Deserts, tundra and water biomes

Deserts are the driest biomes: they get very little rain. Some are hot (the Sahara, in Africa); some are cold (the Gobi, in Asia). India has a special one: the Rann of Kutch in Gujarat, one of the world's largest salt deserts. In the monsoon it becomes a marshy wetland; in the dry season it turns into a vast white salt desert.

Life in a desert is hard, so living things have adapted (changed over a long time to suit the place):

• Cacti store water in their thick stems, and their leaves are spines, which lose less water.
• Camels, lizards and snakes can store water or go long without it, and can stand heat and dryness.

Compare two camels (Fig. 2.7). The Rajasthan camel of the hot Thar has one hump and short, thin hair: it needs to stay cool. The Nubra Valley camel of Ladakh, a cold desert, has two humps and thick, shaggy fur: it needs to stay warm. Same animal family, different coats, because the climates differ. (The hump stores fat, not water.)

Deserts often have sandy soil and few plants, but they have their own special ecosystems, and many give minerals and oil.

Tundra is the coldest biome, near the Arctic and Antarctic regions. Winters are very long and harsh, summers short. The ground stays frozen almost all year: this is permafrost. Trees cannot push their roots into frozen ground, so only mosses, lichens and small shrubs grow. Reindeer, polar bears and arctic foxes are built for the freezing cold. The tundra is fragile: even a small change in temperature can upset it.

Compare the Himalaya: it is high and cold too, but it lies in the subtropics, so it gets more warmth and a longer growing season, and its slopes are covered with conifers.

Water biomes (aquatic biomes) take up about three-fourths of the Earth's whole surface.

• Freshwater: rivers, lakes, ponds and wetlands. They give water for drinking and farming, and are home to fish, frogs and insects.
• Marine: oceans, seas and coral reefs. They are rich in life (whales, dolphins, fish, tiny drifting plankton), feed millions of people, and store and spread heat, which shapes the Earth's climate.