# Human Reproduction — Part A (NEET Biology Class 12): Reproductive Systems & Gametogenesis

Source: https://tracknation.in/story/human-reproduction-part-a-neet-biology-class-12-reproductive-systems-gametogenesis (TrackNation — free UPSC notes with PYQs)

> NEET Class 12 Human Reproduction, Part A, mined from NCERT: the male reproductive system (testis, seminiferous tubule, Sertoli vs Leydig cells, accessory ducts/glands), the female reproductive system (ovary, oviduct, uterus, mammary glands), spermatogenesis (hormonal control by GnRH/LH/FSH, sperm structure and counts) and oogenesis (follicle development, the unequal meiotic division, polar bodies). With 12 MCQs, 6 NEET PYQs and an Active Recall prompt.

## The Male Reproductive System

🎯 **NEET priority: High-yield.** *Part A of Human Reproduction — the reproductive systems and gametogenesis. Gametogenesis diagrams (spermatogenesis vs oogenesis) are a NEET perennial — expect a question almost every year.*

Humans are **sexually reproducing and viviparous**. The full reproductive sequence:
**gametogenesis** (sperm/ovum formation) → **insemination** (sperm
transfer) → **fertilisation** (gamete fusion → zygote) → **implantation**
→ **gestation** → **parturition**. Notably, sperm formation
**continues into old age** in men, but ovum formation **ceases around age
50** in women.

### The male reproductive system

- The **testes** sit in the **scrotum**, outside the abdomen, at
a temperature **2–2.5°C lower** than body temperature — essential for
**spermatogenesis**. Each testis (4–5 cm × 2–3 cm) has about
**250 testicular lobules**, each with 1–3 highly coiled
**seminiferous tubules** — the site of sperm production.

- The seminiferous tubule wall has two cell types: **spermatogonia** (germ
cells, undergo meiosis to form sperm) and **Sertoli cells** (provide nutrition to germ
cells — do NOT make sperm themselves). Outside the tubules, **Leydig (interstitial)
cells** synthesise **androgens** (testicular hormones).

- Sperm path: seminiferous tubule → **rete testis** → **vasa
efferentia** → **epididymis** → **vas deferens** → ejaculatory duct
→ **urethra**. Accessory glands — paired **seminal vesicles**, a single
**prostate**, paired **bulbourethral glands** — secrete the fructose- and
calcium-rich **seminal plasma**.

## The Female Reproductive System & Spermatogenesis

### The female reproductive system

- **Ovaries** (2–4 cm) produce the ovum and steroid hormones. Female
accessory ducts: paired **fallopian tubes/oviducts** (10–12 cm — infundibulum with
**fimbriae** → ampulla, the site of fertilisation → isthmus), a single
**uterus**, and the **vagina**.

- The uterine wall has **3 layers**: outer **perimetrium**,
middle muscular **myometrium** (contracts strongly at delivery), inner glandular
**endometrium** (undergoes cyclical change during menstruation). Mammary glands have
**15–20 mammary lobes** of milk-secreting **alveoli**.

- **Trap:** presence or absence of the **hymen is NOT a reliable
indicator** of virginity or sexual experience — it can tear from sport, a fall, or a tampon,
and sometimes persists after coitus.

### Spermatogenesis

- A **spermatogonium** is diploid (**46 chromosomes**) and
multiplies by mitosis. A **primary spermatocyte** undergoes meiosis I → two haploid
**secondary spermatocytes** (**23 chromosomes** each) → meiosis II → four
haploid **spermatids**. Spermatids transform into sperm by **spermiogenesis**;
release from the tubule is **spermiation**.

- Hormonal control: **GnRH** (hypothalamus) → **LH + FSH**
(anterior pituitary). **LH** acts on **Leydig cells** → androgen
secretion → drives spermatogenesis. **FSH** acts on **Sertoli cells** →
factors that aid spermiogenesis.

- Sperm structure: **head** (haploid nucleus + **acrosome** cap
of enzymes for fertilisation), **neck**, **middle piece** (packed with
**mitochondria** — energy for tail movement), **tail**. One ejaculation
releases **200–300 million sperms**; normal fertility needs
**≥60% normal shape/size** and **≥40% vigorous motility**.

