Write a short note on:
$(a)$ Adaptations of desert plants and animals
$(b)$ Adaptations of plants to water scarcity
$(c)$ Behavioural adaptations in animals
$(d)$ Importance of light to plants
$(e)$ Effect of temperature or water scarcity and the adaptations of animals.

(N/A) Adaptations of desert plants and animals
Adaptations of desert plants: Plants in deserts are adapted to water scarcity and heat. They have extensive root systems to reach underground water,thick cuticles,and sunken stomata to reduce transpiration. In $Opuntia$,leaves are modified into spines,and photosynthesis occurs in green stems. They use $CAM$ ($Crassulacean$ $Acid$ $Metabolism$) pathway to keep stomata closed during the day.
Adaptations of desert animals: Animals like kangaroo rats,lizards,and snakes are well-adapted. The kangaroo rat never drinks water; it concentrates its urine to conserve water. Desert lizards bask in the sun during the morning and burrow in the sand during the afternoon to escape heat.
$(b)$ Adaptations of plants to water scarcity: Plants adapt by developing deep root systems,thick waxy cuticles,and sunken stomata. Many desert plants use the $CAM$ pathway,which allows stomata to remain closed during the day,significantly reducing water loss through transpiration.
$(c)$ Behavioural adaptations in animals: Organisms exhibit behavioural changes like hibernation,aestivation,and migration to escape environmental stress. Ectotherms (cold-blooded animals) like lizards bask in the sun to warm up and burrow into the sand to cool down. Endotherms (warm-blooded animals) may hibernate or aestivate to survive extreme temperatures.
$(d)$ Importance of light to plants: Sunlight is the primary energy source for photosynthesis. Light also regulates photoperiodic responses,which are essential for flowering in many plants. In aquatic habitats,light intensity determines the vertical distribution of plants.
$(e)$ Effect of temperature or water scarcity and the adaptations of animals: Temperature affects animal distribution; eurythermal animals tolerate a wide range of temperatures,while stenothermal animals tolerate a narrow range. Animals in cold regions have shorter ears and limbs to prevent heat loss,and thick fat layers (blubber) for insulation. Water scarcity leads to physiological adaptations like concentrated urine in kangaroo rats and behavioural adaptations like burrowing in desert reptiles.