Reproduction · System
Flowers and pollination
A flower is not a decoration. It is a reproductive organ with a delivery problem: the gametes are in two places and the plant cannot move.
Start here
Grass has flowers. You have walked past millions of them without noticing.
So have oak, birch, hazel, wheat and rice. None of them has petals worth looking at, and every one of them flowers — which tells you something about what petals are actually for.
Why is it grass pollen that causes hay fever, and not rose pollen?
Because grass throws its pollen into the air and hopes. Wind carries nothing reliably, so a wind-pollinated plant compensates with quantity: light, smooth, dry grains released in enormous numbers, most of which land nowhere useful and some of which land in your nose. A rose hands its pollen to a bee. It makes a fraction as much, the grains are sticky rather than airborne, and almost none of it is ever loose in the air to breathe in. Hay fever is a side effect of one pollination strategy.
Match the job · nine parts
What is each part actually for?
0 of 9 checked
Pick a part, then choose its job. Every wrong option here is the right answer for a different part, so a guess still teaches you something.
Anther
Filament
Stigma
Style
Ovary
Ovule
Petal
Sepal
Nectary
Which job belongs to it?
CorrectNot this one — that job belongs to another part
Makes pollen grains, each carrying a male gamete nucleus.
Pollen grains are not gametes and it is worth being exact: each grain is a tough case carrying a nucleus that will become the male gamete. The anther’s whole job is manufacture and release — it splits open when the pollen is ready.
CorrectNot this one — that job belongs to another part
Holds the anther up and out, where pollen can be taken away.
A stalk, and position is everything. In an insect-pollinated flower it puts the anther exactly where a visiting insect must brush past it; in a wind-pollinated one it dangles the anther outside the flower where the wind can shake it.
CorrectNot this one — that job belongs to another part
A sticky or feathery surface that catches pollen grains.
The receiving surface, and its texture tells you how the pollen arrives. Sticky and small means pollen is being delivered by an animal; large and feathery means it is being fished out of moving air.
CorrectNot this one — that job belongs to another part
A stalk that raises the catching surface and gives the pollen tube its route down.
Two jobs in one stalk. It holds the stigma up where pollen will reach it, and once a grain has landed the pollen tube grows down through it to the ovary — which is the whole of the next lesson.
CorrectNot this one — that job belongs to another part
Contains the ovules, and becomes the fruit after fertilisation.
Note what it becomes. Every fruit you have ever eaten was the ovary of a flower, swollen after fertilisation — which is why a pea pod, a tomato and an apple are all fruits whatever a greengrocer calls them.
CorrectNot this one — that job belongs to another part
Contains a female gamete nucleus, and becomes the seed after fertilisation.
The female half of the pairing, and the one students most often confuse with the ovary that contains it. One ovule becomes one seed, so counting the seeds in a fruit tells you how many ovules were fertilised.
CorrectNot this one — that job belongs to another part
Attracts insects by colour and scent, and gives them a platform to land on.
An advertisement, not a reproductive organ — which is why the plants that need no advertising have no petals worth the name. Colour, pattern and scent are all aimed at a specific kind of visitor, and some patterns are only visible in ultraviolet light, which bees can see and we cannot.
CorrectNot this one — that job belongs to another part
Encloses and protects the whole flower while it is still a bud.
The small green flaps under the petals. Before the flower opened they were the outside of the bud, and everything delicate was folded up inside them.
CorrectNot this one — that job belongs to another part
Produces a sugary liquid that pays the visiting insect for its trouble.
Nectar is a real cost: the plant makes sugar by photosynthesis and then gives some of it away. It is worth it, because a paid courier that visits flower after flower of the same species delivers pollen far more reliably than the wind ever could.
Two solutions to one problem
Hire a courier, or throw it into the wind.
- PetalsLarge, coloured and often scented, with a platform to land on.Small, green or absent altogether. There is nobody to impress.
- NectarProduced in nectaries — the payment for the visit.None. Wind cannot be paid.
- PollenSticky or spiky so it clings to an insect. Made in modest amounts, because delivery is targeted.Smooth, light and dry so it drifts. Made in enormous amounts, because almost all of it is wasted.
