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.
Every subtopic, worked example, formula and trap in one printable document — answers shown, ready to share.
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