Plant Reproduction
Describe the structure of a flower and explain the processes of wind and insect pollination, fertilisation, seed and fruit formation, and seed dispersal in plants
What a learner can do afterwards
- Identifies the anther as the pollen-producing part, the sepal as the bud-protecting part, and the carpel as a female reproductive part
- Compares wind-pollinated and insect-pollinated flowers and explains adaptations of each
- Traces the journey from pollination to seed dispersal
- Identifies and explains at least two methods of seed dispersal
1 · Read
You have learned how pollination can lead to seeds. A complete flower has sepals, petals, stamens and one or more carpels. Sepals protect the unopened bud. Petals often attract insects. A stamen is a male reproductive part. It has a filament supporting an anther, where pollen is made. Some flowers lack one or more of these groups of parts.
A carpel is a female reproductive part. Its stigma receives pollen. Its style leads to an ovary that holds one or more ovules. Each ovule contains an egg cell. A flower may have one carpel or several.
Pollination transfers pollen from an anther to a stigma. This can happen within one flower or between flowers of the same species. Compatible pollen can grow a tube through the style to an ovule. Sperm cells travel along the tube. During fertilisation, a sperm nucleus fuses with the egg cell's nucleus inside the ovule. A nucleus contains a cell's genetic information. Pollen arriving does not guarantee fertilisation or seed development.
Pollination is pollen transfer. Fertilisation is the joining of sperm and egg nuclei inside an ovule.
Grass flowers use wind pollination. They usually have small or no petals, no nectar or scent, and lots of light pollen. Exposed anthers release pollen; feathery stigmas catch it. Many insect-pollinated flowers use colour, scent or nectar to attract visitors. Nectar is sugary food. Pollen can stick to an insect's body and reach a stigma on a later visit. These are common patterns, not features of every species.
An insect visiting for nectar may also carry pollen.
After fertilisation, an ovule can develop into a seed containing an embryo, a young plant. The ovary usually develops into a fruit around the seeds. Fruit may be dry or fleshy. Seed dispersal moves seeds away from the parent, sometimes inside a fruit. This can reduce competition for light, water and space. Dispersal does not guarantee a suitable place to grow.
Wind can carry light seeds or fruits with wings or fluff. Water can carry floating fruits. Hooks on some fruits catch on animal fur, so the seeds inside travel with the animal. Animals may also eat fruit and later pass undigested seeds in droppings. Some dry pods burst and scatter seeds. Match the moving seed or fruit to the feature that helps it travel.
The fruit attaches to fur. Its seeds travel inside it.
Pollination transfers pollen to a stigma. Fertilisation joins sperm and egg nuclei. Ovules can become seeds, the ovary usually becomes fruit, and dispersal moves seeds away.
The flower reproduction lesson, question repairs and revised flashcards were written for this dataset. Textbook records were consulted for scientific facts, without adapting their wording.
Five readings were written for this dataset. Linked videos: How bees help plants have sex - Fernanda S. Valdovinos, and The beautiful tricks of flowers - Jonathan Drori, catalogued as TED-Ed resources. Video rights remain with their publishers.
More to read
Identify a flower part by its job
A flower-part description can give you two clues: where a structure is and what it does. If a thin filament supports a pollen-producing structure, that structure is the anther. Together, filament and anther form a stamen.
The pollen-receiving surface is the stigma. Follow the style beneath it towards the ovary. The ovules are inside the ovary, and an egg cell is inside each ovule. These structures belong to a carpel.
Sepals protect a closed bud. Petals often attract insect visitors. A complete flower has sepals, petals, stamens and carpels. Missing one of these groups makes a flower incomplete. Having several carpels does not make a flower incomplete.
What does pollen on a stigma prove?
Finding pollen on a stigma is evidence of pollination. It is not evidence that fertilisation has already happened or that a seed will develop.
For fertilisation to follow, compatible pollen must grow a tube towards an ovule. Sperm cells travel along this tube. Inside the ovule, a sperm nucleus can fuse with the egg cell's nucleus. That fusion is fertilisation.
Pollen may reach a stigma in the same flower, another flower on the same plant, or a flower on a different plant of the same species. Wind or an insect can transport the pollen. Neither carrier performs the fusion inside the ovule.
When explaining an observation, name the event you observed. A pollen grain arriving and two nuclei fusing are different events.
An ovary can hold several future seeds
An ovary may contain several ovules. Each ovule contains an egg cell. After fertilisation, an ovule can develop into a seed containing an embryo, the young plant. The surrounding ovary usually develops into fruit.
This explains how one fruit can contain several seeds. The fruit and its seeds did not all develop from one ovule. Separate ovules developed into the separate seeds. An ovule that does not complete development will not produce a mature seed.
A fruit need not be sweet or soft. Fruits can be dry. A winged fruit may carry a seed through the air, while a fleshy fruit may be eaten by an animal. The seed is distinct from the fruit carrying it.
The same carrier can move different material
Wind can carry pollen between flowers. It can also carry a light fruit with a seed inside. These journeys have different roles. Pollen reaching a stigma is pollination. Moving a seed away from its parent is seed dispersal.
Animals can also take part at different stages. An insect feeding at flowers may transfer pollen on its body. An animal carrying a hooked fruit on its fur moves seeds that have already formed. Animals that eat fruit may later pass undigested seeds in their droppings.
To identify the process, first check what moves. Then check where it goes. Naming the carrier alone does not distinguish pollination from seed dispersal.
Dispersal changes where a seed might grow
A seedling growing beneath its parent may compete with it for light, water and space. Dispersal can move a seed elsewhere and reduce that competition.
Different features help different journeys. Wings or fluff help light seeds or fruits travel in moving air. Hooks attach fruits to fur. Floating fruits can travel with moving water. Some dry pods split open suddenly and scatter their seeds.
None of these features chooses a suitable landing place for every seed. A fruit may be carried away and still land where its seed cannot grow. Reaching a new place, germinating and surviving are separate outcomes. Germination means beginning to grow; dispersal does not guarantee it.
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