EC2 ExcelLoading…
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).
State the THREE conditions needed for seed germination. Is light one of them?
State two differences between sexual reproduction and asexual reproduction. (2 marks)