Exercise 11.3
Assertion (A): The zygote formed after fertilisation immediately attaches to the uterus wall. Reason (R): The uterus wall is always prepared to receive the zygote. (i) Both A and R are true, and R is the correct explanation of A. (ii) Both A and R are true, but R is not the correct explanation of A. (iii) A is true, but R is false. (iv) A is false, but R is true.
Not cross-checked
NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.
NCERT’s answer
(iv)
(iv) A is false, but R is true.
A is false. The zygote does not attach immediately. It undergoes a series of mitotic divisions while it travels down the oviduct to the uterus, and only then implants into the inner lining — and it is that implantation, not fertilisation, that marks the beginning of pregnancy.
R is true in the sense meant: the uterus prepares itself in advance, not in response to a zygote. Before ovulation the inner lining becomes thick, and after ovulation it becomes thicker and richer in blood vessels — ready to receive and nourish a zygote should one arrive.
Once A is judged false, options (i), (ii) and (iii) are all eliminated, because each of them requires A to be true. Only (iv) remains.
