Natural Resources and Environment
Natural resources and environment questions ask how ecosystems move energy and matter, how human activity affects air, water, soil and biodiversity, and how resources can be managed sustainably. The exam favours food chains, the 10% law, pollution, ozone depletion and conservation measures.
Core rules and concepts
- Energy flows from producers to consumers in one direction; nutrients cycle.
- About 10% of energy passes to the next trophic level; the rest is lost mainly as heat.
- Food chains are short because available energy falls sharply at each level.
- Non-biodegradable pollutants such as some pesticides can biomagnify along a food chain.
- The ozone layer absorbs ultraviolet radiation; chlorofluorocarbons destroy ozone.
- The greenhouse effect is natural warming; excessive greenhouse gases enhance it.
- Sustainable management includes the 3Rs, rainwater harvesting, check dams, afforestation and protection of biodiversity.
Worked example
Grass in a field contains 10,000 kJ of energy. A deer eats the grass and a tiger eats the deer. Using the 10% law, the deer receives 1,000 kJ and the tiger receives 100 kJ. This explains why top predators are few and need large areas. It also explains why a food chain with many levels cannot support a large top-carnivore population.
Traps that cost marks
- Confusing ozone depletion with global warming; they have different causes and effects.
- Saying energy is recycled in an ecosystem; matter cycles, energy does not.
- Reversing the arrows in a food chain; arrows show the direction of energy transfer.
- Treating all waste as biodegradable.
- Assuming dams have only benefits and ignoring displacement and siltation.