ovulation and starts the formation of corpus luteum or luteinising.

4. Corpus luteum secretes progesterone and oestrogen which further maintains the endometrium lining.

Question 2:

Meiotic division during oogenesis is different from that in spermatogenesis. Explain how and why?

Answer:

1. Meiotic division during oogenesis is different from the one that occurs in spermatogenesis in terms of unequal division during oogenesis.

2. In spermatogenesis, all the four spermatids formed are equally functional in nature.

3. Whereas in oogenesis, unequal division takes place. In which major part of the cytoplasm remains in one ovum only.

4. Only a minor part of the ovum is separated as a polar body.

5. This division forms only one such ovum which is functional in nature.

This shows that, in spermatogenesis, all four spermatids formed are functional whereas in oogenesis only one ovum is functional.

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