Life Science · Grades 6–8

Biomes

Deserts, rainforests, tundra, coral reefs, and more.

Travel from the Arctic toward the equator and the land keeps changing: frozen tundra, dark conifer forests, leafy woods, grassy plains, and hot deserts. Each of these is a biome, and the climate decides which one you are in.

On this page you will learn what makes a biome, meet the eight major land biomes, and dive into the water biomes that cover most of our planet. Then try Which Biome? and the six-question quiz.

Play Which Biome? Take the quiz

What is a biome?

A biome is a large area of Earth with a similar climate and similar kinds of plants and animals. Biomes are bigger than the ecosystems you met on the Ecosystem Interactions page. One biome, such as the desert, can show up on several continents, far apart, wherever the climate is alike.

Scientists sort biomes into two big groups. Land biomes are named mostly for their main plants, such as grasses, shrubs, or kinds of trees. Water biomes are sorted by how salty the water is, how deep it is, and whether it moves.

Climate decides

On land, two parts of climate matter most: temperature and precipitation, which is rain and snow. Together they decide how long plants can grow each year and how much water they get. Plants, in turn, decide which animals can live there.

The chart shows how much precipitation falls each year in six land biomes. A tropical rainforest can get more than 20 times as much as a desert.

Yearly rain and snow in six land biomes, in centimeters. Data: OpenStax Biology 2e, section 44.3. Ranges overlap, so temperature matters too: a temperate grassland and a boreal forest can get similar amounts.

The eight land biomes

Biologists usually describe eight major land biomes. Here they are, from the warm, wet tropics to the frozen north.

Tropical rainforest

Found near the equator. Temperatures stay between about 20 and 34 °C, and 125 to 660 cm of rain falls a year. It has more kinds of trees than any other biome: 100 to 300 species can grow in one hectare of the Amazon. The forest grows in layers, from the forest floor up through the understory and canopy to the tallest emergent trees, and plants called epiphytes grow on other plants.

Savanna

Grassland with scattered trees, found in Africa, South America, and northern Australia. It is hot, from about 24 to 29 °C, with a long dry season. Fires are common, and many plants survive by growing back from their roots.

Desert

Subtropical deserts lie between about 15° and 30° north and south of the equator. They get less than 30 cm of rain a year, some as little as 2 cm. By day the soil can heat above 60 °C, and at night it can cool to near 0 °C. Some plants, like the ocotillo, grow leaves only after it rains.

Chaparral

Found in California, around the Mediterranean Sea, and in southern Australia. It gets 65 to 75 cm of rain a year, mostly in winter, and summers are dry. Shrubs are the main plants, and some seeds sprout only after a fire.

Temperate grassland

Called prairies in North America and steppes in Eurasia. It gets 25 to 75 cm of precipitation a year and has hot summers and cold winters. Grass roots pack the soil, making it deep and fertile. Fires, mostly started by lightning, keep trees from taking over, and grazers like the American bison once roamed in huge numbers.

Temperate forest

Temperatures range from about −30 to 30 °C, with 75 to 150 cm of precipitation a year. Most trees are deciduous: they drop their leaves each fall and grow new ones in spring. The fallen leaf litter breaks down and adds nutrients to the soil.

Boreal forest

Also called the taiga, it stretches across Canada, Alaska, Russia, and northern Europe. Winters are long and cold, and the 40 to 100 cm of yearly precipitation falls mostly as snow. Evergreen conifers, such as pines, spruces, and firs, keep their needles all year.

Tundra

The Arctic tundra is the coldest land biome. Winters average about −34 °C, and summers are only 3 to 12 °C. Plants can grow for only 10 to 12 weeks a year. Below the surface lies permafrost, ground that stays frozen all year, so only low plants such as shrub willows, and lichens, can grow.

Water biomes

The ocean covers more than 70% of Earth’s surface and holds about 97% of its water. Only about 2.5% of Earth’s water is fresh, and most of that is frozen in ice or stored underground.

The ocean

Ocean life depends on light. In the photic zone, the top 200 m or so, there is enough sunlight for algae and plankton to carry out photosynthesis. Below that is the dark aphotic zone. The ocean averages about 3,682 m deep, and the abyssal zone starts at about 4,000 m. There, near hot vents on the sea floor, bacteria make food from chemicals instead of sunlight.

The ocean from top to bottom, not to scale. The deepest known point, the Challenger Deep, is about 10,935 m down. Data: OpenStax Biology 2e, section 44.4, and NOAA Ocean Service.

Coral reefs

Coral reefs grow in warm, shallow, sunlit water. They cover less than 1% of the ocean floor, yet about 25% of marine species depend on them. More than 4,000 kinds of fish live on coral reefs.

Estuaries

An estuary forms where a river meets the sea, so fresh water and salt water mix. As the tides come in and go out, the saltiness changes quickly. Many plants there are halophytes, which can handle salty conditions.

Fresh water

Freshwater biomes include lakes and ponds, where water stands still, and rivers and streams, where it flows. Wetlands are freshwater biomes too. In summer the sun warms a lake’s top layer, which does not mix with the colder water below.

Key words

Biomea large area with a similar climate and similar kinds of plants and animals
Climatethe usual weather of a place over many years
Precipitationwater that falls from the sky as rain, snow, sleet, or hail
Deciduousdropping all leaves each year, usually in fall
Conifera tree with cones and, usually, needle-shaped leaves that stay green all year
Permafrostground that stays frozen all year
Photic zonethe top layer of water, where there is enough sunlight for photosynthesis
Estuarya place where a river meets the sea and fresh and salt water mix

Game: Which Biome?

