(a) (i) A relatively constant internal (within the body) environment permits all biochemical reaction and physiological function to proceed with maximum efficiency and, thus, enhance the overall 'fitness' of the species. Hence, the living system always tends to remain in a steady state with the help of a self-regulatory mechanism. Such a phenomenon, which involves the maintenance of a constant internal environments, is known as homeostasis.
(ii) Regulate : Maintain homeostasis by ensuring constant body temperature (thermoregulation) and constant osmotic concentration (osmoregulation).
(iii) Conform : Change the internal environments with the external environment.
(b) Living organisms cope with stressful external environmental conditions in many ways, such as :
(i) Regulate : Maintain homeostasis by ensuring constant body temperature (thermoregulation) and constant osmotic concentration (osmoregulation).
Example : Mammals regulate body temperature by shivering in cold and sweating in heat.
(ii) Conform : The internal environment of conformers changes with the external environment.
Example : In aquatic animals, the osmotic concentration of the body fluids changes with that the ambient water osmotic concentration.
(iii) Migrate : Some organisms move from a stressful habitat to a hospitable area temporarily and return when the stressful period is over.
Example : Every winter, migratory birds come from Siberia to Keoladeo National Park, Rajasthan.
(iv) Suspend : In higher plants, seeds and some other vegetative reproductive structures serve as means to tide over periods of stress besides helping in dispersal-they germinate to form new plants under favourable moisture and temperature conditions.
