Biomes at Higher Level: The same statement as SL. HL questions ask what a biome is, the climate of a named biome, and how convergent evolution makes communities on different continents alike.
Practise this as you read
- State what a biome is.
- Identify the climate conditions of a named biome.
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The big idea: A biome is a large region of the Earth that has a particular climate and a characteristic community of plants and animals.
Biomes you should know
- Hot desert
- Tropical rainforest
- Temperate forest
- Grassland
- Taiga
- Tundra
What decides the biome: What decides which biome forms in a place is mostly two abiotic (non-living) factors: temperature and precipitation (rainfall). Together these set the conditions that plants — and the animals that depend on them — must live in.
- Biome
- A large geographical region with a particular climate and a characteristic community of organisms (for example tropical rainforest or tundra).
- Climate
- The typical pattern of temperature and precipitation in a region, averaged over many years.
- Abiotic factor
- A non-living physical or chemical feature of the environment, such as temperature, rainfall, light or soil.
- Precipitation
- Water that falls onto the land, mainly as rain (also snow). It determines how much water is available to organisms.
- Temperature
- How hot or cold a region is. It affects which organisms can survive and how fast biological processes happen.
Why temperature and rainfall matter most: Plants are the base of almost every community, and plants are limited above all by how warm it is and how much water there is.
So if you know a region's temperature and its precipitation, you can predict which biome — and therefore which kind of vegetation — it will have.
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The big idea: Each biome has its own pattern of temperature and rainfall, and that climate decides its typical vegetation.
The points to remember
- Tropical forest: hot and wet all year; tall evergreen trees; nutrient-poor soil; very high biodiversity.
- Temperate forest: mild with four seasons and rain all year; broadleaf trees that drop their leaves.
- Taiga: long, cold winters; moderate precipitation, much as snow; conifers.
- Grassland: hot summers, cold winters and a dry season; grasses with few trees.
- Tundra: very cold and dry, with frozen ground; mosses, lichens and low shrubs.
- Hot desert: very little rain, hot days and cool nights; sparse cacti and shrubs.
Remember it as: Name the biome, then its temperature, its rainfall and its plants.
Questions often give two or three clues, such as climate, soil and biodiversity, and ask for the biome: match every clue, not just one.
Trap: Tundra and hot desert both get under 25 cm of rain a year: only the temperature tells them apart.
The big idea: A biome is a group of ecosystems with similar communities. They look alike because similar abiotic conditions select similar adaptations: convergent evolution.
The points to remember
- Convergent evolution: unrelated species evolve similar features because they live in similar conditions.
- Ecosystems of one biome can be on different continents, with different species.
- Their communities are still similar in structure: the same kinds of plants and the same adaptations.
Remember it as: Same conditions, same solutions, different ancestors.
Real example: two gliders. Sugar gliders in Australian forests and southern flying squirrels in North American forests both glide between trees on flaps of skin, yet one is a marsupial and the other a rodent: convergent evolution.
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How it is asked: Expect 'state what a biome is', a choice of climate conditions for a named biome, or a biome to name from its climate, soil and biodiversity.
Explain why the tropical rainforests of South America and South-East Asia are classed as the same biome, although they share few species.
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