## Oogenesis & Why This Matters for NEET

### Oogenesis

- Oogenesis starts in the **fetal ovary** — millions of
**oogonia** form, and **no new oogonia form after birth**. They enter
meiosis I and arrest as **primary oocytes**, each surrounded by granulosa cells to form
a **primary follicle**. Most degenerate; only **60,000–80,000 primary
follicles** remain per ovary at puberty.

- A primary follicle → **secondary follicle** → **tertiary follicle**
(develops a fluid-filled **antrum**) → **Graafian (mature) follicle**. The
primary oocyte completes meiosis I **inside the tertiary follicle**, an
**unequal division** giving a large haploid **secondary oocyte** + a tiny
**first polar body**. The secondary oocyte develops the **zona pellucida**
and is released at **ovulation** when the Graafian follicle ruptures.

### Spermatogenesis vs oogenesis — side by side

| **Feature**

 | **Spermatogenesis**

 | **Oogenesis**

 |
| Starts

 | At puberty

 | During fetal (embryonic) development

 |
| Continues

 | Lifelong, even in old age

 | Stops around age 50 (menopause)

 |
| Division of cytoplasm

 | Equal — 4 equal spermatids per primary spermatocyte

 | Unequal — 1 large secondary oocyte + tiny polar bodies

 |
| Product count per parent cell

 | 4 functional sperm

 | 1 functional ovum (+ polar bodies, which degenerate)

 |
| Meiosis I completed

 | Continuously, from puberty onward

 | Only at/near ovulation, decades after being arrested

 |

### Hormonal control of gametogenesis — who acts on what

| **Hormone**

 | **Source**

 | **Target**

 | **Effect**

 |
| GnRH

 | HYPOTHALAMUS

 | Anterior pituitary

 | Triggers the whole cascade at puberty — stimulates LH and FSH secretion

 |
| LH

 | Anterior pituitary

 | LEYDIG cells (male)

 | Stimulates synthesis and secretion of ANDROGENS, which drive spermatogenesis

 |
| FSH

 | Anterior pituitary

 | SERTOLI cells (male)

 | Stimulates secretion of factors that help SPERMIOGENESIS

 |
| Androgens

 | Leydig cells

 | Seminiferous tubules and accessory ducts/glands

 | Drive spermatogenesis; maintain accessory duct and gland function

 |

### Male vs female reproductive system — side by side

| **Feature**

 | **Male**

 | **Female**

 |
| Primary sex organ

 | Testis — in the SCROTUM, outside the abdomen (needs 2–2.5°C cooler)

 | Ovary — inside the lower abdomen

 |
| Gamete production site

 | Seminiferous tubules

 | Ovarian follicles in the cortex

 |
| Nourishing cells

 | SERTOLI cells (inside the tubule)

 | GRANULOSA cells (surrounding the oocyte)

 |
| Hormone-secreting cells

 | LEYDIG/interstitial cells (outside the tubule) → androgens

 | Follicle and corpus luteum → estrogen and progesterone

 |
| Accessory ducts

 | Rete testis → vasa efferentia → epididymis → vas deferens → urethra

 | Fallopian tube (infundibulum → ampulla → isthmus) → uterus → vagina

 |
| Gametes produced per parent cell

 | 4 functional sperm

 | 1 functional ovum (+ polar bodies)

 |
| Timing

 | Starts at puberty, continues into old age

 | Oogonia fixed BEFORE birth; ceases around age 50

 |

### Why this matters for NEET

- High-value one-liners: Sertoli cells nourish germ cells, they do NOT secrete androgens
(Leydig cells do — a classic True/False NCERT exercise trap); spermatogonium (46) → secondary
spermatocyte (23, after meiosis I) → spermatid (23, after meiosis II, but 4 formed per primary
spermatocyte); oogenesis is unequal division (secondary oocyte keeps the cytoplasm, polar bodies
don't); oogonia are fixed for life — set before birth, unlike sperm made continuously.

