Energy Transfer in Ecosystems

This lesson covers energy flow through ecosystems, including food chains, food webs, trophic levels, productivity (GPP and NPP), and energy transfer efficiency calculations, as required by the Edexcel A-Level Biology specification (9BI0), Topic 10 -- Ecosystems.

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Energy Flow Through Ecosystems

Energy enters most ecosystems as sunlight and flows through the ecosystem via feeding relationships. At each stage, energy is transferred but also lost, primarily as heat from respiration.

Key principles:

• Energy flow is unidirectional -- it cannot be recycled
• Energy is lost at each trophic level (mainly as heat from respiration)
• Only a small percentage of energy is transferred from one trophic level to the next
• This is why food chains rarely have more than 4--5 trophic levels

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Trophic Levels

A trophic level is the position of an organism in a food chain or food web.