(a) Adaptations of desert plants and animals

 $\to$Adaptations of desert plants

Plants found in deserts are well adapted to cope with harsh desert conditions such

as water scarcity and scorching heat. Plants have an extensive root system to tap

underground water. They bear thick cuticles and sunken stomata on the surface

of their leaves to reduce transpiration. In Opuntia, the leaves are entirely modified 

into spines and photosynthesis is carried out by green stems. Desert plants have

special pathways to synthesize food, called CAM (C4 pathway). It enables the

stomata to remain closed during the day to reduce the loss of water through

transpiration.

$\to$ Adaptations of desert animals

Animals found in deserts such as desert kangaroo rats, lizards, snakes, etc. are

well adapted to their habitat. The kangaroo rat found in the deserts of Arizona

never drinks water in its life. It has the ability to concentrate its urine to conserve

water. Desert lizards and snakes bask in the sun during early morning and burrow

themselves in the sand during afternoons to escape the heat of the day. These

adaptations occur in desert animals to prevent the loss of water.

(b) Adaptations of plants to water scarcity

Plants found in deserts are well adapted to cope with water scarcity and scorching

heat of the desert. Plants have an extensive root system to tap underground water.

They bear thick cuticles and sunken stomata on the surface of their leaves to

reduce transpiration. In Opuntia, the leaves are modified into spines and the

process of photosynthesis is carried out by green stems. Desert plants have special

pathways to synthesize food, called CAM (C4 pathway). It enables their stomata

to remain closed during the day to reduce water loss by transpiration.

(c) Behavioural adaptations in animals

Certain organisms are affected by temperature variations. These organisms

undergo adaptations such as hibernation, aestivation, migration, etc. to escape

environmental stress to suit their natural habitat. These adaptations in the

behaviour of an organism are called behavioural adaptations. For example,

ectothermal animals and certain endotherms exhibit behavioral adaptations.

Ectotherms are cold blooded animals such as fish, amphibians, reptiles, etc. Their

temperature varies with their surroundings. For example, the desert lizard basks

in the sun during early hours when the temperature is quite low. However, as the

temperature begins to rise, the lizard burrows itself inside the sand to escape the

scorching sun. Similar burrowing strategies are exhibited by other desert animals.

Certain endotherms (warm-blooded animals) such as birds and mammals escape

cold and hot weather conditions by hibernating during winters and aestivating

during summers. They hide themselves in shelters such as caves, burrows, etc. to

protect against temperature variations.

(d) Importance of light to plants

Sunlight acts as the ultimate source of energy for plants. Plants are autotrophic

organisms, which need light for carrying out the process of photosynthesis. Light

also plays an important role in generating photoperiodic responses occurring in

plants. Plants respond to changes in intensity of light during various seasons to

meet their photoperiodic requirements for flowering. Light also plays an

important role in aquatic habitats for vertical distribution of plants in the sea.

(e) Effects of temperature or water scarcity and the adaptations of animals.

Temperature is the most important ecological factor. Average temperature on the

Earth varies from one place to another. These variations in temperature affect the

distribution of animals on the Earth. Animals that can tolerate a wide range of

temperature are called eurythermals. Those which can tolerate a narrow range of

temperature are called stenothermal animals. Animals also undergo adaptations

to suit their natural habitats. For example, animals found in colder areas have

shorter ears and limbs that prevent the loss of heat from their body. Also, animals

found in Polar regions have thick layers of fat below their skin and thick coats of

fur to prevent the loss of heat.

Some organisms exhibit various behavioural changes to suit their natural habitat.

These adaptations present in the behaviour of an organism to escape

environmental stresses are called behavioural adaptations. For example, desert

lizards are ectotherms. This means that they do not have a temperature regulatory

mechanism to escape temperature variations. These lizards bask in the sun during

early hours when the temperature is quite low. As the temperature begins to

increase, the lizard burrows itself inside the sand to escape the scorching sun.

Similar burrowing strategy is seen in other desert animals.

Water scarcity is another factor that forces animals to undergo certain adaptations

to suit their natural habitat. Animals found in deserts such as desert kangaroo rats,

lizards, snakes, etc. are well adapted to stay in their habitat. The kangaroo rat

found in the deserts of Arizona never drinks water in its life. It has the ability to

concentrate its urine to conserve water. Desert lizards and snakes bask in the sun

during early morning and burrow in the sand as the temperature rises to escape

the heat of the day. Such adaptations can be seen to prevent the loss of water.