Trophic Levels

Energy enters ecosystems from the Sun. During photosynthesis, plants change sunlight into chemical energy (stored in glucose).

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Ecosystems need energy

• Energy flows one way in ecosystems. It’s always needed from an outside source (like the Sun) because it leaves as heat during metabolism.

• Since energy leaves as heat, ecosystems need a constant energy supply to keep going.

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Energy flows in one direction

• Matter moves through the ecosystem as organisms interact (e.g., when one eats another), these are called trophic interactions.

• Matter is conserved (it doesn’t disappear), but energy can be gained or lost.

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​Matter also moves through ecosystems

• Primary producers (like plants) start the cycling of matter in an ecosystem. They take sunlight and carbon from the air to make glucose (a type of sugar) that stores energy.

​Matter and Energy Cycle

When organisms die, their chemical elements (like carbon and nitrogen) are recycled. Decomposition breaks them down and returns them to the soil, where plants can absorb them and use them for things like photosynthesis.

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Matter and Energy Cycle

​These organisms make their own food using light or inorganic substances (like minerals). They turn this into chemical energy. The amount of food producers make shows how stable the ecosystem is.

Autotrophs (producers)

​These organisms get their food by eating other living things.

Heterotrophs

​These organisms break down nonliving organic material, like dead animals and waste. They get nutrients from things that are no longer alive and work at all trophic levels.

Decomposers

​The 10% Rule explains the energy available to each trophic

level in an energy pyramid. While inexact, this rule of thumb

suggests that at each trophic level, 90% of the available energy

is used by the organisms’ metabolism or is lost as heat. This

leaves only 10% of the original energy available for the next

trophic level.