Reproduction in Plants
ICSE Class 8 · Biology · Chapter 2
What this chapter covers
- What reproduction is and why it matters
- Types of asexual reproduction
- Vegetative propagation
- Artificial propagation by tissue culture
- Parts of a flower: a review
- Pollination: self and cross
- Agents of pollination
- Fertilisation
- Artificial pollination
Key points
- Reproduction produces new individuals of the same kind and keeps a species alive.
- Asexual reproduction needs one parent and gives identical offspring; sexual reproduction joins a male and a female gamete.
- Bacteria divide by binary fission, yeast and Hydra by budding, Spirogyra by fragmentation, and bread mould and ferns by spores.
- Vegetative propagation grows new plants from roots, stems or leaves, naturally (potato, ginger, grass, Bryophyllum) or artificially (cutting, layering, grafting, budding).
- Tissue culture grows thousands of identical, disease-free plantlets from a tiny piece of tissue on a nutrient medium, through a callus.
- A typical flower has four whorls: calyx, corolla, androecium (stamens) and gynoecium (carpels).
- Pollination moves pollen from anther to stigma; it is self-pollination within one plant and cross-pollination between two plants.
- Insect-pollinated flowers are bright, scented and have nectar and sticky pollen; wind-pollinated flowers are dull, with light pollen and feathery stigmas; water-pollinated flowers are small, with pollen that floats.
- In fertilisation, a pollen tube carries the male gamete to the ovule, where it fuses with the egg cell to form a zygote.
- After fertilisation the ovule becomes the seed and the ovary becomes the fruit.
- In artificial pollination, breeders emasculate, bag and hand-pollinate flowers to cross chosen parents.
Questions answered
Define reproduction. Why is it important for a species?
Reproduction is the process by which a living organism produces new individuals of its own kind. Without it, every kind of living thing would die out when its present members died.
Name the method of asexual reproduction in each: (a) yeast, (b) Spirogyra, (c) bacteria, (d) bread mould.
(a) budding, (b) fragmentation, (c) binary fission, (d) spore formation.
Why do spores have a thick wall?
The thick wall protects the spore from heat and dryness, so it can survive until it lands on a moist place with food.
Name the plant part used for vegetative propagation in (a) potato, (b) Bryophyllum, (c) sweet potato.
(a) stem tuber, with its eyes (buds), (b) leaf, from buds in the notches of its edge, (c) root.
Give two advantages and one disadvantage of vegetative propagation.
Advantages: plants grow and flower faster, and every new plant has the same good features as the parent. Disadvantage: all plants are identical, so one disease can destroy the whole crop.
What is a callus? Name two plants raised by tissue culture.
A callus is an unorganised mass of cells that forms when plant tissue grows on a nutrient medium. Banana and orchids are raised by tissue culture.
Name the four whorls of a flower and state which two are the essential whorls.
Calyx, corolla, androecium and gynoecium. The androecium and gynoecium are essential, because they produce the gametes.
Distinguish between self-pollination and cross-pollination.
In self-pollination, pollen reaches the stigma of the same flower or of another flower on the same plant. In cross-pollination, pollen reaches the stigma of a flower on a different plant of the same kind.