Q.What would be the number of chromosome in the spermatids?

Asexual reproduction produces clonal offspring from a single parent (e.g., fission, budding, fragmentation); alternatively, spermatogenesis is the meiotic, hormone-regulated formation of sperm from spermatogonia in the seminiferous tubules.

A note on scope: the 'Asexual Reproduction' half of this question belongs to the topic 'Reproduction in Organisms', a chapter that has been dropped from the current rationalised NCERT syllabus (it is retained here as basic biology background, since it is a standard OR alternative in this paper). The Gametogenesis/spermatogenesis half is fully within the current Human Reproduction chapter.

Option 1 — Asexual Reproduction:

Asexual reproduction is a mode of reproduction involving a single parent, in which offspring are produced without the fusion of gametes, and are genetically identical to the parent (clones).

Methods of asexual reproduction include: fission (binary and multiple), budding, fragmentation, spore formation, and vegetative propagation. Any three, described:

1. Fission: The parent organism divides into two (binary fission, e.g., Amoeba, Paramecium — divides into two equal daughter cells) or many (multiple fission, e.g., Plasmodium — the parent divides simultaneously into many daughter individuals under favourable conditions).
2. Budding: A small outgrowth called a bud develops on the parent body (e.g., Hydra), grows by repeated mitotic divisions, and eventually detaches to form a new independent individual; in yeast, small buds are produced that separate from the parent cell.
3. Fragmentation: The parent body breaks into two or more fragments (e.g., Spirogyra, a filamentous alga), and each fragment grows into a new, complete individual.

Option 2 — Gametogenesis & Spermatogenesis:

Gametogenesis is the biological process by which diploid (2n) germ cells undergo meiosis to form haploid (n) gametes (sperm in males, ova in females).

Spermatogenesis (its male form) occurs in the seminiferous tubules of the testis, beginning at puberty, and proceeds as follows:

1. Spermatogonia (2n), present along the inner wall of the seminiferous tubule, multiply by mitosis to increase in number.
2. Some spermatogonia periodically enlarge to become primary spermatocytes (2n).
3. Each primary spermatocyte undergoes the first meiotic division (meiosis I, reductional) to form two secondary spermatocytes (n, haploid).
4. The secondary spermatocytes undergo the second meiotic division (meiosis II, equational) to produce four haploid spermatids.
5. Spermatids are transformed into mature, motile spermatozoa through the process of spermiogenesis (development of the acrosome, condensation of the nucleus, formation of a flagellar tail, and loss of most cytoplasm).
6. Finally, sperm heads become embedded in the Sertoli cells and are later released into the lumen of the seminiferous tubule — a process called spermiation.

This entire process is regulated hormonally: the hypothalamus secretes GnRH, which stimulates the pituitary to release LH (acts on Leydig cells → testosterone secretion) and FSH (acts on Sertoli cells → stimulates spermiogenesis); testosterone in turn stimulates the process of spermatogenesis.

Gametogenesis forms haploid gametes by meiosis; spermatogenesis converts diploid spermatogonia into four haploid spermatozoa via mitotic multiplication, growth, meiotic maturation and spermiogenesis. The alternative answer describes the structure of the human male reproductive system.

Gametogenesis

Gametogenesis is the biological process by which the diploid germ cells of the gonads (testis in males, ovary in females) undergo meiosis to produce haploid gametes — spermatozoa in the male and ova in the female. Because it involves meiosis (a reductional division), the chromosome number is halved, so that fertilisation of two gametes restores the diploid number in the offspring.

Spermatogenesis — stages

Spermatogenesis occurs in the seminiferous tubules of the testis and passes through the following phases:

1. Multiplication phase: The undifferentiated germ cells, spermatogonia (2n), located at the periphery (basal membrane) of the seminiferous tubule, divide repeatedly by mitosis to increase in number.
2. Growth phase: Some spermatogonia periodically stop dividing and increase in size to become primary spermatocytes (2n).
3. Maturation phase: Each primary spermatocyte undergoes meiosis-I (reductional division) to form two haploid secondary spermatocytes (n). Each secondary spermatocyte then undergoes meiosis-II (equational division) to produce two spermatids — so one primary spermatocyte yields four haploid spermatids.
4. Spermiogenesis: The rounded, non-motile spermatids are transformed into elongated, motile spermatozoa — the acrosome (from the Golgi body) caps the nucleus, the nucleus condenses, mitochondria arrange in the middle piece, a flagellum (tail) develops, and most cytoplasm is shed.
5. Spermiation: The mature spermatozoa are finally released from the Sertoli cells into the lumen of the seminiferous tubule.

Diagrammatic representation (described): In a cross-section of a seminiferous tubule, cells are arranged from the outer basal membrane towards the central lumen in the order — spermatogonia (basal layer) → primary spermatocytes → secondary spermatocytes → spermatids → spermatozoa (nearest the lumen). Large, columnar Sertoli (nurse) cells span the full thickness of the tubule, nourishing the developing germ cells and secreting factors that support spermatogenesis; interstitial Leydig cells lie in the connective tissue between the tubules and secrete testosterone. (No image was supplied with this question, so the diagram is described in words above rather than drawn.)

OR — Human male reproductive system

The male reproductive system consists of:

• A pair of testes, located outside the abdominal cavity in a pouch called the scrotum, which maintains a temperature about 2–2.5°C lower than body temperature — necessary for normal spermatogenesis. Each testis has about 250 compartments called testicular lobules, each containing one to three highly coiled seminiferous tubules where sperm are produced. The tubules are lined by germ cells and Sertoli cells; the interstitial spaces between tubules contain small Leydig cells that synthesise testosterone.

• Accessory ducts: rete testis → vasa efferentia → epididymis (stores and matures sperm) → vas deferens (ascends and opens into the urethra along with the duct of the seminal vesicle as the ejaculatory duct) → urethra (common passage for both sperm and urine, opening through the penis).

• Accessory glands: a pair of seminal vesicles and the prostate gland, plus a pair of bulbourethral (Cowper's) glands, whose secretions constitute the seminal plasma — rich in fructose, calcium and enzymes — that nourishes and provides a medium for sperm transport, and lubricates the passage.

• External genitalia: the penis, a copulatory organ made of erectile tissue, whose enlarged end (glans penis) is covered by a fold of skin called the foreskin/prepuce.