Biology Class 12 NCERT Solutions: Chapter 13 Organisms and Populations Part 1 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Q. 1 How is diapause different from hibernation?


  • Diapause is a stage of suspended development to cope with unfavorable conditions.
  • Many species of Zooplankton and insects exhibit diapause to tide over adverse climatic conditions during their development.
  • Hibernation or winter sleep is a resting stage where in animals escape winters (cold) by hiding themselves in their shelters.
  • They escape the winter season by entering a state of inactivity by slowing their metabolism.
  • The phenomenon of hibernation is exhibited by bats, squirrels, and other rodents.
Diapause V/S Hibernation

Q. 2 If a marine fish is placed in a fresh water aquarium, will the fish be able to survive? Why or why not?


  • If a marine fish is placed in a fresh water aquarium, then its chances of survival will diminish.
  • This is because their bodies are adapted to high salt concentrations of the marine environment. In fresh water conditions, they are unable to regulate the water entering their body (through osmosis) .
  • Water enters their body due to the hypotonic environment outside.
  • This results in the swelling up of the body, eventually leading to the death of the marine fish.

Q. 3 Define phenotypic adaptation. Give one example.


  • Phenotypic adaptation involves changes in the body of an organism in response to genetic mutation or certain environmental changes.
  • These responsive adjustments occur in an organism in order to cope with environmental conditions present in their natural habitats.
  • For example, desert plants have thick cuticles and sunken stomata on the surface of their leaves to prevent transpiration.
  • Similarly, elephants have long ears that act as thermo regulators.

Q. 4 Most living organisms cannot survive at temperature above . How are some microbes able to live in habitats with temperatures exceeding ?


  • Archaebacteria (Thermophiles) are ancient forms of bacteria found in hot water springs and deep sea hydrothermal vents.
  • They are able to survive in high temperatures (which far exceed ) because their bodies have adapted to such environmental conditions.
  • These organisms contain specialized thermo-resistant enzymes, which carry out metabolic functions that do not get destroyed at such high temperatures.

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