Explore how plants reproduce sexually (through flowers, pollination, and fertilisation) and asexually (through vegetative reproduction), and how seeds are dispersed.
Asexual reproduction involves only one parent and produces offspring that are genetically identical to the parent — they are called clones. No gametes are involved. In plants, asexual reproduction is also called vegetative reproduction because it involves vegetative (non-reproductive) plant parts.
| Method | Plant Part Used | Example |
|---|---|---|
| Runner (stolon) | Horizontal stem along ground | Strawberry, spider plant |
| Bulb | Underground fleshy leaf bases storing food | Onion, tulip, daffodil |
| Tuber | Swollen underground stem storing food | Potato |
| Rhizome | Horizontal underground stem | Ginger, iris, couch grass |
| Cutting | Stem/leaf cut and rooted in soil | Geranium, rose |
| Grafting | One plant joined to rootstock of another | Apple, rose, grapevine |
Sexual reproduction involves the fusion of male and female gametes. The male gamete is contained in pollen; the female gamete is the egg cell within the ovule. Because gametes from different parents combine, the offspring are genetically varied — this is the raw material for evolution and adaptation.
Flowers are the reproductive organs of flowering plants (angiosperms). A typical flower has four whorls of parts:
Pollination is the transfer of pollen grains from the anther of one flower to the stigma of another (cross-pollination) or to the same flower (self-pollination). Two main agents carry pollen:
| Feature | Insect-Pollinated Flowers | Wind-Pollinated Flowers |
|---|---|---|
| Petals | Large, brightly coloured, scented | Small or absent, dull coloured |
| Nectaries | Present — produce nectar as reward | Absent |
| Pollen | Large, sticky, spiky — clings to insects | Tiny, light, smooth — easily airborne |
| Stigma | Small, sticky, inside flower | Large, feathery, hangs outside to catch pollen |
| Stamens | Inside flower, sheltered | Long filaments hanging outside flower |
| Examples | Roses, sunflowers, lavender | Grasses, maize, pine trees |
After a pollen grain lands on a compatible stigma, it germinates: a pollen tube grows down through the style, enters the ovary, and reaches the ovule. The male nucleus travels down the pollen tube and fuses with the egg cell inside the ovule. This fusion is fertilisation.
The zygote (fertilised egg) divides repeatedly by mitosis to form an embryo. The ovule develops into a seed (containing the embryo and a food store), and the ovary wall develops into the fruit.
Seeds must be dispersed (spread away from the parent plant) to reduce competition for light, water, and nutrients, and to colonise new areas. There are four main methods:
A seed is dormant — it contains an embryo and a food reserve (cotyledons) but will not grow until conditions are right. Three conditions are needed for germination:
| Feature | Asexual | Sexual |
|---|---|---|
| Number of parents | 1 | 2 (usually) |
| Genetic variation | None (clones) | Yes — offspring are unique |
| Speed | Fast | Slower |
| Gametes involved | No | Yes (pollen + egg cell) |
| Adaptability | Low — vulnerable to disease | High — can adapt to change |
| Energy cost | Low | High (flowers, nectar, fruit) |
| Temperature (°C) | Seeds germinated (out of 50) |
|---|---|
| 5 | 0 |
| 15 | 18 |
| 25 | 47 |
| 35 | 32 |
| 45 | 3 |