- Life span is the period from birth to the natural death of an organism.
- After the death of living organisms also, the population is maintained by the process of reproduction.
- Reproduction is the biological process by which an organism produces its offspring similar to itself.
- The offspring grows, matures and in turn produces new offspring.
- By the process of reproduction, all living organisms maintain their population and ensure the continuity of species.
- Reproduction is of two types- 1) asexual reproduction 2) sexual reproduction.
ASEXUAL REPRODUCTION
- The offspring is produced by single parent without the fusion of gametes.
- A single parent produces offspring and the off springs are exact copies of their parents.
- The off springs are genetically and morphologically similar - clones.
- Common in unicellular organisms, and plants and animals of relatively simple organisation.
- A single parent is involved and so no fusion of gametes.
- Only mitosis takes place.
- Rapid multiplication.
- fission- the parent body divides in to two equal halves and each half grows in to an adult -- binary fission
- Budding- small bud is produced due to the cell division at one particular site -- remains attached initially to the parent cell --grows -- gets separated -- matures into a new individual.
- Members of kingdom fungi and simple plants reproduce through special reproductive microscopic motile structures called as zoospores.
- Example- chlamydomonas
- Other common structures are conidia in Penicillium,
- buds in Hydra,
- gemmules in sponge
Modes of asexual reproduction
Example- Amoeba.
Dividing plane-
Transverse, eg paramoecium, planaria
Longitudinal, euglena
When nucleus divides multiple times and forms multiple cells - multiple fission
Example- yeast
Fragmentation
Body divides into several parts -- each part develop into a independent complete organism.
Eg. Planaria, hydra, starfish, spirogyra (green algae), fungus.
Asexual reproductive structures-
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