Q4. Why do not all copulations lead to fertilisation and pregnancy?
Fertilisation can occur only if the ovum and the sperms are transported to the ampullary region at the same time (NCERT page 35).
Q5. What happens in the secondary oocyte once a sperm enters it, and what does it give?
The sperm’s entry induces the completion of its second meiotic division, which is unequal: it gives a second polar body and a haploid ovum (ootid), whose nucleus then fuses with the sperm’s nucleus (NCERT page 36).
Q6. Assertion: a zygote with the chromosomes XY develops into a boy. Reason: the Y chromosome in it came from the mother’s ovum. Are both true, and does the reason explain the assertion?
The assertion is true but the reason is false: every ovum carries X; the Y comes from the father’s sperm (NCERT page 36).
Q7. Which part of the blastocyst becomes the embryo?
The inner cell mass (NCERT page 37).
Q8. Fill in the blanks: (c) Fertilisation is ____ in humans (external/internal). (e) Zygote is ____ (diploid/haploid). (h) The fusion of male and female gametes is called ____. (NCERT Exercise 1 c, e and h)
(c) Internal: the sperms are transferred into the female genital tract (insemination), and the ovum is fertilised in the ampullary region of the oviduct (NCERT pages 26 and 35). (e) Diploid: the haploid nuclei of the sperm and the ovum fuse to form a diploid zygote (NCERT page 36). (h) Fertilisation (NCERT pages 26 and 35).