- AnthersHeld inside the flower, positioned so a visiting insect must brush against them.Dangling outside on long thin filaments, where the slightest wind shakes the pollen loose.
- StigmaSmall and sticky, inside the flower where the insect will touch it.Large and feathery, hanging outside like a net to catch pollen from the air.
Key fact
Pollination is the transfer of pollen from an anther to a stigma. That is the whole definition. Nothing has yet fused, no gamete has met another, and the next lesson is about what happens after the pollen lands.
Think again
“Flowers are the pretty part of the plant.”
Flowers are reproductive organs, and every feature you find attractive about them is an advertisement aimed at something else. The colour is a signal to an animal with good colour vision. The scent is a signal to one that hunts by smell, often at night. The nectar is payment — a sugar solution the plant manufactures at real cost, purely to make the visit worth an insect’s time. Even the landing platform of a petal is engineering: it holds the insect in the position where the anthers will brush its back. None of it is aimed at us. It is worth noticing what follows from that, too — a plant that has no need to advertise does not bother, which is why grasses and most large trees have flowers so plain that most people have never recognised one.
“All flowers are pollinated by insects.”
Most of the plant material around you is wind-pollinated. Every grass, which includes wheat, rice, maize, barley and oats — so a large share of what the world eats — plus oak, beech, birch, hazel and most of the other big trees. These plants make flowers with no petals, no scent and no nectar, because there is nobody to attract. What they have instead is anthers dangling outside the flower on long thin filaments where the wind can shake them, feathery stigmas held out like nets to catch what drifts past, and pollen produced in quantities that make the second half of a June afternoon unbearable for anyone with hay fever. Both designs work. They simply pay for delivery in different currencies: one in sugar, the other in sheer number of grains.
Mastery ladder
Not started yet.
Rungs 3 and 4 you mark yourself.
Rung 1 · Define it precisely
Which of these is pollination?
Rung 2 · The one that catches people
A flower has no petals, no scent and no nectar, with anthers hanging outside on long filaments. What can you conclude?
Rung 3 · Name the parts and their jobs
Name the male and female parts of a flower and give the job of each. Then explain what pollination is, in one sentence, and say why the petals are not part of either group.
Rung 4 · Take it somewhere new
You are given two unlabelled flowers, one wind-pollinated and one insect-pollinated, and no other information. Describe three observations you would make to tell them apart, and explain what each observation tells you about how the pollen travels.
Key note
The male parts of a flower are the stamens: anther and filament. The female parts are the carpel: stigma, style, ovary and ovules. Pollen made in the anthers contains the male gamete nucleus; the ovules contain the female gamete nucleus. Pollination is the transfer of pollen from an anther to a stigma, by insect or by wind. Insect-pollinated flowers advertise and pay: coloured petals, scent, nectar, sticky pollen. Wind-pollinated flowers do neither: small dull flowers, exposed anthers, feathery stigmas, and vast amounts of light smooth pollen.
Going further
In 1862 Darwin was sent an orchid from Madagascar with a nectar spur nearly thirty centimetres long and the nectar at the very bottom of it. Any insect wanting that reward would have to reach the whole way down, and in doing so would be forced against the flower’s pollen. He published the obvious conclusion: there must be a moth in Madagascar with a tongue about thirty centimetres long, otherwise this flower could not be pollinated and would not exist. It was treated as an absurdity — one reviewer thought it showed how far the theory could be pushed. Forty-one years later, in 1903, a hawkmoth with a proboscis of the required length was collected in Madagascar and given the subspecies name praedicta, the predicted one. It was another ninety years before anyone actually filmed one feeding at the flower and confirmed the mechanism in full. That is the shape of a strong scientific claim: it is not merely consistent with what has been seen, it says in advance what must be found, and it can be shown wrong by anyone who looks and does not find it.
Before this lesson
- This follows on from Lifestyle and the developing foetus.
Connects to
At GCSE this becomes
- Plant reproduction in full, self- and cross-pollination, and pollination as an ecosystem service under threat.
Where to next
Ask Mr Badmus AI
Want to check which parts are male and which are female?
The flower described is a generalised one: many real flowers lack petals, sepals or nectaries, some carry only male or only female parts, and a few carry them on separate plants entirely.
Lesson content © MrBadmusAI.