Phenotypic adaptation involves changes in the body of an organism in response to  mutation orcertain 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 thermoregulators.


NCERT Points To Remember 


☆Adaptation 

Any attribute of organism (morphological, physiological, behavioural ) that enable them to survive and reproduce in its habitat.

  1. Morphological 

  • Many desert plants have no leaves a thick cuticle on their leaf surfaces and have their stomata arranged in deep pits ( sunken ) to minimise water loss through transpiration. They also have photosynthetic pathway (CAM ) that enables their stomata to remain closed during day time. Some desert plants like Opuntia, have no leaves -- they are reduced to spines-- and the photosynthetic function is taken over by the stems or (photosynthesis is done by flattened stem).

2. Physiological 

  • Kangaroo rat in north American desert is capable of meeting all its water requirement through its internal fat oxidation  ( in which water is a  by product ) in the absence of an external source of water.
  • Antifreezing protein in fishes enable them to survive below 0°C temperature in Antarctica.
  • Mammals from colder climates generally have shorter ears and limbs to minimise heat loss. ( This is called the Allen's rule ). In polar seas aquatic mammals like seals have a thick layer of fat ( blubber ) below their skin that acts as an insulator and reduces loss of body heat.
                         

3. Behavioural Adaptation 

  • Desert lizards lack the physiological ability that mammals have to deal with the high temperatures of their habitat, but manage to keep their body temperature fairly constant by behavioural means. They bask in the sun and absorb heat when their body temperature drops below the comfort zone, but move into shade when the ambient temperature increasing. 


♧ Actotherm -- The organism which uses external source to regulate body temperature is called Actotherm.

♧ Endotherm -- The organism which are independent to external source to regulate body temperature is called Endotherm.