Reproduction
Learn Reproduction with notes, examples, and practice questions.
Chapter Overview
Sexual reproduction creates genetic variation through meiosis and fertilisation — the raw material for evolution.
Reproduction ensures continuity of life. Class 12 covers sexual reproduction in flowering plants and humans, menstrual cycle, gametogenesis, and reproductive health — high-scoring NEET and board topics.
Sexual Reproduction in Flowering Plants
Pollen grain
Male gametophyte — 2 male gametes in pollen tube
Embryo sac
7-celled, 8-nucleate (Polygonum type)
- Stamen (androecium) = male; carpel (gynoecium) = female
- Pollination: self vs cross; agents — wind, water, insects
- Double fertilisation: syngamy + triple fusion → zygote + endosperm (unique to angiosperms)
- Post-fertilisation: ovule → seed; ovary → fruit
Human Reproduction
- Male: testes → seminiferous tubules → spermatogenesis
- Female: ovaries → graafian follicle → oogenesis
- Placenta: exchange organ between mother and foetus; secretes hCG, progesterone
- Parturition: foetal ejection reflex + oxytocin
Menstrual Cycle (~28 days)
- Follicular phase: FSH → follicle growth; oestrogen rises
- Ovulation (~day 14): LH surge
- Luteal phase: corpus luteum → progesterone; if no pregnancy, menstruation
Reproductive Health
- Contraception: barrier, IUD, hormonal pills, surgical (vasectomy/tubectomy)
- STDs: AIDS (HIV), gonorrhoea, syphilis — prevention and awareness
- ART: IVF, ZIFT, GIFT — test-tube baby technology
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
Example 1: Double Fertilisation
Name the two events in double fertilisation in angiosperms.
- 1Syngamy: one male gamete + egg → diploid zygote (2n).
- 2Triple fusion: second male gamete + two polar nuclei → triploid primary endosperm nucleus (3n).
Answer
Syngamy + triple fusion
Example 2: Hormone in Ovulation
Which hormone triggers ovulation?
- 1LH surge mid-cycle causes follicle rupture and egg release.
Answer
Luteinising hormone (LH)
Example 3: Placenta Function
List two functions of placenta.
- 1Nutrient and gas exchange
- 2Secretes hormones (hCG, progesterone, oestrogen)
Answer
Exchange + endocrine support
Key Points to Remember
- ✓ Angiosperms: double fertilisation is defining feature
- ✓ Spermatogenesis continuous from puberty; oogenesis has long arrest phases
- ✓ Know labelled diagrams: TS anther, embryo sac, human reproductive system
- ✓ MTP legal up to certain gestation period in India — know ethics context
Exam Tips
- • Draw embryo sac with labels for 3-mark questions
- • Link hormones to menstrual cycle phases in tabular form
- • Differentiate microsporogenesis vs megasporogenesis
Formula Cheat Sheet
Quick reference — NCERT board exam formulas
Plant Reproduction
- Double fertilisation:Syngamy (male gamete + egg → zygote 2n) + triple fusion (male gamete + polar nuclei → PEN 3n)
- Pollen grain:Haploid male gametophyte — 2 male gametes in pollen tube
- Embryo sac:7-celled, 8-nucleate (Polygonum type)
- Post-fertilisation: ovule → seed ; ovary → fruit
Human Reproduction & Cycle
- Spermatogenesis:Seminiferous tubules of testes ; continuous from puberty
- Oogenesis:Graafian follicle in ovary ; arrested phases in development
- Ovulation:Triggered by LH surge (~day 14 of 28-day cycle)
- Luteal phase:Corpus luteum → progesterone ; maintains uterine lining
- Placenta:Foetal-maternal exchange ; secretes hCG, progesterone, oestrogen
Practice MCQs — Reproduction
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
Double fertilisation occurs in: