Sexual vs asexual reproduction
Sexual reproduction involves the fusion of the nuclei of two gametes to form a zygote, so the offspring show variation. Asexual reproduction needs one parent and no fusion of gametes; offspring are made by mitosis, so they are genetically identical clones with no variation. Sexual reproduction's variation helps a species survive change; asexual reproduction needs only one parent, is faster and keeps good features unchanged.
Pollination, fertilisation and seed formation
Pollination is the transfer of pollen from an anther to a stigma; fertilisation follows as the male gamete nucleus fuses with the egg nucleus in the ovule. The fertilised ovule becomes a seed and the ovary becomes a fruit. Insect-pollinated flowers have bright petals, nectar and sticky pollen; wind-pollinated flowers have small dull petals, a feathery stigma outside, and light smooth pollen. A seed germinates only with water, oxygen and warmth.
Menstrual hormones, placenta and amniotic fluid
In the menstrual cycle, oestrogen makes the uterus lining thicken after menstruation, and progesterone maintains the thick lining (its fall triggers menstruation); on 4SD0 you need only these two. The placenta exchanges substances between the mother's and fetus's blood without the bloods mixing — oxygen, glucose and antibodies pass to the fetus; carbon dioxide and urea pass back. The amniotic fluid is a shock absorber, not a food supply.
Drawn from real examiner reports.
Embryo forms by mitosis, not meiosis
Fertilisation is the fusion of a male gamete nucleus with a female gamete nucleus to form a zygote — not just 'the sperm meets the egg'. The zygote then grows into an embryo by MITOSIS (identical cells for growth), NOT meiosis (meiosis makes the gametes). Keep the spellings of mitosis and meiosis clearly different, or the examiner cannot tell which you mean.
"Identical" needs "genetically identical"
For asexual reproduction and cloning, 'the offspring are identical' is too vague to score. You must write 'genetically identical' or 'clones', referring to the genes — for example plant cloning from cuttings or runners gives genetically identical offspring. Plain 'identical' (same size, same look) does not earn the genetics mark.
Amniotic fluid protects; placenta feeds
The amniotic fluid is a shock absorber that protects the fetus from physical damage (bumps) — it does NOT supply food or oxygen. That is the placenta's job. A frequent marked error is to claim the amniotic fluid provides nutrients. Keep the two clear: the fluid cushions and protects; the placenta exchanges substances.
Placenta: name substances and direction
For placenta questions, vague answers like 'it passes nutrients and takes away waste' do not score. You must name the substances AND their direction: oxygen, glucose and antibodies pass from mother to fetus; carbon dioxide and urea pass from fetus to mother. Also state that this happens without the mother's and fetus's blood mixing.
Oestrogen builds, progesterone maintains
Keep the two menstrual-cycle hormones straight: oestrogen makes the uterus lining repair and build up / thicken; progesterone maintains the thickened lining, and its fall triggers menstruation. A common error is to swap them (saying oestrogen 'maintains' the lining). On 4SD0 only oestrogen and progesterone are needed.
Pollination ≠ fertilisation
These are two different steps in a fixed order. Pollination is the transfer of pollen from an anther to a stigma; it happens FIRST. Fertilisation is the later fusion of the male and female gamete nuclei inside the ovule. Writing that fertilisation is 'pollen landing on the stigma' confuses the two — that is pollination.
Pair each feature with its function
Reproduction questions reward linked answers, not lists. For 'explain how this flower is adapted for pollination', pair each feature with why it helps: 'the stigma is large and feathery, giving a big surface to catch wind-blown pollen'. Build each mark as feature + function.
Give precise two-element definitions
Define the key terms in their exact form: fertilisation = fusion of a male and female gamete nucleus to form a zygote; pollination = transfer of pollen from anther to stigma; asexual reproduction = one parent, genetically identical clones. Loose paraphrases lose the mark.
Do not over-answer with FSH/LH
On 4SD0 (and on Edexcel Paper 1) the detail of FSH and LH is NOT required — only oestrogen and progesterone in the menstrual cycle. Bringing in FSH/LH gains no marks and wastes time. Answer exactly what the question asks about the uterus lining.
Reproduction is how organisms produce new individuals. There are two types, and the exam wants precise, two-element definitions.
| Compare | Sexual reproduction | Asexual reproduction |
|---|---|---|
| Parents | Two | One |
| Gametes fuse? | Yes (fertilisation) | No |
| Offspring | Genetically different (variation) | Genetically identical (clones) |
| Main advantage | Variation aids survival / improvement | Fast; one parent; keeps good features |
Define asexual reproduction.
State two differences between sexual and asexual reproduction. (2 marks)
