2.1Unit 2 · Reproduction & Inheritance
Reproduction — Unit 2 — Edexcel IGCSE Biology Modular - UNIT 2 Revision Notes & Topical Questions
10 min read 4 parts Lesson 2 of 3 1 quiz
Lesson summary
Compare sexual and asexual reproduction.Human body cells are diploid (46 chromosomes); gametes are haploid (23 chromosomes).Seeds need water, oxygen and a suitable temperature to germinate; light is not needed.During germination, stored starch is broken down by amylase into sugar…
- Asexual reproduction in plants
- Sexual vs asexual
- Gametes and fertilisation
- Flower structure
- Adaptations for pollination
- Fertilisation in plants
Section 1 of 4Reproduction — Unit 2
Sexual vs asexual:
sexual reproduction needs gametes and fertilisation, producing genetically different offspring.- Asexual reproduction uses mitosis and one parent, so offspring are genetically identical.
- Asexual is quicker and needs no mate;
- sexual gives variation that can help a species survive changes such as new diseases.
Gametes and fertilisation:
- gametes are haploid, so when two fuse the zygote is diploid.
- In animals the gametes are sperm and egg;
- in flowering plants the male nucleus is in the pollen grain and the female nucleus is in the ovule.
Flower structure:
the male parts (stamen) are the anther, which makes pollen, and the filament.- The female parts (carpel) are the stigma, style and ovary containing ovules.
- Petals attract insects in insect-pollinated flowers; sepals protect the bud.
Adaptations for pollination:
- insect-pollinated flowers have colourful scented petals, nectar and sticky stigmas inside the flower.
- Wind-pollinated flowers have exposed anthers and feathery stigmas and produce huge amounts of light pollen.
Fertilisation in plants:
after pollination a pollen tube grows down the style to the ovule; the male nucleus fuses with the ovule nucleus.- The fertilised ovule becomes a seed containing an embryo and food store, and the ovary wall becomes the fruit, which helps dispersal.
Practical – conditions for germination:
set up tubes of cress seeds: one with water, air and warmth (control);- one dry;
- one with boiled cooled water covered with oil (no oxygen);
- one in a fridge.
- Only the control germinates well, showing water, oxygen and a suitable temperature are all needed.
Germinating seeds:
water activates enzymes; amylase breaks down stored starch into maltose/glucose, and proteases break proteins into amino acids.- These fuel respiration and growth until the seedling can photosynthesise.
- Dry mass therefore falls at first.
Asexual plant reproduction:
- strawberry plants send out runners that root and form new plants;
- potatoes grow from tubers.
- Gardeners take cuttings, dipping stems in rooting hormone, to produce many identical plants.
- strawberry plants send out runners that root and form new plants;
Human reproductive systems:
male – testes (make sperm and testosterone), scrotum, sperm duct, prostate gland and seminal vesicles (make fluid), urethra and penis.- Female – ovaries, oviducts (site of fertilisation), uterus (where the fetus develops), cervix and vagina.
- (release eggs, make oestrogen and progesterone)
- The placenta lets oxygen and nutrients diffuse to the fetus and carbon dioxide and urea to the mother;
- the amnion and amniotic fluid protect the fetus.
- Female – ovaries, oviducts (site of fertilisation), uterus (where the fetus develops), cervix and vagina.
Meiosis and gametes:
- Gametes are made by meiosis, which halves the chromosome number and produces genetically different cells.
- After fertilisation the zygote divides by mitosis to form an embryo.
Adaptations of gametes:
- Sperm have a tail to swim towards the egg and many mitochondria to release energy for movement.
- The egg cell is larger and has food stores in its cytoplasm to supply the early embryo.
Structure of a seed:
- A seed contains an embryo root, an embryo shoot, seed leaves (cotyledons) and a food store.
- The food store supplies the seedling until its leaves can photosynthesise.
Menstrual cycle:
The cycle lasts about 28 days.- If no egg is fertilised the uterus lining breaks down and is lost (menstruation, about days 1-5).
- The lining then thickens again, and an egg is released from an ovary (ovulation) at about day 14.
Oestrogen and progesterone:
Oestrogen from the ovaries rises during the first half of the cycle, causing the uterus lining to rebuild and thicken.- After ovulation progesterone rises and maintains the thick lining.
- When progesterone falls, the lining breaks down and menstruation begins.
