Relationship between climate & biomes (WJEC Eduqas GCSE Geography B): Revision Note

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The notes on this page cover part 3.1.1 of the WJEC Eduqas GCSE B Geography.

3.1.1 - What is the relationship between climate and biomes at a global scale?

• The location and distribution of biomes at a global scale and their relationship to climate zones

The location and distribution of global biomes

• There are 11 biomes in Earth's biosphere

• A biome is a group of ecosystems around the world with similar climate and vegetation characteristics

Biome distribution

• The factors which affect biome distribution include:

  • Latitude: with distance from the equator, temperatures and sunshine hours decrease 

  • Precipitation: overall areas of high pressure experience low rainfall, and areas of low pressure experience high rainfall

  • Altitude: an increase in altitude leads to a decrease in temperature

  • Continentality: locations further inland heat up more quickly in the summer and cool more quickly in the winter

  • Ocean currents: warm and cold currents circulate in the oceans, either warming or cooling the adjacent land 

• Climate is the most significant factor affecting biome distribution

  • The global biomes match the distribution of climates

What is an ecosystem?

• An Ecosystem is a community of living organisms (plants and animals) and their non-living environment

• They function most efficiently when they are in balance:

  • The living (biotic) and non-living components (abiotic) are linked and interact with each other to try to maintain this balance

• Ecosystems vary in size and scale 

  • A small ecosystem could be a garden pond

  • A large-scale ecosystem could be all tropical rainforests – this is a biome

• All ecosystems have inputs, stores, transfers and outputs

  • Inputs: solar radiation and precipitation

  • Stores: biomass and soil

  • Transfers: energy is transferred through food chains and webs

  • Outputs: gases, dead matter

Interdependence in ecosystems

• Within an ecosystem, the different biotic components depend on each other, and the abiotic components for survival (food, water and shelter)

• This is known as interdependence

  • It means that changes in one component can have significant impacts on other parts of the ecosystem

• One of the main interactions between biotic components is feeding

  • These interactions can be shown as food chains and food webs

Food chains and webs

• Within all food chains and food webs, there are examples of:

  • Producers: Food chains always start with a producer

  • Primary consumers: Producers are eaten by primary consumers (herbivores/omnivores)

  • Secondary consumer: Primary consumers are eaten by secondary consumers (carnivores/omnivores)

  • Tertiary consumer: Secondary consumers are eaten by tertiary consumers (carnivores/omnivores)

• There are also decomposers.

• These are fungi and bacteria, and they:

  • Help to return energy/nutrients back to the soil

  • Break down dead organic matter, plant/animal waste

  • Release energy from organic matter so it can be recycled

Food chains 

• A food chain shows the feeding interactions and transfer of energy from one organism to the next

• As each plant or animal is eaten, energy is passed on to the consumer

• The source of energy in a food chain is light energy from the sun

Food webs

• The links between the biotic components can also be shown as a food web

• These show the complex variety of plants and animals which feed on each other

• For example, in the food web above, if the population of mice decreased:

  • The population of grass plants would increase, as there are now fewer species feeding on them

  • The populations of sparrow hawks would decrease, as mice are a main part of their food

  • The population of small birds may decrease as more of these are eaten by the sparrow hawks due to the lack of mice

Water, nutrient and carbon cycles in ecosystems

How do ecosystems regulate water supply?

• Every ecosystem forms part of the water cycle

• This means that it has stores and flows (transfers) of water

• Ecosystems store fresh water in:

  • Ice/snow

  • Rivers, streams and lakes

  • Plants

  • Soil

• Water is transferred through ecosystems by:

  • Stemflow – which is water running down branches and trunks

  • Drip flow - water running off leaves

  • Evaporation from water stores

  • Transpiration from the leaves of plants

• The amount of water stored and transferred depends on the type of ecosystem

• In a tropical rainforest, the trees and plants intercept much of the precipitation

  • It is then returned to the atmosphere via evaporation off the leaves and branches, or runs slowly to the ground through drip flow and stem flow

• The water then gradually reaches the streams and rivers

• When areas of forest are cleared, this cycle is broken

  • More precipitation reaches the soil surface, leading to soil erosion and flooding

  • Less water is intercepted or taken up by the trees and plants, so rates of transpiration and evaporation decrease

• This leads to lower rates of precipitation due to less water in the atmosphere

Nutrient cycles

• Nutrients and minerals are essential for plant growth

• These can be found in rocks, the atmosphere and water

  • Soil (abiotic) is formed from minerals and particles from weathered rock (abiotic), dead plants, and animals (biotic)

  • Soil, water and solar energy (abiotic) then provide nutrients and moisture for plants (biotic) to grow 

  • As part of photosynthesis, plants take in CO₂ and release oxygen, balancing gases in the atmosphere

• The plants (biotic) are then eaten by animals (biotic), who also eat each other 

• When the plants and animals die, the nutrients are then returned to the soil (abiotic) through decomposition

• If one component of this cycle is changed, for example, by vegetation being cut down, all the other components will be affected 

• This leads to:

  • Fewer nutrients are added to the soil through decomposition

  • There will be less food and fewer habitats, so the number of animal species will decrease

  • The soil is exposed to erosion from the sun and rain 

  • CO₂ levels will increase

  • Plants will transpire less, resulting in less precipitation

Carbon store

• Ecosystems store carbon

• The carbon is stored in:

  • Animals

  • Plants

  • Soil

  • Dead organic matter

• This storage forms part of the carbon cycle

• The amount of carbon stored in each depends on the climate

  • In tropical rainforests, large amounts of carbon are stored in the trees and vegetation (biomass)

  • In tundra areas, very little carbon is stored above ground due to the lack of vegetation

    • Instead, it is stored in the peat soil, which forms through slow decomposition due to the cold conditions