Human Reproduction, on the exam screen.

Secondary spermatocytes complete the second meiotic division to give haploid spermatids (III correct), and spermatids differentiate into spermatozoa by spermiogenesis (V correct). Statement I is wrong because spermatogonia divide mitotically, Statement II is wrong because primary spermatocytes undergo meiosis I, and Statement IV is wrong because spermatids transform (not divide by mitosis) into sperm. So only Statements III and V are correct, option (2).

Limbs and digits form by the end of the second month (about 8 weeks), so Q-III. Most major organ systems and the external genital organs are formed by the end of the first trimester (about 12 weeks), so R-IV. The first foetal movements and hair on the head appear around the fifth month (about 20 weeks), so P-II. By about 24 weeks the body is covered with fine hair with separated eyelids and eyelashes, so S-I. Hence P-II, Q-III, R-IV, S-I.

Moving inward from the outside of the secondary oocyte, the layers occur in the order corona radiata, then zona pellucida, then the perivitelline space, and finally the plasma membrane of the ovum. This corresponds to the sequence C, A, B, D. Hence option (3).

The sperm tail is a single long FLAGELLUM whose whip-like beating propels the cell forward. The energy comes from the mitochondria spiralled around the middle piece, which is why that region is packed with them. NCERT Class 12, Human Reproduction.

The infundibulum is the funnel-shaped opening of the FALLOPIAN TUBE, fringed with fimbriae that collect the ovum after ovulation - a female structure. The male duct system runs seminiferous tubules → rete testis → vasa efferentia → epididymis → vas deferens, and the other three options are all stages along it. NCERT Class 12, Human Reproduction.

A mid-cycle surge of luteinising hormone ruptures the mature Graafian follicle and releases the ovum. The remaining follicle forms the corpus luteum, whose main secretion is progesterone; it helps maintain the endometrium for implantation. Statement I is true, while statement II wrongly names oestrogen as the principal secretion.

The placenta functions as a temporary endocrine gland, producing human chorionic gonadotropin (hCG), human placental lactogen, oestrogens, progestogens and later relaxin. Luteinising hormone is not among them - LH is a gonadotropin secreted by the ANTERIOR PITUITARY. The placental hormone that mimics its role early in pregnancy is hCG, which sustains the corpus luteum. NCERT Class 12, Human Reproduction.

The zona pellucida is the transparent glycoprotein layer laid down around the oocyte during its growth, and it is the covering carried by the ovum at ovulation. It plays an active role at fertilisation, binding sperm and then hardening to block polyspermy once one sperm has entered. NCERT Class 12, Human Reproduction.

High concentrations of estrogen trigger the release of luteinizing hormone (LH), which in turn causes ovulation. Chapter: Human Reproduction.

Meiotic division of the secondary oocyte is completed at the time of fusion of a sperm with an ovum, forming the second polar body. Chapter: Human Reproduction.

The placenta secretes hCG; zona pellucida is the ovum's glycoprotein layer; bulbo-urethral secretions lubricate the penis; and Leydig cells secrete androgens. Thus P-II, Q-III, R-IV, S-I. Chapter: Human Reproduction.