1. Sexual Reproduction in Plants: The Flower
Most flowering plants reproduce sexually, and the flower is the plant's reproductive structure. Just like animals, plants have separate male and female parts that produce sex cells (gametes).
Parts of a Flower
Key term: Ovule — the structure inside a plant's ovary that contains the female sex cell (egg cell) and develops into a seed after fertilisation.
2. Pollination: Getting Pollen to the Stigma
Pollination is the transfer of pollen from the anther of a flower to the stigma of a flower. It's important to know that pollination is NOT the same as fertilisation — pollination is just the pollen being transferred; fertilisation happens afterwards, when the male and female sex cells actually join.
Insect Pollination vs Wind Pollination
Plants have evolved very different flower designs depending on how they get pollinated.
Why the difference? Insect-pollinated flowers need to actively attract a pollinator, so they invest energy in bright colours, scent, and nectar. Wind-pollinated flowers don't need to attract anything — they rely on producing huge quantities of pollen to maximise the chance some of it randomly reaches another flower's stigma on the breeze.
3. Fertilisation and Seed Formation
Once a pollen grain lands on a compatible stigma, it grows a pollen tube down through the style and into the ovary. The male sex cell then travels down this tube and fuses with the female sex cell (egg cell) inside an ovule. This fusion is fertilisation.
Sequence: Pollination → Pollen tube growth → Fertilisation → Seed and fruit formation
After fertilisation:
1. The ovule develops into a seed, containing a tiny new plant embryo and a food store.
2. The ovary develops into a fruit, which surrounds and protects the seed(s).
3. The petals, sepals, and other flower parts usually wither and fall away, since they're no longer needed
Key term: Fruit — the structure that develops from a fertilised ovary, which contains and protects the seeds. Botanically, this includes many foods we call "vegetables," like tomatoes, cucumbers, and pea pods, because they develop from a flower's ovary.
4. Seed Dispersal: Spreading Seeds Away From the Parent Plant
Once seeds are formed, they need to be spread away from the parent plant. This is called seed dispersal, and it matters because seeds that land too close to the parent plant would have to compete with it for light, water, and nutrients — dispersal reduces this competition and helps the species colonise new areas.
5. Asexual Reproduction in Plants
Not all plant reproduction is sexual. Many plants can also reproduce asexually, producing new plants that are genetically identical to the parent (clones), without needing pollination or fertilisation at all.
Natural Methods
Artificial (Human-Controlled) Methods
Humans also use asexual reproduction deliberately, especially in farming and gardening — this is a form of vegetative propagation:
- Cuttings — a piece of stem is cut from a plant and placed in soil or water, where it grows its own roots and becomes a new, identical plant
- Grafting — a cutting (called a "scion") from one plant is attached to the rooted stem of another plant (the "rootstock"), often used to combine the fruit quality of one variety with the strong roots or disease resistance of another (common in apple and grape growing)
Advantage of asexual reproduction: Fast, reliable, and produces plants identical to a parent with known good qualities (e.g. a specific fruit flavour).
Disadvantage: No genetic variation is introduced, so if a disease or environmental change threatens the parent plant's characteristics, all the identical offspring are equally vulnerable.
6. Sexual vs Asexual Reproduction in Plants
7. Key Terms Glossary
1. Sepal: Protects the flower bud before it opens
2. Petal: Attracts pollinators (in insect-pollinated flowers)
3. Stamen: The male part of a flower (anther + filament)
4. Anther: Produces pollen
5. Carpel: The female part of a flower (stigma + style + ovary)
6. Stigma: Receives pollen during pollination
7. Ovary: Contains ovules; develops into a fruit after fertilisation
8. Ovule: Contains the female sex cell; develops into a seed after fertilisation
9. Pollination: The transfer of pollen from anther to stigma
10. Self-pollination: Pollination within the same plant
11. Cross-pollination: Pollination between two different plants of the same species
12. Fertilisation: The fusion of male and female sex cells
13. Seed: Develops from a fertilised ovule; contains a plant embryo
14. Fruit: Develops from a fertilised ovary; protects the seeds
15. Seed dispersal: The spreading of seeds away from the parent plant
16. Vegetative propagation: Asexual reproduction methods used or encouraged by humans (e.g. cuttings, grafting)
Frequently Asked Questions
Q: What is the difference between pollination and fertilisation?
A: Pollination is the transfer of pollen from the anther to the stigma, while fertilisation is the actual fusion of the male and female sex cells that happens afterwards, once the pollen tube has grown into the ovule.
Q: Why do some flowers not have brightly coloured petals?
A: Wind-pollinated flowers don't need to attract insects, so they don't invest energy in colourful, scented petals — they rely on producing huge amounts of light pollen instead.
Q: Is a tomato a fruit or a vegetable?
A: Botanically, a tomato is a fruit, because it develops from the fertilised ovary of a flower — the same is true of cucumbers, peppers, and pea pods, even though they're commonly called vegetables.
Q: Why is seed dispersal important?
A: It spreads seeds away from the parent plant, reducing competition for light, water, and nutrients, and helps the species spread into new areas.
Q: Can plants reproduce without flowers?
A: Yes — many plants reproduce asexually using runners, bulbs, tubers, or human-assisted methods like cuttings and grafting, without needing pollination or fertilisation at all.