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Organisms and Populations

Organisms and Populations PDF Notes, Important Questions and Synopsis


  • Ecology is a branch of biology which deals with the inter-relationships among organisms and interactions between organisms and their environment.

  • Homeostasis is a self-regulatory mechanism to maintain the internal environment constant despite changes in the external environment.

  • Regulators are organisms which maintain their homeostasis by physiological means to ensure constant body temperature and osmotic concentration irrespective of the fluctuations in the external environment; for example, birds and mammals.

  • Conformers are organisms which cannot maintain a constant internal environment; for example, fish and reptiles.

  • Adaptation is the development of certain features in an organism in response to a particular environment which may improve its chances of survival and reproduction in the habitat.

  • Differences between Hibernation and Aestivation

  • Population is defined as a group of organisms of the same kind at a particular time which occupy a particular space.

  • Population density is defined as the number of individuals present in a unit area at a given time.

  • Factors Affecting Population Density

  • Natality is the increase in the number of individuals in a population under the given environmental conditions.


  • Mortality is the loss of individuals due to death in a population under the given environmental conditions.

  • Age Pyramids for Human Population

  • Population growth can be measured as an increase in the size of a population over a period of time.

  • Population exhibits a characteristic pattern of increase known as the population growth curve.

  • Exponential (J-shaped) growth curve: When the resources are not limiting the growth, the plot is exponential (curve a).

  • Logistic (S-shaped) growth curve: When responses are limiting the growth, the plot is logistic (curve b).

  • The interaction of populations of two or more different species is known as population interaction.

  • Gauss gave the competitive exclusion principle which states that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually.

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NEET - Biology
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Asked by meenatoofansingh3 | 30 Apr, 2021, 04:14: PM
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