Ecosystem Basics

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An ecosystem is a set of relationships between all the organisms and non-living factors in a particular area, e.g. a forest ecosystem includes trees, animals and microorganisms as well as the water, soil, rock and air.

The organisms that live there are called biotic factors and the non-living objects are abiotic factors.

The organisms depend on physical factors and each other to survive, so relationships between organisms are important.

Ecosystes vary in size- they can be small (a pond) or large (a forest, mountainside or ocean).

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A biome is an are with distinctive climate and vegetation, e.g. a tropcial rainforest or arctic tundra.

Biomes can contain different ecosystems, e.g. within a tropical grassland biome there could be areas of open woodland, areas of swamp, lakes and grassland plains.

Biomes usally cover a large area, often spanning multiple countries.

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Energy moving between organisms

Energy enters an ecosystem by photosynthesis- plants use energy from sunlight to grow and reproduce.

The energy is stored in plants and passed up the food chain when the plant is eaten.

This process continues throughout the ecosystem- when one organism eats another it receives the energy from that organism. This means that energy flows between all the organisms in an ecosystem.

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Food chains and food webs

Each stage in a food chain or web is called a trophic (feeding) level

Producers (autotrophs, e.g. plants) occupy the first trophic level. They make their own food.

Primary consumers (herbivores or omnivores) occupy the next level- they eat producers.

Secondary consumers (carnivores and omnivores) occupy the next level- they eat consumers.

Tertiary consumers (top carnivores and omnivores) occupy the next level- they eat consumers.

Biomass (total mass of living matter) decreases at each trophic level e.g. a field of dandelions feeds a family of rabbits, which can all be scoffed one hungry fox.

Food chains show one way the energy from a producer is passed to a consumer.

Food webs show multiple food chains and demonstrate different ways energy flows through an ecosystem.

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Energy being lost

The amount of energy at each trophic level decreases as you go up the trophic levels.

Around 90% of energy is lost at each trophic level.

  • Less than 50% of sunlight is actually used in photosynthesis. for example:

-Some will fall on areas of the plant that don't photosynthesise, e.g. the stem or trunk.

-The plant can only use certain wavelengths of light

  • Only about 10% of energy stored by the autotrophs is passed on to herbivores, and 10% of the energy stored by the berivores is passed on to the carnivores:

-Some parts of the organism aren't eaten, e.g. the roots, bones or fur, and not all of what is eaten is used for energy

-Some energy is ost as waste, e.g. droppings

-Consumers use some of the energy for movement  and generating body heat, so it's not passed on

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Nutrients being recycled

Living organisms need large quantities of carbon, hydrogen, oxygen, nitrogen and sulfur.

These elements are constantly being recycled between plants, animals and the atmosphere.

1) Plants take carbon dioxide from the air and nutrients from the soil, e.g. nitrogen. They use these to create plant material.

2) These nutrients get passed along food chains by feeding.

3) When plants and animals die they're broken down by decomposers (e.g.bacteria). Nutrients (e.g. nitrogen) are returned to the soil to be used again by plants.

4)Plants, animals and decomposers all release carbon dioxide back into the air through respiration.

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