You will see twelve clues, one at a time. Pick the biome each clue describes from three choices. A clue you match on your first try earns 1 point, for a total of 12. Your best score is saved on this device.

The game needs JavaScript. You can still check every clue in the table below.

Work through it without the game. Cover the two right-hand columns, name the biome for each clue, then check.

Which Biome?: all twelve clues
Clue	Biome	Why
Warm all year, 125 to 660 cm of rain, and up to 300 kinds of trees in one hectare	Tropical rainforest	Tropical rainforests stay between about 20 and 34 °C and have more kinds of trees than any other biome: 100 to 300 species in one hectare of the Amazon.
Grass with scattered trees, a long dry season, and plants that resprout after fires	Savanna	Savannas are hot grasslands in Africa, South America, and northern Australia. Fire is common, and many plants grow back from their roots.
Less than 30 cm of rain a year and soil above 60 °C by day	Desert	Subtropical deserts get under 30 cm of rain a year, sometimes as little as 2 cm. Nights can cool to near 0 °C.
Dense shrubs, rain mostly in winter, and seeds that sprout only after a fire	Chaparral	Chaparral grows in California, around the Mediterranean, and in southern Australia, with 65 to 75 cm of rain a year.
Called prairie in North America and steppe in Eurasia, with deep, rich soil	Temperate grassland	Temperate grasslands get 25 to 75 cm of rain a year. Fires, mostly started by lightning, keep trees from taking over.
Trees drop their leaves in fall, and the fallen leaves enrich the soil	Temperate forest	Most temperate forest trees are deciduous. The leaf litter breaks down into nutrients, and rain is 75 to 150 cm a year.
Long, cold winters, much of the water falling as snow, and evergreen conifers	Boreal forest	The boreal forest, or taiga, stretches across Canada, Alaska, Russia, and northern Europe. It gets 40 to 100 cm of precipitation, mostly as snow.
Frozen ground called permafrost and a growing season of only 10 to 12 weeks	Tundra	In the Arctic tundra, winters average about −34 °C. Low plants such as shrub willows, and lichens, grow over the permafrost.
Less than 1% of the ocean floor, but home to about a quarter of marine species	Coral reef	Coral reefs are built by tiny animals in warm, shallow water. More than 4,000 kinds of fish live on them.
Where a river meets the sea, and the saltiness changes with the tides	Estuary	In an estuary, fresh and salt water mix. Plants and animals there must handle saltiness that keeps changing.
Cold and dark, 4,000 m and deeper, where bacteria at hot vents make food from chemicals.	Deep ocean	The abyssal zone is cold and dark. Near hydrothermal vents, bacteria use chemicals instead of sunlight to make food.
Standing fresh water whose sun-warmed top layer does not mix with the cold water below in summer	Lake or pond	Lakes and ponds hold standing fresh water. In summer the sun warms the top layer, and light reaches only the upper, photic zone.

Quick quiz

Six questions. Pick one answer for each, then press Check my answers.

1. What two things mostly decide which land biome a place has? Soil color and wind Temperature and precipitation How many animals live there and how big they grow

2. Which biome has long, cold winters and evergreen conifers? Boreal forest Temperate grassland Tropical rainforest with tall broad-leaved trees

3. Why are trees rare on temperate grasslands? The soil is too poor Bison eat every tree Too little rain, and fires that burn back young trees

4. About how deep does enough sunlight for photosynthesis reach in the ocean? About 20 m About 200 m All the way to the bottom, about 3,682 m on average

5. What makes an estuary a hard place to live? It is always frozen The saltiness keeps changing with the tides There is no light at all, so nothing there can make food

6. Which statement about coral reefs is true? About 25% of marine species use them They grow mostly in cold, dark water They cover about half of the ocean floor

Answer key: 1. Temperature and precipitation. 2. Boreal forest. 3. Too little rain, and fires that burn back young trees. 4. About 200 m. 5. The saltiness keeps changing with the tides. 6. About 25% of marine species use them.

Talk about it

Which biome do you live in? What clues about its climate and plants tell you?
Deserts are found on several continents far apart. Why would the same biome appear in such distant places?
Without fires, a temperate grassland can turn into scrub or forest. Should people ever start fires on purpose to protect a grassland?
Coral reefs cover a tiny part of the ocean floor but hold a huge share of its species. Why might a small place matter so much?
If a place became warmer and drier over many years, how might its biome change?

Sources and credits

OpenStax, Biology 2e, 44.3 Terrestrial Biomes (eight major land biomes; temperatures, precipitation, plants, and locations for each).
OpenStax, Biology 2e, 44.4 Aquatic Biomes (photic zone to about 200 m; abyssal zone from about 4,000 m; hydrothermal vents; more than 4,000 fish species on coral reefs; estuaries and halophytes; lakes, ponds, rivers, and wetlands).
NOAA Ocean Service, How much water is in the ocean? (more than 70% of Earth’s surface; about 97% of its water).
NOAA Ocean Service, How deep is the ocean? (average depth about 3,682 m; Challenger Deep about 10,935 m).
NOAA Fisheries, Corals (reefs cover less than 1% of the ocean floor and support about 25% of marine species).
U.S. Geological Survey, Where is Earth’s Water? (about 2.5% of Earth’s water is fresh; most of it in ice and groundwater).
NASA Science, New Land Cover Classification Maps (MODIS on Terra; Boston University; images from November 2000 to October 2001; 1 km detail), and NASA Earthdata, MODIS Land Cover Type, yearly.

Credits

Text, game, and quiz written by Dian, Life Science teacher at Jugami. All diagrams are original, hand-coded SVG drawings made for this page, and the share image was drawn in code. The rain chart uses the numbers from the sources above; other diagrams are simplified and not to scale.