FSH and LH:
Both are released by the pituitary gland.- FSH causes an egg to mature in a follicle and stimulates the ovary to make oestrogen.
- When oestrogen peaks, LH is released, which triggers ovulation and stimulates progesterone production.
Corpus luteum and pregnancy:
After ovulation the empty follicle becomes the corpus luteum, which secretes progesterone.- If there is no pregnancy it breaks down, progesterone falls and menstruation occurs.
- If pregnancy occurs it keeps making progesterone until the placenta takes over.
Placenta as an exchange surface:
Maternal and fetal blood come close but do not mix.- A large surface area and thin barrier allow efficient diffusion.
- The umbilical cord links the fetus to the placenta.
- The placenta blocks some harmful substances, but nicotine, alcohol and some viruses can cross it.
Female secondary sexual characteristics:
Controlled by oestrogen at pubertybreasts develop, hips widen, pubic and underarm hair grows and menstrual cycles begin.Male secondary sexual characteristics:
Controlled by testosterone at pubertyfacial and body hair grows, muscles develop, the voice deepens and the testes begin producing sperm.
Section 2 of 4Process & sequence
- Pollen lands on a stigma of the same species (pollination).
- A pollen tube grows out of the pollen grain, down through the style.
- The male nucleus travels down the pollen tube.
- The tube enters the ovule through the micropyle.
- The male nucleus fuses with the female nucleus in the ovule (fertilisation), forming a zygote.
- The ovule develops into a seed and the ovary into a fruit.
From pollination to seedwrite these steps in this order; each step is a marking point.
- Pollen lands on stigma
- Pollen tube grows down style
- Male nucleus enters ovule
- Nuclei fusezygote formed
- Ovule becomes seed
- Ovary becomes fruit
Section 3 of 4Compare
| Feature | Insect-pollinated | Wind-pollinated |
|---|---|---|
| Petals | Large, brightly coloured, scented | Small, dull or absent |
| Nectar | Present | Absent |
| Anthers | Inside flower, firmly attached | Hang outside flower on long filaments |
| Stigma | Small, sticky, inside flower | Large, feathery, outside flower |
| Pollen | Small amounts, larger, sticky or spiky | Large amounts, small, light and smooth |
| Feature | Sexual | Asexual |
|---|---|---|
| Number of parents | Two (usually) | One |
| Gametes | Yes | No |
| Offspring | Genetically varied | Genetically identical clones |
| Speed | Slower | Fast, many offspring |
| Advantage | Variation helps survive environmental change | No mate needed; good traits kept |
Section 4 of 4Worked examples
Explain why the dry mass of germinating seeds decreases during the first few days.
- Before leaves grow the seedling cannot photosynthesise.
- Stored starch is broken down to glucose, which is used in respiration to release energy for growth.
- Respiration converts glucose into carbon dioxide and water, which are lost, so dry mass falls until photosynthesis begins.
- Before leaves grow the seedling cannot photosynthesise.
Suggest one advantage and one disadvantage to a farmer of growing crops from cuttings.
- Advantage: all plants are genetically identical to a parent with desired features (e.g. high yield) and are produced quickly.
- Disadvantage: there is no genetic variation, so a single disease or change in conditions could affect the whole crop.
- Advantage: all plants are genetically identical to a parent with desired features (e.g. high yield) and are produced quickly.
Marked practiceQuizzes for this lesson
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🌳 Student Search Tree & Frequently Asked Exam Questions: reproduction
Step-by-step problem-solving guide, mark scheme criteria, and experimental error analysis curated by Dr. Khaled Dabour (DABOURHUB).
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1. Identify all given values and convert non-standard units, 2. State the primary formula or physiological/chemical principle, 3. Calculate to 3 significant figures and clearly state units.
Q2: What are the common mistakes and experimental sources of error for reproduction?
Avoid confusing independent vs dependent variables in practical questions. In calculation questions, double-check percentage change formula: (change / original) × 100.
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On DABOURHUB every reproduction question is grouped by syllabus point and shown with the mark-scheme wording, so you can see exactly which sentence earns the mark instead of scrolling through whole year papers.
What is the most common reproduction exam question and why do students lose marks on it?
The repeated pattern on Edexcel papers is a short stem that asks you to apply reproduction and then justify it with a command word (explain, suggest, compare). Marks are lost by stating the fact without linking it back to the wording of the question, so each reproduction item here is written as a full-mark answer.
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