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Organisms and Populations

Q1. What are euryhaline and stenohaline organisms?

Ans: The organism tolerating the high range of temperature is called eurythermal and the organism which can tolerate narrow range of temperature is called stenothermal.

Q2. What is homeostasis?

Ans: The ability of an organism to maintain the constancy of its internal environment despite varying external environmental conditions.

Q3. Mention any four major abiotic factors.

Ans: Temperature, water, light and soil.

Q4. State Allen's rule.

Ans: Mammals have shorter ears and limbs to minimize heat loss. This is called Allen's rule.

Q5. How humans are adapted to live in high altitude? Explain.


  • The people living in high altitudes compensate low oxygen by increasing production of red blood cells (RBCs).

  • The binding capacity of haemoglobin decreases and breathing rate increases.

  • People living at high altitudes of Himalayas have higher RBC count or total Hb than people living in plains.

Q6. Explain the factors that fluctuates the population growth / population density.


The population density can fluctuate due to the following reasons;

  1. Natality: It is the number of births during a given period of time. It increases the population density.

  2. Mortality: It is the number of deaths in a given time period. It decreases the population density.

  3. Immigration: It is the number of individuals of same species added to a habitat in a given time period. It increases the population density.

  4. Emigration: It is the number of individuals of same species that move to a different habitat in a given time period. It decreases the population density.

Q7. Explain the logistic growth model.


  • The logistic growth model can be seen when the resources become limited at certain point of time, so no population can grow exponentially.

  • This growth model is more realistic.

  • Every ecosystem or environment or habitat has limited resources to support a particular maximum number of individuals called its carrying capacity (K).

Q8. What are ectoparasites and endoparasites? List any three parasitic adaptations in animals.


Ectoparasites are the parasites which feed on the external surface of the host organism for food and shelter.

E.g., lice on humans, ticks on dogs, copepods, Cuscuta.

Endoparasites are the parasites which live inside the host's body at different sites like liver, kidney, lungs, etc., for food and shelter.

E.g., tapeworm, liver fluke, Plasmodium.

Adaptations of parasitic animals:

  • Loss of unnecessary sense organs.

  • Presence of adhesive organs or suckers.

  • Loss of digestive system.

  • High reproductive capacity.

Q9. What is commensalism? Explain by giving any four examples.

Ans: Commensalism is referred to as the interaction between two species where one species is benefited and the other is neither harmed nor benefited.


  • An orchid growing as an epiphyte on a mango tree. The orchid gets shelter and nutrition from mango tree while the mango tree is neither benefited nor harmed.

  • Barnacles growing on the back of whale. Barnacles are benefited to move to location for food as well as shelter while the whales are neither benefited nor harmed.

  • The egrets are in close association of grazing cattle. The cattle egrets are benefited by the cattle to detect insects because cattle stir up the bushes and insects are flushed out from the vegetation, to be detected by cattle egrets.

  • The commensalism is also found between sea anemones and the clown fish. The fish is protected from predators and sea anemones are neither benefited nor harmed.

Q10. Explain mutualism interaction by giving suitable examples.

Ans: Mutualism is referred to as the interspecific interaction in which both the interacting species are benefited.


  • Lichens represent close association between fungus and photosynthetic algae or cyanobacteria, where the fungus helps in the absorption of nutrients and provides protection while algae or cyanobacterium prepares the food.

  • Mycorrhizae are close mutual association between fungi and the roots of higher plants, where fungi help the plant for absorption of nutrients while the plant provides food for the fungus.

  • Mutualism are found in plant-animal relationships. Plants take the help of animals for pollination and dispersal of their seeds and animals are rewarded in the form of nectar or edible pollen or oviposition (site for laying egg).

  • Sexual deceit - The male bee pseudocopulates with it and during this process of pseudocopulation, the pollen grains are dusted on the body of male bees.

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