Why plants reproduce
Reproduction is the process by which living organisms produce new individuals of their own kind. It allows a plant species to continue even after individual plants die.
Plants reproduce in two main ways:
asexual reproduction uses one parent and does not involve the fusion of reproductive cells,
sexual reproduction involves male and female reproductive cells and usually produces seeds.
Asexual reproduction
New plants formed asexually are usually very similar to the parent because they receive genetic material from only one parent.
Vegetative propagation
In vegetative propagation, a new plant grows from a root, stem or leaf instead of from a seed.
Plant part | Example | How a new plant begins |
|---|---|---|
Stem | potato | buds called eyes grow into shoots |
Underground stem | ginger | buds on the rhizome produce shoots |
Leaf | Bryophyllum | buds along leaf margins form plantlets |
Root | sweet potato | roots can give rise to new shoots |
Farmers and gardeners also use stem cuttings to grow plants such as rose and sugarcane. Vegetative propagation is fast and preserves useful features of the parent plant, but little variation is produced.
Budding, fragmentation and spores
In budding, a small outgrowth develops on the parent and separates when mature. Yeast reproduces this way.
In fragmentation, an organism breaks into pieces and each piece grows into a new individual. The alga Spirogyra is an example.
Spores are tiny reproductive bodies with protective coverings. Fungi such as bread mould form spores that can survive unfavourable conditions and travel through air.
The flower as a reproductive organ
A flower may contain four whorls:
sepals protect the flower bud,
petals may attract pollinators,
stamens are the male reproductive parts,
the pistil is the female reproductive part.
Each stamen has an anther, which makes pollen grains, and a filament that supports it. The pistil has a sticky stigma, a tube-like style, and an ovary containing one or more ovules.
A flower with both stamens and a pistil is bisexual. A flower with only stamens or only a pistil is unisexual.
Pollination and fertilisation
Pollination is the transfer of pollen from an anther to a stigma.
Self-pollination occurs when pollen reaches the stigma of the same flower or another flower on the same plant.
Cross-pollination occurs between flowers on different plants of the same kind.
Wind, water and animals such as insects can carry pollen. Bright petals, scent and nectar often help animal-pollinated flowers attract visitors.
After a compatible pollen grain lands on the stigma, it grows a pollen tube down through the style. The male reproductive cell travels through the tube to an ovule. The fusion of male and female reproductive cells is fertilisation, producing a zygote.
Pollination transfers pollen. Fertilisation is the later fusion of reproductive cells. They are not the same event.
Fruit, seed and dispersal
After fertilisation:
the zygote develops into an embryo,
the ovule develops into a seed,
the ovary develops into a fruit.
Seeds are dispersed away from the parent plant, reducing competition for light, water, minerals and space.
Method | Useful feature | Example |
|---|---|---|
Wind | light, winged or hairy seeds | cotton, drumstick |
Water | floating fruits or seeds | coconut |
Animals | hooks or edible fruits | Xanthium, guava |
Explosion | dry fruit splits suddenly | balsam, pea |
Summary
Asexual reproduction includes vegetative propagation, budding, fragmentation and spore formation.
Stamens produce pollen; the pistil contains stigma, style, ovary and ovules.
Pollination comes before fertilisation.
Ovules become seeds and the ovary becomes a fruit after fertilisation.