Arid Land/Deserts – SS1 Biology Lesson Note (Third Term)

Arid lands, or deserts, are areas of very low rainfall and high evaporation rates. They are the driest habitats and receive less than 25 cm of rainfall a year. Deserts are hot or cold, have scanty vegetation and sandy or rocky soils, and contain plants and animals adapted to survive with very little water.

Behavioural objectives

By the end of the lesson, students should be able to:

• define arid lands and name the two types, with examples
• state the characteristics of a desert
• describe how desert plants are adapted to their habitat
• describe how desert animals are adapted to their habitat
• write food chains found in arid lands

What are arid lands (deserts)?

Arid lands are areas of very low rainfall and high evaporation rates. They are the driest habitats, receiving less than 25 cm of annual rainfall.

Types of arid land

• Hot deserts: for example the Sahara Desert (North Africa) and the Kalahari Desert (South Africa).
• Cold deserts: for example the deserts in North America.

What are the characteristics of a desert?

1. Water is very scarce.
2. Temperature is very high during the day and very low at night.
3. Vegetation is very scanty.
4. The soils are sandy or rocky.
5. Strong winds occur frequently and sunshine is very intense.
6. Drought-resistant plants (xerophytes) are present.

How are plants distributed and adapted in deserts?

Desert plants include thorny bushes, cacti, scattered dwarf acacia, date palms, wiry grasses, baobab trees and euphorbia species. They adapt to this habitat in the following ways:

1. Plants have small leaves to reduce transpiration.
2. Cacti have thorns instead of leaves to reduce transpiration, and thick succulent stems to store water.
3. Acacia (drought resistant) has deep roots which absorb underground water.
4. The baobab tree has waxy leaves, which can be hairy or needle-shaped, to reduce the rate of transpiration.
5. Wiry grass has narrow and slender leaves to reduce transpiration.

How are animals distributed and adapted in deserts?

Desert animals include the camel, rodents, lizards, snakes, zebras, desert tortoises, grasshoppers, wasps and ants. They survive in the following ways:

1. Most desert animals excrete solid wastes to conserve water.
2. Kangaroos and rats remain in burrows during the day to avoid excessive heat.
3. Reptiles have scales to reduce water loss.
4. Camels can survive several days without drinking water. They can withstand a wide range of body temperature, up to 40 °C.
5. Locusts have water-proof bodies and impervious cuticles.

What food chains are found in arid lands?

1. Plants → desert rats → snakes
2. Plants → ants → scorpions → snakes

Evaluation

1. What are arid lands? Name the two types and give one example of each.
2. State four characteristics of a desert.
3. Explain two ways in which desert plants reduce water loss.
4. Describe two ways in which desert animals survive with little water.
5. Write one food chain found in arid lands.

Assignment

1. Describe how the cactus and the acacia are adapted to desert life.
2. List four desert animals and state one adaptation of any two of them.