NDA Biology · Teaching notes
Reproduction — NDA Biology
Reproduction is a compact but high-concept NDA Biology chapter — 13 PYQs across 2020–2026, weighted toward the 'Apply' style where you have to trace a sequence or reason about chromosome numbers, not just recall a fact. The chapter teaches in four movements, building from why sexual reproduction exists up to the specific machinery of flowering plants and mammals: (1) Sexual reproduction and genetic principles — why two parents and meiosis create variation, and why chromosome number stays constant across generations; (2) Meiosis and DNA in flowering plants — where in the plant life cycle the DNA gets halved; (3) Angiosperm reproduction — flower parts, the pollen-tube pathway, double fertilisation (the 2n + n = 3n endosperm trick), and what each flower part becomes after fertilisation; (4) Animal and human reproduction — the male reproductive parts, the oestrus-vs-menstrual cycle, and how contraceptive pills work. Most marks turn on two recurring shapes: getting a SEQUENCE in the right order (pollen tube; egg to seed), and reasoning about PLOIDY (haploid gametes, diploid zygote, triploid endosperm). Master those two and the chapter is yours.
Subtopic notes
Sexual Reproduction — Why Two Parents and Meiosis
3 PYQsSexual reproduction mixes genetic material from two parents through meiosis (which makes varied haploid gametes) and fertilisation (which rejoins them) — the source of the variation that lets a species survive over evolutionary time.
Open note
Meiosis in Flowering Plants — Where the DNA Halves
1 PYQsIn a flowering plant the diploid DNA content is halved by meiosis during gamete formation — specifically when pollen (the male gamete) and the egg are made, not during seed germination, fruit formation, or bud formation.
Open note
Angiosperm Reproduction — Flower to Seed
7 PYQsIn flowering plants a pollen grain lands on the stigma, grows a tube down the style into the ovary, and delivers two male gametes — one fertilises the egg (→ diploid zygote → embryo → seed) and the other fuses with the polar nuclei (→ triploid endosperm), while the ovary itself becomes the fruit.
Open note
Animal and Human Reproduction — Cycles and Contraception
2 PYQsNon-primate female mammals run an oestrus cycle while primates (including humans) run a menstrual cycle; oral contraceptive pills prevent pregnancy by using hormones to inhibit ovulation (the release of the egg).
Open note
PYQ weightage by concept
13 concepts · 13 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
13 concepts · 13 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| The two engines of genetic variation — meiosis and fertilisation | 1 | 8% |
| Why variation is an evolutionary advantage | 1 | 8% |
| Why chromosome number stays constant across generations | 1 | 8% |
| Asexual vs sexual reproduction — one parent or twofoundation | — | — |
| Concept | PYQs | Share |
|---|---|---|
| DNA is halved during pollen (gamete) formation | 1 | 8% |
| Concept | PYQs | Share |
|---|---|---|
| The fertilisation-to-seed sequence: egg → zygote → embryo → seed | 2 | 15% |
| Flower structure and bisexual vs unisexual flowers | 1 | 8% |
| The pollen-tube pathway — stigma, style, ovary | 1 | 8% |
| Double fertilisation and the 2n + n = 3n endosperm | 1 | 8% |
| What each flower part becomes after fertilisation | 1 | 8% |
| Parts of the human male reproductive system | 1 | 8% |
| Concept | PYQs | Share |
|---|---|---|
| How oral contraceptive pills work — inhibiting ovulation | 1 | 8% |
| Oestrus cycle vs menstrual cycle — primates are different | 1 | 8% |
Formula & revision sheet
0 formulas · 2 reference tables · 14 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
0 formulas · 2 reference tables · 14 gotchas across all subtopics — the exam-eve cheat-sheet
Watch out for (4)
- Clones come from asexual reproduction, not sexual→ Asexual vs sexual reproduction — one parent or two
- Meiosis pairs with fertilisation — not mitosis, not conjugation→ The two engines of genetic variation — meiosis and fertilisation
- The advantage is variation, NOT more or 'healthier' offspring→ Why variation is an evolutionary advantage
- Constant, not decreasing — fertilisation undoes meiosis→ Why chromosome number stays constant across generations
Watch out for (1)
- Halving = gamete formation, not germination or fruiting→ DNA is halved during pollen (gamete) formation
Reference tables (2)
What each flower part becomes after fertilisation5 rows
| Flower part (before) | Becomes (after fertilisation) | Ploidy / note |
|---|---|---|
| Ovary | Fruit | The whole ovary wall ripens into the fruitQ |
| Ovule | Seed | Each fertilised ovule becomes one seed Ovary → fruit and ovule → seed are the two facts the bank tests most. |
| Zygote (2n) | Embryo | The embryo lies inside the seed |
| Secondary nucleus (2n) | Endosperm (3n) | Nutritive tissue feeding the embryo |
| Egg cell (n) | Zygote (2n) | After fusing with a male gamete |
Parts of the human male reproductive system5 rows
| Structure | System | Role |
|---|---|---|
| Testis | Male | Makes sperm and testosterone |
| Vas deferens | Male | Carries sperm from the testis |
| Seminal vesicle | Male | Gland; adds fluid to semen |
| Urethra | Male | Carries semen (and urine) out |
| Cervix | Female | Neck of the uterus — NOT a male partQ NDA 2020 — cervix is the odd one out: it belongs to the female reproductive system. |
Watch out for (7)
- Papaya is unisexual; hibiscus / mustard / sunflower are bisexual→ Flower structure and bisexual vs unisexual flowers
- Stigma comes first — not style, not pistil→ The pollen-tube pathway — stigma, style, ovary
- Both gametes fuse — the second does NOT degenerate→ Double fertilisation and the 2n + n = 3n endosperm
- Endosperm is 3n, zygote is 2n — don't swap them→ Double fertilisation and the 2n + n = 3n endosperm
- Ovary → fruit, ovule → seed — never the reverse→ What each flower part becomes after fertilisation
- Arrows point forward — embryo never comes before zygote→ The fertilisation-to-seed sequence: egg → zygote → embryo → seed
- Cervix is female — the classic 'odd one out'→ Parts of the human male reproductive system
Watch out for (2)
- They inhibit ovulation — they don't 'kill' anything→ How oral contraceptive pills work — inhibiting ovulation
- Primates have the MENSTRUAL cycle, not oestrus→ Oestrus cycle vs menstrual cycle — primates are different