Environment, Natural Resources and Conservation
This domain tests how energy and matter move through ecosystems, how resources are used and misused, and how conservation works in practice. Expect questions on trophic levels with the 10 per cent law, the difference between the carbon and nitrogen cycles, renewable versus non-renewable resources, and pollution types with their effects.
Ecosystem structure and energy flow
- Components: abiotic factors plus producers, consumers and decomposers.
- Food chain and food web; each step is a trophic level.
- Lindeman's 10 per cent law: only about 10 per cent of energy passes to the next level, so energy pyramids are always upright and food chains are short.
- Energy flow is unidirectional; matter cycles.
Cycles and resources
- Carbon cycle: photosynthesis removes carbon dioxide, respiration and combustion return it; fossil fuels are a stored carbon sink.
- Nitrogen cycle: fixation (Rhizobium in root nodules, Azotobacter free-living, cyanobacteria), nitrification, assimilation, denitrification.
- Renewable: solar, wind, water, biomass. Non-renewable: coal, petroleum, minerals.
Pollution and conservation
- Greenhouse gases (carbon dioxide, methane, nitrous oxide, CFCs) trap heat; CFCs also destroy stratospheric ozone. Sulphur dioxide and nitrogen oxides cause acid rain.
- Conservation: in situ (national park, sanctuary, biosphere reserve) and ex situ (zoo, seed bank, botanical garden); joint forest management, rainwater harvesting, sustainable development.
Worked example
Grassland producers hold 20,000 kJ. Using the 10 per cent law, primary consumers receive 2,000 kJ, secondary consumers 200 kJ, tertiary consumers 20 kJ and a fourth-level carnivore only 2 kJ. A top predator therefore needs a huge producer base, which is why long food chains are rare.
Traps that cost marks
- Energy pyramids cannot be inverted; pyramids of number sometimes can.
- The greenhouse effect and ozone depletion are separate problems.
- Decomposers are not a trophic level of the grazing food chain but are essential recyclers.