Q4. A primary spermatocyte has 46 chromosomes. How many chromosomes are there in a secondary spermatocyte, a spermatid and a sperm?
23 in each: meiosis I halves the number, and meiosis II and spermiogenesis do not change it (NCERT page 31).
Q5. What is oogenesis? Give a brief account of it. (NCERT Exercise 12)
Oogenesis is the formation of a mature female gamete. Oogonia form in the fetal ovary and enter prophase I, where they arrest as primary oocytes, initially surrounded by flattened cells in primordial follicles (NCERT simplifies this as a primary follicle). Many follicles degenerate before puberty. Growing follicles become secondary and then tertiary follicles, in which the primary oocyte completes an unequal meiosis I, giving a secondary oocyte and a first polar body; the Graafian follicle releases the secondary oocyte at ovulation (NCERT pages 32–33). (Beyond the NCERT text: meiosis I is completed after the mid-cycle LH surge, in the follicle that is going to ovulate; Arroyo, Kim and Yeh, 2020.) The entry of a sperm induces the completion of the second meiotic division, also unequal, giving the ovum and a second polar body (NCERT page 36); until then the secondary oocyte waits in metaphase II (beyond the NCERT text; NCI SEER Training Modules, Ovaries).
Q6. Name the functions of (a) the acrosome and (b) the sperm tail. (NCERT Exercise 15 c and d)
(a) The acrosome is filled with enzymes that help fertilisation of the ovum. (b) The tail, powered by energy from the mitochondria of the middle piece, moves the sperm; motility supports natural fertilisation (NCERT page 32).
Q7. Assertion: the secondary oocyte is much larger than the first polar body. Reason: the first meiotic division of the primary oocyte is unequal. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion: the secondary oocyte keeps the bulk of the nutrient-rich cytoplasm (NCERT pages 32–33).
Q8. Fill in the blanks: (d) Male and female gametes are ____ (diploid/haploid). (f) The process of release of ovum from a mature follicle is called ____. (NCERT Exercise 1 d and f)
(d) Haploid, with 23 chromosomes (NCERT page 31). (f) Ovulation (NCERT page 33).
Q9. True or false: oogenesis takes place in the corpus luteum. Correct it if false. (NCERT Exercise 16 e)
False. Oogenesis takes place in the ovary, in its follicles (NCERT pages 32–33); the corpus luteum forms from the remains of the Graafian follicle after ovulation and secretes progesterone (NCERT page 35).