Desert Biome — Reading Comprehension Lesson

Reading Passage

Desert Biome

Deserts are defined not by heat but by dryness: a desert is any area that receives less than 10 inches of precipitation per year. Deserts cover about one-third of Earth’s land surface, making them the most widespread land biome. The Sahara in North Africa is the world’s largest hot desert, covering about 3.5 million square miles. However, not all deserts are hot — the Antarctic and Arctic are classified as polar deserts because they receive very little precipitation, and the Gobi Desert in Asia experiences bitter cold winters.

Desert plants have evolved remarkable adaptations to conserve water. Cacti store water in their thick, fleshy stems and are covered with a waxy coating to reduce evaporation. Their leaves have been reduced to spines, which also protect against herbivores. Many desert plants have very deep taproots that reach underground water sources, or wide shallow root systems that quickly absorb rain before it evaporates. Some desert plants, called ephemerals, spend most of their lives as dormant seeds and bloom explosively after rare rains.

Desert animals face the challenge of surviving extreme heat and water scarcity. Many are nocturnal, sheltering underground or in rock crevices during the scorching day and becoming active at night when temperatures drop. The fennec fox of the Sahara has enormous ears that radiate heat, keeping it cool. Kangaroo rats and some other desert rodents never need to drink water at all — they extract water from the dry seeds they eat through metabolic processes. Reptiles are particularly well-suited to deserts because their scaly skin prevents water loss.

Despite their harsh conditions, deserts are not lifeless. They support surprisingly diverse communities of plants, animals, insects, and microorganisms, all adapted to the extremes of their environment. Desert soils develop a biological crust — a living community of cyanobacteria, mosses, and fungi — that holds soil in place and captures moisture. This crust is extremely fragile and can be destroyed by a single footstep, making it vulnerable to human disturbance.

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