🌷 Reproduction in Plants
1. Flowering plants undergo sexual reproduction to produce offspring that are genetically different from their parents.
2. The flower is the reproductive part of a flowering plant.
1. Male parts:
- Anther — found at the tip of the filament; produces and stores pollen grains. Each pollen grain contains the male reproductive cell.
- Filament — holds the anther up to release pollen grains.
2. Female parts:
- Stigma — found at the tip of the style; receives pollen grains during pollination.
- Style — connects the stigma to the ovary and holds the stigma up to receive pollen grains.
- Ovary — contains the ovules (some flowers have only one ovule in one ovary); develops into a fruit after pollination and fertilisation.
- Ovule — contains the female reproductive cell; it is the site where fertilisation occurs, and it develops into a seed after pollination and fertilisation.
1. Pollination is the transfer of pollen grains from the anther to the stigma.
- Self-pollination — occurs within the same flower or between flowers of the same plant.
- Cross-pollination — occurs between flowers from different plants of the same species.
1. Characteristics:
- (a) large and brightly-coloured petals,
- (b) scented to attract pollinators,
- (c) have nectar to attract pollinators,
- (d) anthers and stigmas are within the flower (they do not hang out), so the flower relies on animals entering it,
- (e) stigmas are usually sticky, and
- (f) pollen grains are rough and sticky to stick to pollinators more easily.
2. How it works:
- When a pollinator (such as a bee) collects nectar from a flower, pollen grains from the anther attach to its legs and body.
- When the animal visits another flower of the same species, the pollen grains are transferred to the stigma — thus pollinating the flower.
1. Characteristics:
- (a) flowers are usually small and dull-coloured,
- (b) scentless and have no nectar,
- (c) the anthers hang out of the flower to increase the chances of pollen grains being carried away by the wind, and
- (d) the large and feathery stigmas hang out of the flower to increase the chances of receiving pollen grains carried by the wind.
2. Pollen grains are smooth and light so they can be carried further by the wind.
1. After a pollen grain lands on the stigma, it produces a narrow tube called the pollen tube, which grows down the style towards the ovary.
2. When the pollen tube reaches the ovule inside the ovary, it releases the male reproductive cell, which travels down the pollen tube to fuse with the female reproductive cell in the ovule.
3. The fusion of the male and female reproductive cells is known as fertilisation.
Pollination = transfer of pollen grains from the anther to the stigma. Fertilisation = fusion of the male and female reproductive cells in the ovule. Pollination happens first, then fertilisation.
Ovary → swells and develops into a fruit.
Ovule → develops into a seed.
Petals, anther, filament, stigma and style → wither and drop off.
1. Seed dispersal is the movement or transport of seeds away from the parent plant.
2. Plants disperse their seeds to:
- (a) avoid overcrowding, and
- (b) reduce competition between the young and parent plants for nutrients / mineral salts, water, light and space.
3. Plants disperse their fruits and seeds in four main ways: by water, wind, splitting or animals.
| Method | How it works | Examples |
|---|---|---|
| By water | Fibrous husk traps air so the fruit floats; waterproof outer covering prevents sinking. Greater speed of water flow → further dispersal. | coconut, pong pong, mangrove, lotus, nipah palm (attap) |
| By wind | Light seeds with wing-like or hair-like structures stay afloat longer and are carried further. Greater speed of wind → further dispersal. | wing-like: maple, shorea, angsana hair-like: dandelion, lallang |
| By splitting | Pod-like structure splits open along a seam when dry to release seeds; some split with explosive force and scatter seeds further; others release seeds with hair- or wing-like structures that the wind then carries away. | pea plant, rubber plant, balsam (explosive) kapok, African tulip (wind-carried) |
| By animals | Sweet juicy flesh attracts animals to eat the fruit — large seeds are thrown away; small indigestible seeds pass out in waste further away and the waste feeds the seedling; hooks attach to fur or feathers of passing animals and brush off elsewhere. Greater number of animals → more seeds dispersed. | mango, avocado (thrown away) papaya, apple, berries (eaten & passed out) burdock, love grass, mimosa (hooks) |