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CBSE Class 12th Biology Notes for Chapter 13 Organisms And Populations

           Chapter 13 Organisms And Populations

  • Ecology is the study of the relationships of living organisms with the abiotic and biotic components of their environment. It is concerned with four levels of biological organization- organisms, populations, communities and biomes.


  • Important physical factors which affect how organisms adapt:
    • Temperature
    • Light
    • Water
    • Soil


  • Evolutionary changes through natural selection occur at population level. A population is a group of individuals of a given species sharing or competing for similar resources in a defined geographical area.


  • Ecological effect of any factors on a population is generally reflected in its size.


  • Population grows through births and immigration and decline through deaths and emigration.


  • Depending on the outcome, interactions between two species are classified as:
    • Competition: Both species suffer
    • Predation and parasitism: One benefits and the other suffers
    • Commensalism: One benefits and the other is unaffected
    • Amensalism: One is harmed, other unaffected
    • Mutualism: Both species benefit


  • Predation is a very important process through which the trophic energy transfer is facilitated and some predators help in controlling their prey populations.

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