Ecosystems and the environment

An ecosystem is a community of living things interacting with each other and with their non-living environment.

Food chains and webs

Energy flows from the Sun to producers (green plants), then to primary consumers (herbivores), secondary consumers and so on.

Example: grass → impala → lion. Arrows show the direction in which energy flows.

Only about 10% of energy passes from one level to the next; the rest is lost as heat, movement and waste. This is why food chains are short.

Cycles

• Carbon cycle: plants take in carbon dioxide in photosynthesis; respiration, decay and burning return it to the air.
• Water cycle: evaporation, condensation, precipitation and run-off.

Human impact

• Deforestation (for firewood, farming and tobacco curing) causes soil erosion and loss of habitats.
• Veld fires destroy grazing and kill organisms.
• Pollution: litter, sewage, chemicals and mine waste damage rivers; burning fossil fuels adds carbon dioxide, contributing to climate change.
• Conservation: planting trees, contour ridges, protected areas such as Hwange and Mana Pools, and recycling.

Check yourself

1. In the food chain maize → mouse → snake → hawk, name the secondary consumer.
2. Why are food chains rarely longer than five organisms?
3. Give two effects of deforestation.