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Monday, 30 January 2017

Reproduction in organisms

1. Reproduction is the process of formation of young new individuals from the pre-existing grown up individuals of an organism. Reproduction is the means of perpetuation of race as   older individuals undergo senescence and die.

·   The period from birth to the natural death of an organism represents its life span. Life span of organisms varies from few days (Butterfly-1 to 2 weeks) to thousands of years (Banyan tree).

·  No individual is immortal except unicellular organism like amoeba that divides into two daughter organisms.

·  There is a cycle of birth, growth and death. Reproduction enables the continuity of species generation after generation.

·   When the offspring is produced by single parents with or without the involvement of gamete formation, the reproduction is called asexual reproduction.

·   When two parents (opposite sex) participates in reproduction process and also involves the fusion of male and female gametes, it is called sexual reproduction.

2. Asexual Reproduction

Single individual is capable of producing offspring which are identical and exact copy of their parent. The morphological and genetically individuals of same parents are called clone.
  • Asexual reproduction is common among single celled organisms, plants and animals with simple organization. 
  • In Protista and Monera, the parent cells divides into two to give rise to new individuals. Thus, in these organisms cell division is the mode of reproduction itself.
 3. Binary fission- in this method of asexual reproduction, a cell divides into two halves and rapidly grows into an adult. Ex- amoeba, paramecium.

 4. Budding- small buds are produced that remain attached initially with parents and get separated on maturation. Ex. Yeast.

  •  Fungi and simple plants like algae reproduce through special reproductive structures like zoospores (motile structure), conidia (penicillium), buds (hydra) and gemmules (sponges).
  • In plants, vegetative reproduction occurs by vegetative propagules like runner, rhizome, sucker, tuber, offset and bulb.
5. Water hyacinth is called ‘terror of Bengal’ because it one of the most invasive weeds found growing wherever there is standing water. It drains oxygen from the water which leads to death of fishes.
  • The ability of plants like potato, zinger, sugarcane, banana etc. has ability to produce roots from their nodes when come in contact of soil. This ability is used by gardeners and cultivators for commercial propagation.
  • Bryophyllum develops adventitious buds from notches present at margin of leaves.
  • Asexual reproduction is the most common method of reproduction in organisms having
  • simpler body like in algae and fungi but during unfavorable condition they shift to sexual reproduction.
6. Sexual Reproduction involves formation of male and female gametes, either by the same individual or different individuals of opposite sex. These gametes fuse to form zygote which develops to form the new organisms.
  • In sexual reproduction, fusion of male and female gametes results in offspring that are not identical to parents. after certain stage of growth and maturity in their life. This phase of growth is called juvenile phase. In plants it is known as vegetative phase. 
  • Some plants show flowering in particular season and some other flowers in all seasons. Some other plants like bamboo species flowers once in life time (after 50-100 years), 
  • Strobilanthus kunthiana flowers once in 12 years. 
  • The female placental animals exhibit cyclic change in activities ovaries and accessary glands as well as hormone during the reproductive phase.
  • In non-primate animals ( cow, sheep, rat, deer, dog, tiger etc.) cyclic change in females is called oestrus cycles and where as in primates ( monkey, apes, human beings) it is called menstrual cycle. 
  • Both in plants and animals, hormones are responsible for the transition between different phases of life cycle. Interaction between hormones and environmental factors regulate the reproductive processes.

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