SS1 Biology Lesson Note on Reproduction

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REPRODUCTION

Reproduction is the ability of living organisms to produce offspring’s i.e. new individuals of their type. It is the only way in which each kind of organism can continue to live on forever although the individual must eventually die. The two forms of reproduction are sexual reproduction and asexual reproduction

ASEXUAL REPRODUCTION

In asexual reproduction, an individual produces an offspring by itself i.e. only one parent is present. There is no fusion of nuclei and the cells that give rise to the offspring usually divide by means of mitosis. As a result, asexual reproduction often produces clones-Offspring which are identical to the parent. In rare cases the offspring may not be identical due to mutation.

Asexual reproduction is common among simple organisms and flowering plants. Forms of asexual reproduction include the following:

• Fission: It is commonly found in Bacteria and Protists. The parent organism simply divides into two or more parts, each of which can exist by itself. e.g. binary fission in bacteria.
• Budding: In budding the offspring develops as an outgrowth of the parent. The bud may form on an internal or external surface of the parents. Internal buds are formed in some sponges and released when the parent dies. External buds occur in Hydra and Coral polyps. The buds break off from the parent without causing any injury and lead an independent life.

 

1. Spore Formation: Spore are small unicellular bodies which are produced in large numbers. They are small, light and easily dispersed by air. Under favourable conditions each spore can develop into an independent organism. Spores are commonly produced by Bacteria, Fungi, Protists, Algea, Mosses and Ferns.
2. Fragmentation: In this process a part of an organism breaks up or fragments from the parent organism and give rise to a new individual. It is a form of regeneration that occurs in simple organisms like algae, coelenterates and sponges.
3. Vegetative propagation: It occurs mainly in higher plants where a new plant grows from any portion of an old one other than the seeds. This is the formation of new individuals or plants by vegetative portion of the plant such as roots, stems and leaves. They are tubers, corns, bulbs, rhizomes, suckers and runners.
4. Root tubers are modified roots which grow under-ground and act as food storage organs. New plants may develop from buds which arise near the point of origin with the stem e.g. cassava, sweet potato and carrots.
5. Corns: These are modified underground stem which grow vertically. They produce lateral shoots which are capable of growing into new plants when detached e.g. cocoyam
6. Bulbs: There are modified underground leaves adapted for food storage. New bulbs in the axils of the scale leaves. Examples of bulbs are onions and lilies.
7. Parthenogenesis: This is the development of an egg without fertilization. It occurs in honey bee drones and aphids.

SEXUAL REPRODUCTION

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