Sexual vs asexual reproduction
Sexual reproduction: two parents; a male gamete (sperm or pollen) fuses with a female gamete (egg) at fertilisation, forming a zygote that divides by mitosis into an embryo. Gametes are made by meiosis, so offspring show genetic variation. Asexual reproduction: one parent, mitosis only, no gametes; offspring are genetically identical clones (strawberry runners = natural; cuttings = artificial) — fast and needing no mate, but all share the same vulnerabilities.
Flowering-plant reproduction
Insect-pollinated flowers: colourful petals, scent, nectar, sticky/spiky pollen, anthers and stigma inside. Wind-pollinated: no petals, scent or nectar; much light, smooth pollen; feathery stigmas outside. After pollination a pollen tube grows down the style and the male nucleus fuses with the egg in the ovule — the ovule becomes a seed, the ovary wall the fruit. Germination needs water, warmth and oxygen (NOT light); germination rate = (number germinated ÷ total) × 100%.
Human reproduction
Testes make sperm by meiosis and testosterone; ovaries make egg cells by meiosis (fertilisation occurs in the oviduct). Menstrual cycle: oestrogen thickens/repairs the uterus lining; progesterone (corpus luteum) maintains it — without fertilisation it falls and menstruation begins. Placenta: exchange without the two bloods mixing — glucose, oxygen and antibodies pass mother to fetus; carbon dioxide and urea fetus to mother. Amniotic fluid is a shock absorber.
Drawn from real examiner reports.
Name placenta substances and direction
On placenta questions, "nutrients and waste pass across" scores nothing — name specific substances AND direction. Glucose, oxygen, amino acids and antibodies diffuse from mother to fetus; carbon dioxide and urea diffuse from fetus to mother. The maternal and fetal blood supplies do NOT mix; exchange is by diffusion across the thin villi.
June 2024 Paper 2B Q4(b): vague "nutrients/waste" for the placenta did not score. (Digest: section 3a.)
Amniotic fluid does not feed the fetus
Amniotic fluid does NOT feed the fetus — supplying glucose and oxygen is the placenta's job. Its role is purely mechanical: a shock absorber protecting the fetus from physical damage (knocks and bumps). Saying it provides nutrients or oxygen is penalised, and vague "protects the baby" earns nothing — say shock absorber against physical damage.
June 2024 Paper 2B Q4(b): describing amniotic fluid as a nutrient-transfer medium was explicitly penalised. (Digest: section 3a.)
Meiosis makes gametes, not the embryo
The commonest reproduction error is saying meiosis produces the embryo. Correct sequence: gametes formed by MEIOSIS → fertilisation → zygote → the zygote divides by MITOSIS repeatedly → embryo. Meiosis halves the chromosome number (46 → 23); fusing two haploid gametes restores diploid 46; every division that builds the embryo is mitosis.
June 2023 Paper 1BR Q7(b)(i): candidates saying meiosis produces the embryo was a reported common error. (Digest: section 3a.)
Pollination is not fertilisation
Two separate stages. Pollination is the transfer of pollen from an anther to a stigma — no cell fusion yet. Fertilisation is the fusion of the male nucleus (delivered down the pollen tube) with the egg cell nucleus in the ovule. A flower can be pollinated without being fertilised, so do not use the two words interchangeably.
Germination does not need light
Seeds germinate with only three conditions — water (activates enzymes, softens the testa), warmth (for enzyme reactions) and oxygen (for aerobic respiration). Light is NOT required; a seed germinates in the dark. Light is only needed AFTER germination, once the seedling has leaves for photosynthesis. Listing light as a condition loses the mark.
Oestrogen repairs, progesterone maintains
In the menstrual cycle, oestrogen (from the follicle) makes the uterus lining thicken and repair after menstruation; progesterone (from the corpus luteum) maintains it ready for implantation. Reversing them — progesterone repairs or oestrogen maintains — loses the marks. If no fertilisation occurs, progesterone falls and the lining breaks down.
June 2023 Paper 1BR Q7(a)(ii): oestrogen repairs the uterus lining and progesterone maintains it; reversing the two roles was a reported error. (Digest: section 2j, menstrual-cycle hormones.)
Adaptation answers: feature, job, outcome
For "how is this structure adapted for its function": name the feature → say what it does → link to the outcome. E.g. a feathery stigma outside the flower gives a large surface area to catch wind-blown pollen, raising pollination chances. A bare feature list scores nothing.
Match the command word
State or name wants the term only; describe wants steps or features; explain wants a reason (a "because"); calculate wants working and a value. On germination-rate or IVF data, do not just quote figures — manipulate them, give a direction of change, then a biological reason.
Answer only what is asked (Paper 1)
FSH and LH (statement 3.10B) are emboldened and examined only on Paper 2B, not Paper 1BR. If a Paper 1 question asks how oestrogen or progesterone acts on the uterus lining, answer only that — adding FSH/LH detail earns no marks and wastes time you need elsewhere.
Sexual reproduction — reproduction involving the fusion of two gametes (one from each parent) at fertilisation, producing a zygote that develops by mitosis into an embryo. Offspring show genetic variation because gametes are produced by meiosis and random fertilisation mixes alleles.
Asexual reproduction — reproduction from one parent only, involving mitosis, producing genetically identical offspring (clones). No gametes or fertilisation involved.
Gametes — sex cells with a haploid (half) chromosome number produced by meiosis. In humans: sperm (male) and egg cells/ova (female). In flowering plants: pollen (male) and egg cells in the ovule (female).
Fertilisation — the fusion of a male and a female gamete to form a diploid zygote.
Germination — the resumption of growth of a seed; requires water, warmth and oxygen (NOT light).
What are the TWO key differences between sexual and asexual reproduction?
State two differences between sexual reproduction and asexual reproduction. (2 marks)
