Sexual reproduction in flowering plants
The stamen makes pollen; the pistil (carpel) holds ovules. After pollination and fertilisation, the ovule becomes a seed and the ovary becomes a fruit.
Parts of a flower
| Part | Job |
|---|---|
| Sepals | Green and leaf-like; protect the flower bud |
| Petals | Bright and often scented; attract insects for pollination |
| Stamen (anther + filament) | Male part; the anther makes pollen grains |
| Stigma (top of the carpel) | Sticky tip that receives pollen |
| Style (middle of the carpel) | Long tube through which the pollen tube grows |
| Ovary (base of the carpel) | Swollen part holding ovules; each ovule has an egg cell |
Unisexual vs bisexual flowers
From pollination to seed and fruit
**Pollination** is the transfer of pollen from the anther to the stigma. In **self-pollination**, pollen lands on the stigma of the same flower. In **cross-pollination**, it is carried to another flower by **wind, water or animals** such as insects and birds.
- 1Pollen lands on the sticky stigma.
- 2★A pollen tube grows out of the pollen grain, down through the style, to reach the ovule in the ovary.
- 3★The male germ cell moves down the tube and fuses with the female germ cell (egg) in the ovule: this is fertilisation.
- 4The fertilised egg, the zygote, divides many times to form an embryo inside the ovule.
- 5The ovule develops a tough coat and becomes a seed.
- 6The ovary grows and ripens into a fruit. The petals, sepals, stamens, style and stigma usually shrivel and fall off.
- 7With water, air and warmth, the seed germinates: the embryo grows into a seedling.
★ key step
Activity: parts of the embryo of a dicot seed
- 1Soak a few Bengal gram (chana) seeds in water overnight.
- 2Drain the water, cover the seeds with a wet cloth, and leave them for a day. Do not let them dry.
- 3Gently remove the seed coat and open a seed into its two halves.
- 4★Observe: two thick cotyledons (stored food), a tiny plumule (future shoot) and a radicle (future root).
- 5Gram is a dicot: its seed has two cotyledons.
★ key step
How to draw the flower and the pollen tube
- Draw a stalk with green sepals at the base and petals above them.
- In the centre, draw the flask-shaped pistil (carpel): a swollen ovary at the base with round ovules inside, a long style, and a knob-like stigma on top.
- Around the carpel, draw two or three stamens, each with a thin filament and an oval anther on top.
- For germination of pollen on the stigma: draw a pollen grain on the stigma, a pollen tube running down the style into the ovary, the male germ cell in the tube, and the female germ cell in the ovule.
- Label every part with straight lines.
When you eat a mango, the juicy part is the ripened ovary and the stone holds the seed. Honeybees moving across a mustard field carry pollen from flower to flower: that is cross-pollination.
2 marks: “Distinguish between self-pollination and cross-pollination.” Self: pollen reaches the stigma of the same flower. Cross: pollen is carried to the stigma of another flower by wind, water or animals.
3 marks: “List the changes that take place in a flower after fertilisation.” Zygote → embryo; ovule → seed with a tough coat; ovary → fruit; petals, sepals, stamens, style and stigma shrivel and fall.
5 marks: “Draw a longitudinal section of a flower and label its reproductive parts. Describe how fertilisation takes place.” Labelled stamen (anther, filament) and carpel (stigma, style, ovary, ovule); pollination; pollen tube through the style; fusion of male germ cell and egg; zygote.
Stamen is the pollen-maker (male); carpel is the cradle for ovules (female). After fertilisation the two O's grow up: ovule → seed, ovary → fruit.