This document describes the major terrestrial and aquatic ecosystems. There are six primary terrestrial ecosystems: tundra, taiga, temperate deciduous forest, tropical rainforest, grassland, and desert. Aquatic ecosystems include marine ecosystems, which cover most of the Earth's surface, and freshwater ecosystems, which include lakes, rivers, and streams. Each ecosystem has distinctive characteristics and adaptations that allow organisms to thrive in their particular environment.