Science Natural Science What You Need to Know About Biomes How All of Living Organisms in the World Live With One Another By Jenn Savedge Jenn Savedge Writer University of Strathclyde Ithaca College Jenn Savedge is an environmental author and lecturer. She’s a former national park ranger who has written three books on eco-friendly living Learn about our editorial process Updated March 14, 2018 Share Twitter Pinterest Email Posnov / Getty Images Science Space Natural Science Technology Agriculture Energy If you want to learn about ecology, the first thing you need to understand is how all of living organisms in the world live with one another. A biome is an ecosystem or group of ecosystems that can be characterized by its vegetation, plant and animals life, climate, geology, elevation, and rainfall. Biomes are large ecosystem units. So while a puddle may be considered an ecosystem, the Pacific Ocean would be considered a biome. In most cases, the plants and animals in a biome will have special adaptations that make living in that community most successful. So when ecologists study a particular plant or animal, they generally study its entire biome to have a better understanding of the role that species plays in its community. There are five basic types of land biomes and two categories of aquatic biomes. Each biome can then be broken down into a number of sub-biomes or zones that all have their own unique set of geographic characteristics. Here are the defining characteristics of the world's biomes: Land Biomes Tundra: A tundra is a treeless biome that is characterized by long, cold winters and short tepid summers. The word tundra comes from the Russian word for "uplands." The cooler temperatures and shorter growing season limits the types of plants that are found in tundras to grasses, mosses, lichen, low shrubs, and a few flowering plants. The three main types of tundra are the arctic tundra, alpine tundra, and Antarctic tundra. Grassland: As the name suggests, grasslands are characterized by the predominance of grasses and grass-like plants, such as sedge and rush. Savannas are a type of grassland that also include a few scattered trees. Grasslands can be found on every continent in the world except for Antarctica. Forest: In the forest biome, large groups of trees live together in close relationship with each other and with the other living things in the environment. In general, the trees in a forest are so abundant that their tops touch or overlap, shading the ground. Tropical rainforest, boreal forest, and temperate forest are a few types of forest biome. Desert: Rainfall - or the lack of it- is the defining characteristic of the desert biome. Deserts get less than 10 inches of rainfall per year. Because of this, many deserts have little to no vegetation while others have a few scattered low shrubs or grasses. Deserts are usually classified as hot or cold or semi-arid or coastal. Mountain: Every continent on Earth has a mountain biome. Mountains are land masses that are usually found in groups called chains or ranges although some do exist on their own. A single mountain may have many ecosystems within it, starting with a desert at the base, changing to a forest as the elevation rises, and topped off with a tundra. Aquatic Biomes Water biomes make up over 75 percent of the Earth's surface. They consist of freshwater ecosystems such as ponds and lakes, streams and rivers, and wetlands, as well as marine regions such as coral reefs, oceans, and estuaries.Marine biomes are distinguished from freshwater by the presence dissolved compounds - usually salts - in the water. The amount of salt - or salinity - varies within each of the marine ecosystems. Biomes play a critical role in the understanding of ecology because they help scientists study not only a specific plant or animal but also the role it plays in its community and the characteristics that it has developed to live in its environment.