Pollination and Fertilisation in Plants

Pollination — Core

Pollination is the transfer of pollen grains from an anther to a stigma. That’s the entire definition — it says nothing about what happens next, because pollination reaching a stigma doesn’t guarantee that fertilisation will follow. A pollen grain still has to germinate and grow a pollen tube down to an ovule before nuclei actually fuse. Keep the sequence straight: anther, pollen transfer, stigma, pollen tube, fertilisation.

Insect-pollinated flowers — Core

An insect-pollinated flower is built to attract a visiting insect and load it with pollen. Typical adaptations include large or brightly coloured petals, scent or nectar that draws insects in, anthers positioned so a visiting insect brushes against them, and a sticky stigma that catches pollen already carried on an insect’s body. Insect-pollinated pollen tends to be relatively large, heavy and sticky or textured, so it clings to an insect’s body rather than falling straight off — and because transfer is targeted rather than random, insect-pollinated flowers can get away with producing comparatively few pollen grains.

Wind-pollinated flowers — Core

A wind-pollinated flower has no insect to attract, so its structure solves a completely different problem: releasing pollen into moving air and catching whatever pollen is already airborne. Petals are usually small and dull, and scent or nectar is unnecessary. Anthers are exposed, often hanging loosely on long filaments so that wind can shake pollen free easily, and stigmas are large, exposed and often feathery, which gives them a large surface area for intercepting airborne pollen. Because wind transfer is essentially undirected, wind-pollinated flowers compensate by producing huge numbers of small, light, smooth pollen grains — sheer volume standing in for the targeting that insects would otherwise provide.

Don’t just list these adaptations — connect each one to its consequence. A feathery stigma matters because it gives a larger surface area for trapping airborne pollen; large numbers of pollen grains matter because any single grain has a low probability of actually reaching a suitable stigma. That connective reasoning is usually where the second mark sits, not just the first.

Fertilisation in a flowering plant — Core

Fertilisation in a flowering plant is the fusion of a pollen nucleus with a nucleus in an ovule. It happens after the pollen tube has reached the ovule, not at the moment pollen lands on the stigma. Keeping the locations straight helps: pollen is made at the anther, received at the stigma, and it’s the ovary — specifically an ovule inside it — where the nuclei actually fuse.

Self-pollination and cross-pollination — Supplement

Self-pollination is the transfer of pollen from an anther to a stigma of the same flower, or of a different flower on the same plant. Cross-pollination is the transfer of pollen from an anther of one plant to a stigma of a different plant of the same species. The distinction that matters is simply whether the pollen stays on the same plant or moves to another one — not whether two separate flowers are involved, since self-pollination can perfectly well happen between two flowers on one plant.

Self-pollination tends to produce less genetic variation, because the genetic material combining at fertilisation is drawn from a single individual. What it offers instead is reproductive assurance — a plant isn’t dependent on a pollinator or a neighbouring plant of the same species actually being available. Cross-pollination combines genetic material from two separate plants and so tends to produce greater variation, which gives a population a wider range of characteristics to draw on if the environment changes — but only if pollen actually completes the journey between plants, so cross-pollination depends more heavily on an effective transfer mechanism such as insects or wind.

One boundary worth holding onto here: self-pollination is still sexual reproduction, because gamete nuclei still fuse. It doesn’t make the offspring clones in the way asexual reproduction does — the genetic material has still been combined through fertilisation, just from a narrower genetic pool than cross-pollination draws on.

Pollen tube growth and fertilisation — Supplement

Once a compatible pollen grain lands on a stigma, it germinates and grows a pollen tube, which extends down through the style towards an ovule inside the ovary. The pollen nucleus travels down through this tube, and when the tube reaches the ovule, the pollen nucleus fuses with a nucleus inside it — that fusion is fertilisation. Precision matters in how you phrase this: it is the pollen tube that grows, and the pollen nucleus that travels down it — the whole pollen grain does not travel down the tube itself.

Cambridge’s current specification stops there. Endosperm production and the detailed development of the seed after fertilisation are not required at this stage, so keep this page’s scope at fertilisation itself rather than what happens to the seed afterwards.

Where this leads next

Fertilisation is the biological event that makes a seed capable of germinating — but a fertilised seed still needs specific external conditions before that growth actually resumes, covered on seed germination.