Ecosystems and Food Chains

Key terms

• Ecosystem – all the organisms and the non-living conditions in an area.
• Population – all members of one species in an area.
• Community – all the populations together.
• Habitat – where an organism lives.

Food chains

Show energy transfer, always starting with a producer (usually a plant that photosynthesises):

grass → rabbit → fox
(producer → primary consumer → secondary consumer)

Arrows show the direction of energy flow.

Energy transfer

Only about 10% of energy passes to the next level (the rest is lost as heat, movement and waste/egestion) — which is why food chains are usually short.

Interdependence

Species depend on each other for food, shelter, pollination and seed dispersal. Removing one species affects many others (e.g. predator–prey cycles).

Cycles

• Carbon cycle: photosynthesis removes CO₂; respiration, combustion and decay return it.
• Water cycle: evaporation → condensation → precipitation.
• Decomposers (bacteria/fungi) recycle nutrients back to the soil.

Exam tip

Food-chain arrows point towards the organism doing the eating — they show energy flow. Remember the ~10% energy transfer between levels.