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Introduction to ecosystems

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What is an ecosystem?

The deciduous forest ecosystem
The deciduous forest ecosystem

An ecosystem is a natural system made up of biotic components (living organisms) such as plants, animals, fungi/bacteria, and abiotic components (non-living organisms) such as water, air, soil, rocks and climate. There are complex relationships that take place within ecosystems, and they are delicately balanced. 

Ecosystems can operate on a range of scales, from the small ecosystems found in hedgerows and ponds to the major biomes found across the globe, such as tropical rainforests and hot deserts.

How does energy flow within an ecosystem?

Energy flows between producers, consumers and decomposers through an ecosystem.

The cycle starts with producers, such as trees, producing their food using the sun’s energy through photosynthesis.

These producers are eaten by primary consumers, such as insects and small animals, such as rabbits. These animals are herbivores, so they only eat plants – herbivores also include larger animals such as zebras, giraffes and elephants.

These primary consumers are then eaten by secondary consumers, which tertiary consumers may eat. Tertiary are often carnivores, so only eat meat.

Animals that eat both meat and plants are known as omnivores.

You can see this flow of energy in a food chain in the image below, which shows the relationship between producers and consumers.

A simple food chain

Food webs are made up of several food chains and show the complex relationships with an ecosystem.

The nutrient cycle

Decomposers, such as fungi and bacteria, break down dead plants and animals, and the waste of other organisms. When dead material is decomposed nutrients are released back into the soil, which are then taken up from the soil by plant roots, to help plant growth. Over time these plants will drop leaves back to the ground, to once again be eaten by animals or to be broken down, releasing nutrients back into the soil. 

Decomposers are essential for all ecosystems – without them, plants would not get essential nutrients, and dead organic matter would pile up. Decomposers work best in hot damp conditions – which is why plants grow rapidly and in abundance in the tropical rainforest but hardly grow in cold environments like the tundra.

What might the examiner ask?

Explain how the Hadley cell works and why air sinks at 30 degrees N/S, what this causes (high pressure) and how high solar insolation gives high temperatures, forming an area of dry, warm deserts.

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