Edexcel International GCSE Biology 4BI1: Reproduction – Revision Notes

For full explanations and worked examples, use the study guide. These notes condense sub-topic 3(a), Reproduction (points 3.1–3.13), of the Pearson Edexcel International GCSE Biology (4BI1) specification, Issue 3, for the June and November series examined under Issue 3. The course is untiered. Point 3.10B is bold with a B reference and is examined on Paper 2 only.

When you are ready, test yourself with the practice questions. The Topic 3 revision notes cover inheritance as well, and the Topic 3 practice set has more questions. The course hub is Edexcel IGCSE Biology and the printable checklist lists every point.

Key definitions

Term	Definition
Sexual reproduction	Fusion of male and female gametes; offspring genetically different
Asexual reproduction	One parent, no gametes, mitosis; offspring genetically identical (clones)
Gamete	Sex cell: sperm and egg in humans; male nucleus in pollen and female nucleus in ovule in plants
Fertilisation	Fusion of a male and a female gamete (their nuclei)
Zygote	The single cell formed at fertilisation; divides to form an embryo
Pollination	Transfer of pollen from an anther to a stigma
Germination	Growth of a seed into a seedling
Ovulation	Release of an egg from an ovary
Menstruation	Breakdown and loss of the uterus lining

3.1–3.2 Sexual vs asexual

	Sexual	Asexual
Number of parents	Usually two	One
Gametes and fertilisation	Yes	No
Variation	Yes	No (clones)
Speed	Slower	Faster
Survives a change in conditions	Some offspring may	All offspring equally at risk

Zygote → divides by mitosis → ball of cells → embryo.

3.3 Flowers

Male part: stamen = anther + filament. Female part: carpel = stigma + style + ovary (with ovules).

	Insect-pollinated	Wind-pollinated
Petals	Large, bright, scented	Small, green or absent
Nectar	Yes	No
Anthers	Inside flower	Outside, on long filaments
Stigma	Inside, sticky	Outside, large, feathery
Pollen	Larger, sticky or spiky, less	Small, light, smooth, lots

Method in steps: an “adaptation” answer

1. Name the feature (“anthers hang outside the flower”).
2. Say what it does (“pollen is shaken out by the wind”).
3. Link to pollination (“so pollen is carried to other flowers”).

3.4 Seed and fruit formation

Pollen lands on stigma → pollen tube grows down style → enters ovule → male nucleus fuses with female nucleus → zygote → embryo.

Before	After fertilisation
Ovule	Seed
Ovary	Fruit
Zygote	Embryo plant

3.5 Germination practical

Needed: water, oxygen, suitable temperature. Light is not usually needed.

Condition	Why it is needed
Water	Activates enzymes; seed swells and the coat splits
Oxygen	Aerobic respiration releases energy for growth
Warmth	Enzymes work at a useful rate (too cold: slow; too hot: denatured)

Method in steps: a fair germination test

1. Change one condition only (the independent variable).
2. Keep the same species, number of seeds, volume of water, time and other conditions.
3. Count seeds with a visible root after a set time.
4. Calculate percentage germination = (number germinated ÷ number set up) × 100.
5. Repeat and find a mean.

Small reminder: 26 of 40 seeds germinate → (26 ÷ 40) × 100 = 65%.

3.6 Food reserves in germination

Stores in cotyledons or endosperm → enzymes digest them:

Store	Enzyme	Product	Used for
Starch	Amylase	Maltose → glucose	Respiration; cellulose for cell walls
Protein	Protease	Amino acids	New proteins for growth
Lipid	Lipase	Fatty acids and glycerol	Respiration; membranes

Dry mass: falls at first (stored food respired, no photosynthesis yet) → rises once leaves photosynthesise faster than the seedling respires.

Method in steps: explaining a dry mass graph

1. Describe the shape with numbers from the graph (falls from day 0 to the lowest point, then rises).
2. Explain the fall: stored starch is broken down to glucose and respired; carbon dioxide is lost.
3. State why it is not replaced: no leaves yet, so no photosynthesis.
4. Explain the rise: leaves photosynthesise; glucose is made faster than it is respired, so new tissue is built.

Small reminder: dry mass 1.50 g → 1.26 g. Change = (1.26 − 1.50) ÷ 1.50 × 100 = −16% (a 16% decrease).

3.7 Asexual reproduction in plants

• Runners (natural): side stems along the soil (strawberry); new plants form where roots grow; genetically identical to the parent.
• Cuttings (artificial): cut shoot below a node → remove lower leaves (less transpiration) → rooting powder (plant hormones) → damp compost, covered to keep humid.

Small reminder: 18 of 24 cuttings root → (18 ÷ 24) × 100 = 75%.

