Science · Grades 3–6

Rainforest

Reading comprehension lesson about rainforests — the most biodiverse ecosystems on Earth, home to half of all known species.

Reading Passage

Rainforest

Rainforests are dense forests that receive more than 80 inches of rainfall per year. They are found near the equator in South America, central Africa, and Southeast Asia, where warm temperatures and abundant rain create ideal conditions for plant growth. Although tropical rainforests cover only about 6 percent of Earth’s land surface, they are home to more than half of all known plant and animal species. The Amazon rainforest in South America is the largest, covering about 2.7 million square miles.

Rainforests are organized into distinct vertical layers. The emergent layer consists of the tallest trees, which poke above the main canopy and are exposed to direct sunlight and strong winds. Below it is the canopy, a dense ceiling of overlapping branches and leaves 60 to 100 feet off the ground where most rainforest animals live. The understory is a dim layer of shorter trees, shrubs, and climbing plants. The forest floor receives almost no direct sunlight and is covered with decomposing leaves that are rapidly broken down by fungi and insects.

The biodiversity of rainforests is staggering. A single hectare (about 2.5 acres) of Amazon rainforest may contain 400 or more tree species and thousands of insect species. Many rainforest species have not yet been described by scientists. Rainforests are a major source of medicines — about 25 percent of modern pharmaceuticals are derived from rainforest plants, and indigenous peoples have used thousands of plant species medicinally for centuries. Many potential cures for diseases may still be waiting to be discovered.

Rainforests play a vital role in regulating Earth’s climate. They absorb enormous amounts of carbon dioxide and release oxygen, earning them the nickname “the lungs of the Earth.” They also cycle vast quantities of water through evapotranspiration, influencing rainfall patterns far beyond their borders. Despite their importance, rainforests are being destroyed at an alarming rate through logging, farming, and ranching. Scientists estimate that an area the size of a football field is cleared every single second.

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