The biosphere is divided into regions called biomes that exhibit common environmental characteristics.

Each biome is occupied by unique communities or ecosystems of plants and animals that share adaptations which promote survival within the biome. Following is a list of the major biomes and a summary of their characteristics:

1. Tropical rain forests are characterized by high temperature and heavy rainfall. The vegetation consists predominately of tall trees that branch only at their tops, forming a spreading canopy that allows little light to reach the forest floor. Epiphytes (plants that live commensally on other plants) and vines commonly grow on the trees, but due to lack of light, little grows on the forest floor.

2. Savannas are grasslands with scattered trees. Because savannas are tropical, they are subject to high temperatures. However, they receive considerably less water than rain forests.

3. Temperate grasslands receive less water and are subject to lower temperatures than are savannas. The North American prairie is an example.

4. Temperate deciduous forests occupy regions that have warm summers, cold winters, and moderate precipitation. Deciduous trees shed their leaves during the winter, an adaptation to poor growing conditions (short days and cold temperatures).

5. Deserts are hot and dry. Growth of annual plants is limited to short periods following rains. Other plants have adapted to the hostile conditions with leathery leaves, deciduous leaves, or leaves reduced to spines (cacti). Many animals have thick skins, conserve water by producing no urine or very concentrated urine, and restrict their activity to nights.

6. Taigas are characterized by coniferous forests (pines, firs, and other trees with needles for leaves). Winters are cold, and precipitation is in the form of snow.

7. Tundras are subject to winters so cold that the ground freezes. During the summer, the upper topsoil thaws, but the deeper soil, the permafrost, remains permanently frozen. During the summer, the melted topsoil supports a grassland type community consisting of grasses, sedges, and other vegetation tolerant of soggy soils.

8. Fresh water biomes include ponds, lakes, streams, and rivers.

9. Marine biomes include estuaries (where oceans meet rivers), intertidal zones (where oceans meet land), continental shelves (the relatively shallow oceans that border continents), coral reefs (masses of corals that reach the ocean surface), and the pelagic ocean (the deep oceans).