16.30610 · Section 16: Reproduction

Sexual reproduction in plants

Key learnings

Stamen and carpel — the two organs
Stamen = anther + filament. The anther produces and releases the pollen grains; the filament is the stalk that supports it and positions it for pollen transfer. Carpel = stigma + style + ovary. The stigma receives pollen, the style supports the stigma and is the route the pollen tube grows down, and the ovary contains the ovules. Around them, sepals protect the bud before it opens and petals attract insects with colour, scent and nectar.
Pollination first, then fertilisation
Pollination is the transfer of pollen grains from an anther to a stigma — a physical move, nothing more. Fertilisation comes later: the pollen grain germinates, a pollen tube grows down through the style and into the ovule (Extended), and the pollen nucleus fuses with a nucleus in that ovule. Then each fertilised ovule becomes a seed and the ovary becomes the fruit; the petals, sepals, stamens, stigma and style wither away.
Germination needs water, oxygen, warmth
Exactly three conditions. Water softens the seed coat, activates the enzymes that mobilise the food store and lets the embryo cells expand. Oxygen supports aerobic respiration, releasing the energy the embryo needs to grow. A suitable temperature keeps those enzymes near their optimum — too cold and reactions crawl, too hot and enzymes denature. Light is not on the list: the seed lives on its own stored food until the seedling emerges.

Common mistakes

Drawn from real examiner reports.

Pollination ≠ fertilisation

Pollination is pollen moving from an anther to a stigma. Fertilisation is the fusion of a pollen nucleus with a nucleus in the ovule, and it happens later, after the pollen tube has grown down the style. Writing "fertilisation is when pollen lands on the stigma" gives the definition of pollination and scores nothing. Two distinct, sequential events — never one.

Candidates defined fertilisation as pollen landing on the stigma (the definition of pollination); fertilisation is the fusion of the pollen nucleus with a nucleus in the ovule. (s23 Paper 13 Q28)

Wind-pollinated given insect features

Asked for wind-pollinated features, candidates describe bright petals, scent and nectar — every one of those is insect-pollinated. A wind-pollinated flower has small dull petals or none at all, a large feathery stigma hanging outside the flower, and anthers dangling outside on long filaments. Showy petals would be pointless when no pollinator is being attracted.

Candidates described nectar/colour features (insect-pollinated) instead of the feathery stigma, exposed anthers and light, smooth pollen of wind-pollinated flowers. (s22 Paper 31 Q6c; w22 Paper 32 Q7a)

Saying pollen is "light" is ambiguous

Examiners read "the pollen is light" as ambiguous — light in colour, or light in weight? Write "the pollen grains have a low mass". Wind-pollinated pollen is small, smooth and low in mass so it stays airborne, and is made in huge numbers because most grains never reach a stigma. Insect-pollinated pollen is larger, spiky or sticky, and made in far smaller numbers.

Candidates said pollen was "light" without specifying it referred to the pollen grains. (s22 Paper 31 Q6c)

Adding light to the germination list

The syllabus names exactly three conditions: water, oxygen and a suitable temperature. "Seeds need water, light and warmth" loses the mark. The confusion comes from photosynthesis — but a germinating seed runs on its stored food reserves and does not photosynthesise until the seedling has emerged above ground and opened its first leaves.

Ovary and ovule are not the same

The ovary is the whole chamber; the ovules are the separate structures inside it. After fertilisation each ovule becomes a seed and the ovary becomes the fruit around them. "The ovary becomes the seed" loses the mark, and on a diagram question labelling only the ovary — with no ovule marked inside it — throws away an easy label mark.

Stigma swapped with style

The stigma is the sticky or feathery tip that receives pollen. The style is the stalk beneath it that supports the stigma and that the pollen tube grows down through. Swapping the two is the commonest labelling error on a carpel diagram, and it also wrecks any description of the pollen tube route from stigma to ovule.

Self and cross judged backwards

Self-pollination (Extended) keeps pollen on one plant — same flower, or another on it. Cross-pollination reaches a different plant of the same species. Candidates then invert the consequences: self is reliable, needing no pollinator, but gives little variation; cross gives the variation a population needs to meet environmental change, yet needs insects or wind.

Exam tips

Name the structure, then its function
Never write "the male part". Name it — anther, filament, stigma, style, ovary, ovule — then give the mark-scheme verb: the anther produces pollen; the stigma receives pollen. Asked for the parts of a stamen, give both: anther and filament.
Write the whole chain, not the endpoints
Pollination → pollen tube grows down the style → pollen nucleus fuses with a nucleus in the ovule → ovule becomes the seed, ovary becomes the fruit. Jumping from "pollination happens" straight to "a seed forms" drops every mark in the middle of the chain.
Adaptation questions want the reason too
An "explain" question on wind- versus insect-pollination wants the feature and why it works: "feathery stigma — large surface area, so more airborne pollen is trapped". A bare list of features, however accurate, caps you well below full marks.
Self or cross? Trace the pollen first
Pin down where the pollen came from before you discuss genetics: same flower or same plant = self; a different plant of the same species = cross. Deciding the variation consequence first is how candidates end up arguing the wrong case in a scenario question.

Revision notes