CBSE Class 12 Biology: Human Reproduction — Complete Notes 2026

Male Reproductive System

• Testes: outside body (lower temperature needed for spermatogenesis); seminiferous tubules (sperm production) + Leydig cells (testosterone)
• Epididymis: sperm maturation and storage; vas deferens: transport to urethra
• Accessory glands: seminal vesicles (fructose, prostaglandins), prostate (enzymes), Cowper's gland (lubrication)

Spermatogenesis

• Spermatogonium (2n) → primary spermatocyte (2n) → meiosis I → 2 secondary spermatocytes (n) → meiosis II → 4 spermatids → spermiogenesis → 4 spermatozoa
• Sperm: head (acrosome with hydrolytic enzymes + nucleus), middle piece (mitochondria — 'powerhouse'), tail (flagellum)
• Sertoli cells: nurse cells; provide nutrition; Blood-Testis Barrier; secrete inhibin (negative feedback on FSH)

Female Reproductive System

• Ovaries: produce eggs; source of oestrogen and progesterone; follicles develop in cortex
• Fallopian tubes: fertilisation usually occurs here; fimbriae sweep egg from ovary; cilia move egg toward uterus
• Uterus: implantation; perimetrium (outer), myometrium (muscular), endometrium (inner — shed monthly)

Oogenesis

• Oogonium (2n) → primary oocyte (2n, arrested at prophase I since fetal stage) → triggered at puberty
• Meiosis I complete at ovulation → secondary oocyte (n) + first polar body; meiosis II complete after fertilisation
• Only one functional egg + 3 polar bodies (non-functional) from one primary oocyte — contrast with spermatogenesis

Menstrual Cycle

• Follicular phase: FSH stimulates follicle growth; oestrogen rises; endometrium proliferates (days 1–14)
• Ovulation: LH surge on day 13–14; Graafian follicle ruptures; egg released; corpus luteum forms
• Luteal phase: corpus luteum secretes progesterone; endometrium thickens; if no fertilisation, CL degenerates; menstruation

Fertilisation and Implantation

• Fertilisation: sperm penetrates secondary oocyte in fallopian tube; acrosome reaction releases enzymes
• Cortical reaction: release of cortical granules prevents polyspermy (zona reaction)
• Implantation: blastocyst implants in endometrium (day 6–7); trophoblast secretes HCG (maintains corpus luteum)

CBSE Board Focus

• Human Reproduction: 6–8 marks; spermatogenesis vs oogenesis comparison, menstrual cycle diagram
• Draw: T.S. testis (seminiferous tubule, Sertoli, Leydig cells), Graafian follicle with labelled parts
• Fertilisation mechanism: acrosome reaction, cortical reaction; role in preventing polyspermy — 3 marks