The tropical rainforest biome is one of the most diverse and productive biomes on Earth. Tropical rainforests provide 40 per cent of the oxygen on Earth even though they only cover about 6 per cent of the Earth's surface. The biome is characterised by its rainfall and evergreen species. Approximately 25 per cent of the medications in use today have come from tropical rainforests. The three largest tropical rainforests lie in South America, Africa and Asia.
Geographically speaking, tropical rainforests occur near the equator. This is the only area on Earth where temperatures are warm enough year round to support the plant life of the rainforest. Even though they all share a proximity to the equator, each of the three largest forests has unique species of plants and animals.
All rainforests are characterised by a unique layer system consisting of the emergent, upper canopy, understory and forest floor. Trees that make up the emergent layer are typically 100 to 240 feet tall and their leaves form a canopy over the forest floor. The upper canopy layer consists of shorter trees that soak up much of the sunlight allowed in by the emergent trees. Below the upper canopy, sunlight is in short supply. The understory is composed of even shorter trees, along with shrubs and plants. Due to the two layers above it, the understory receives constant shade. The forest floor is not very lush as the soil is thin and lacks quality, and less than 1 per cent of sunlight is able to penetrate this far. Some plant species and herbs grow here.
Tropical rainforests are defined by their year-round warm temperatures and rainfall levels. Temperatures typically fall within the 20 to 33.9 degrees Celsius range and rainfall often exceeds 100 inches a year. Humidity in rainforests ranges from 77 to 88 per cent. Most tropical rainforests experience a period of time that is dryer than the rest of the year, but only a few experience a true dry season.
The tropical rainforest is the most diverse biome in terms of plant life. This is the reason scientists have isolated so many beneficial compounds used in medicines. The plants and trees in the rainforest have developed several adaptations to deal with the excessive water and lack of sunlight. These adaptations include large, wide leaves that move to soak up the most sun to "drip tips" on many leaves that channel water to the roots of the plant. Many plants live high up on tree trunks to get the sunlight they need to survive.
The animal species vary from rainforest to rainforest, but all contain several species of monkeys, along with other mammals, birds, reptiles and amphibians. Many species have adapted to survive in trees, including the jaguars in the Central and South American rainforests. The herbivore diet is mainly fruits, since they are abundant in the rainforest. The most abundant animals in all rainforests are insects, including ants, mosquitoes and butterflies.