- **Trap:** oogenesis's first meiotic division happens
**inside the tertiary follicle, at/near puberty** — NOT completed at the fetal stage
(only initiated then, then arrested in prophase I for years/decades). Don't confuse "oogenesis
starts in the fetus" with "oogenesis finishes in the fetus."

## Test Yourself: MCQs, PYQs & Active Recall

Answer these, then close the article and do an Active Recall. Reveal each answer only after you commit to one.

## Practice Questions

**Q1.** The scrotum maintains testicular temperature at:

- (a) The same as body temperature

- (b) 10°C lower than body temperature

- (c) 2–2.5°C lower than body temperature

- (d) 5°C higher than body temperature

**Answer: (c)** — The scrotum keeps testes 2–2.5°C cooler than internal body temperature, essential for spermatogenesis.

**Q2.** Inside a seminiferous tubule, nutrition to the dividing germ cells is provided by:

- (a) Spermatogonia

- (b) Sertoli cells

- (c) Leydig cells

- (d) Epididymal cells

**Answer: (b)** — Sertoli cells line the seminiferous tubule and nourish the germ cells; they do not secrete androgens.

**Q3.** Androgens are synthesised and secreted by:

- (a) Spermatogonia

- (b) Sertoli cells

- (c) Prostate gland

- (d) Leydig (interstitial) cells

**Answer: (d)** — Leydig or interstitial cells, located outside the seminiferous tubules, synthesise testicular androgens.

**Q4.** The correct path of sperm transport from the testis is:

- (a) Vasa efferentia → rete testis → epididymis → vas deferens

- (b) Vas deferens → epididymis → rete testis → vasa efferentia

- (c) Epididymis → rete testis → vasa efferentia → vas deferens

- (d) Rete testis → vasa efferentia → epididymis → vas deferens

**Answer: (d)** — Sperm travel: seminiferous tubule → rete testis → vasa efferentia → epididymis → vas deferens.

**Q5.** The site of fertilisation within the fallopian tube is the:

- (a) Infundibulum

- (b) Ampulla

- (c) Fimbriae

- (d) Isthmus

**Answer: (b)** — The ampulla, the wider part of the oviduct, is where fertilisation normally occurs.

**Q6.** The three layers of the uterine wall, from outside in, are:

- (a) Endometrium, myometrium, perimetrium

- (b) Perimetrium, endometrium, myometrium

- (c) Myometrium, perimetrium, endometrium

- (d) Perimetrium, myometrium, endometrium

**Answer: (d)** — From outside to inside: perimetrium (thin outer), myometrium (muscular), endometrium (inner glandular).

**Q7.** A primary spermatocyte, after the first meiotic division, forms:

- (a) Two diploid secondary spermatocytes

- (b) Four haploid spermatids

- (c) One diploid spermatogonium

- (d) Two haploid secondary spermatocytes with 23 chromosomes each

**Answer: (d)** — Meiosis I converts a diploid primary spermatocyte into two haploid secondary spermatocytes (23 chromosomes each).

**Q8.** The cap-like structure over the sperm head, filled with enzymes that aid fertilisation, is the:

- (a) Middle piece

- (b) Zona pellucida

- (c) Flagellum

- (d) Acrosome

**Answer: (d)** — The acrosome is the enzyme-filled cap over the anterior sperm head that helps penetrate the ovum.

**Q9.** For normal fertility, the minimum percentage of sperms that must show vigorous motility is:

- (a) 60%

- (b) 40%

- (c) 80%

- (d) 20%

**Answer: (b)** — At least 40% of ejaculated sperms must show vigorous motility for normal fertility (and at least 60% must have normal shape/size).

**Q10.** Oogonia in the human female are formed:

- (a) Only during menopause

- (b) Only during embryonic (fetal) development

- (c) Continuously throughout life

- (d) Only after puberty

**Answer: (b)** — Oogonia form only during fetal development; no new oogonia are added after birth.

**Q11.** The first meiotic division of the primary oocyte is completed:

- (a) In the fallopian tube after ovulation

- (b) During fetal development

- (c) Only after fertilisation

- (d) Inside the tertiary follicle, around puberty

**Answer: (d)** — Oogenesis is initiated in the fetus (arrested in prophase I), but meiosis I is only completed inside the tertiary follicle.