3.8 Reproductive systems

Male	Function
Testes (in scrotum)	Sperm and testosterone; cooler outside the body
Sperm duct	Carries sperm to the urethra
Glands	Add fluid with nutrients → semen
Urethra / penis	Carry semen out; penis places it in the vagina

Female	Function
Ovary	Eggs; oestrogen and progesterone
Oviduct	Cilia move egg; site of fertilisation
Uterus	Lining for implantation; muscular wall for birth
Cervix	Ring of muscle; keeps fetus in; widens at birth
Vagina	Receives sperm; birth canal

3.9 and 3.10B The menstrual cycle

Hormone	Made in	Role	Paper
Oestrogen	Ovary	Repairs and thickens the uterus lining (days 5–14)	1 and 2
Progesterone	Ovary (corpus luteum)	Maintains the lining (days 14–28)	1 and 2
FSH	Pituitary gland	Egg matures in follicle; stimulates oestrogen production	Paper 2 only
LH	Pituitary gland	Surge triggers ovulation (about day 14); forms corpus luteum	Paper 2 only

Timeline (about 28 days): days 1–5 menstruation → repair → ovulation about day 14 → maintenance → progesterone falls → menstruation.

Paper 2 only feedback: oestrogen inhibits FSH and stimulates LH; progesterone inhibits FSH and LH.

Method in steps: reading a hormone graph

1. Find the day of the oestrogen peak: ovulation follows soon after.
2. Match each rise to its effect: oestrogen rising → lining thickening; progesterone high → lining kept.
3. Find where progesterone falls: menstruation follows.
4. (Paper 2 only) Look for the sharp LH peak just before ovulation, and the FSH rise at the start of the cycle.

If an embryo implants, progesterone stays high, the lining is kept, and there is no menstruation.

3.11–3.12 Placenta and amniotic fluid

Placenta: blood of mother and embryo does not mix. Diffusion across a thin barrier.

• Mother → embryo: glucose, amino acids, fatty acids, minerals, vitamins, water, oxygen.
• Embryo → mother: carbon dioxide, urea.
• Adaptations: large surface area (villi), thin barrier, rich blood supply on both sides.

Small reminder, a two-mark explanation: “The placenta has many villi, which give a large surface area [1], so more glucose and oxygen diffuse into the embryo’s blood per second [1].”

Amniotic fluid: shock absorber; supports and cushions the embryo against knocks; lets it move.

3.13 Secondary sexual characteristics

Testosterone (testes)	Oestrogen (ovaries)
Sperm production begins	Menstrual cycle begins
Facial and body hair	Breasts develop
Voice deepens	Hips widen
Muscles develop

Pubic and underarm hair grow in both sexes at puberty.

Must-know distinctions

• Pollination vs fertilisation: pollen moved vs nuclei fused.
• Ovule vs ovary: ovule → seed; ovary → fruit.
• Oestrogen vs progesterone: repairs and thickens vs maintains.
• FSH vs LH (Paper 2 only): egg matures vs egg released.
• Runners vs cuttings: natural vs artificial; both give clones.
• Dry mass vs fresh mass: dry mass shows food use; fresh mass is distorted by water uptake.

Quick self-test

1. Define pollination.
2. Give two features of a wind-pollinated stigma.
3. What does the ovary become after fertilisation?
4. Name the three conditions a seed needs to germinate.
5. Which enzyme breaks down starch in a germinating seed, and what is the glucose used for?
6. Why does the dry mass of a seedling fall during the first few days?
7. Why are the lower leaves removed from a cutting?
8. Give the function of the cilia in the oviduct.
9. Which hormone maintains the uterus lining?
10. (Paper 2 only) Which hormone triggers ovulation, and where is it made?
11. Name two substances that pass from embryo to mother across the placenta.
12. 30 out of 48 seeds germinate. Calculate the percentage germination.

Answers

1. Transfer of pollen from an anther to a stigma.
2. Large/feathery; hangs outside the flower.
3. The fruit.
4. Water, oxygen, a suitable temperature.
5. Amylase; respiration (and making cellulose).
6. Stored food is respired and the seedling cannot yet photosynthesise.
7. To reduce water loss by transpiration.
8. Sweep the egg towards the uterus.
9. Progesterone.
10. LH; the pituitary gland.
11. Carbon dioxide and urea.
12. (30 ÷ 48) × 100 = 62.5%.

Where marks are usually lost

• Writing “pollen joins the egg” for fertilisation instead of “male nucleus fuses with female nucleus”.
• Giving a flower feature without explaining how it helps pollination.
• Stating that the ovary becomes the seed.
• Leaving out oxygen, or adding light, in the list of germination conditions.
• Saying germinating seeds lose mass because “they use energy”, without naming respiration of stored food.
• Not keeping all but one variable the same when designing a germination test.
• Mixing up oestrogen (repair) and progesterone (maintain).
• Saying FSH or LH comes from the ovary (Paper 2 only content).
• Saying mother’s and embryo’s blood mix in the placenta.
• Calling cuttings a natural method.

Official syllabus

Pearson Edexcel International GCSE in Biology (4BI1) specification, Issue 3, first examination June 2019, Pearson Education Limited – Topic 3, Reproduction and inheritance, sub-topic (a) Reproduction.