**Q12.** The unequal first meiotic division of the primary oocyte produces:

- (a) Two equal secondary oocytes

- (b) A secondary oocyte and a first polar body

- (c) Four equal ova

- (d) Two spermatids

**Answer: (b)** — This division is unequal: a large secondary oocyte (retaining most cytoplasm) and a tiny first polar body.

**Q13.** The cap-like structure marked A, which contains hydrolytic enzymes that help the sperm penetrate the egg membranes, is the

- (a) middle piece

- (b) centriole

- (c) perforatorium of the tail

- (d) acrosome

**Answer: (d)** — The acrosome is a cap over the anterior part of the nucleus, formed from the Golgi complex, and contains enzymes such as hyaluronidase that dissolve the egg coverings during fertilisation.

**Q14.** Numerous mitochondria, which supply the energy for sperm motility, are present in the part marked

- (a) E

- (b) D

- (c) C

- (d) A

**Answer: (b)** — D is the middle piece. It is packed with mitochondria that produce the ATP for the tail's movement.

**Q15.** The centrioles of the sperm are located in the part marked

- (a) B

- (b) E

- (c) C

- (d) D

**Answer: (c)** — C is the neck, which contains the proximal and distal centrioles; the distal centriole gives rise to the axial filament of the tail.

### NEET Previous Year Questions (PYQs)

*Real NEET previous-year questions on this chapter, with explanations in our own words.*

**Q16.** Which of the following statements is TRUE regarding Sertoli cells? (NEET PYQ)

- (a) They provide nutrition to germ cells

- (b) They are found outside the seminiferous tubule

- (c) They synthesise androgens

- (d) They form the acrosome

**Answer: (a)** — Sertoli cells nourish the dividing germ cells inside the seminiferous tubule; Leydig cells (outside the tubule) make androgens.

**Q17.** The number of primary follicles present in each human ovary at puberty is approximately: (NEET PYQ)

- (a) 6–10

- (b) 60,000–80,000

- (c) 2 million

- (d) 400

**Answer: (b)** — Most fetal follicles degenerate by puberty, leaving roughly 60,000–80,000 primary follicles per ovary.

**Q18.** FSH acts primarily on which cells to aid spermiogenesis? (NEET PYQ)

- (a) Leydig cells

- (b) Sertoli cells

- (c) Spermatogonia directly

- (d) Epididymal cells

**Answer: (b)** — FSH acts on Sertoli cells, stimulating secretion of factors that help spermiogenesis.

**Q19.** The site of production of the male gamete is the: (NEET PYQ)

- (a) Vas deferens

- (b) Prostate

- (c) Seminiferous tubule

- (d) Epididymis

**Answer: (c)** — Sperms are produced inside the seminiferous tubules of the testis.

**Q20.** A mature Graafian follicle releases the: (NEET PYQ)

- (a) Ootid

- (b) Secondary oocyte

- (c) Zygote

- (d) Primary oocyte

**Answer: (b)** — Ovulation releases the secondary oocyte (commonly called the ovum), not the primary oocyte.

**Q21.** Which structure surrounds the secondary oocyte after it forms? (NEET PYQ)

- (a) Chorionic villi

- (b) Corpus luteum

- (c) Zona pellucida

- (d) Endometrium

**Answer: (c)** — The zona pellucida is the new membrane that forms around the secondary oocyte.

### Active Recall Prompt

Write everything you can recall about **Human Reproduction (Part A)**, naming each part first: the **male reproductive system** (testis, scrotum, seminiferous tubule, Sertoli vs Leydig cells, sperm path, accessory glands); the **female reproductive system** (ovary, oviduct parts, uterine wall layers, mammary glands); **spermatogenesis** (spermatogonium → primary spermatocyte → secondary spermatocyte → spermatid → sperm, hormonal control, sperm structure); and **oogenesis** (oogonia, primary/secondary/tertiary/Graafian follicle, the unequal meiotic division, polar bodies). Begin each fact with its topic and end it with a full stop.