Environmental Science: Ecosystems, Pollution and Resources
Environmental Science covers ecosystems and energy flow, pollution and atmospheric change, and management of natural resources such as forests, water, coal and petroleum. Answers should use ecological terms precisely rather than everyday wording.
Ecosystems and energy flow
Producers → herbivores → carnivores, with arrows pointing to the eater to show energy transfer. Only about 10% of energy passes to the next trophic level; most is lost as heat in respiration. Food webs are more stable than single chains, and decomposers return nutrients to the soil. Biodegradable wastes are broken down by microbes, while plastics and DDT are non-biodegradable and accumulate along food chains (biomagnification).
Pollution and atmosphere
Carbon dioxide, methane and CFCs are greenhouse gases; excess causes global warming. CFCs release chlorine in the stratosphere and destroy ozone, which shields life from UV-B, so the Montreal Protocol phases them out. Acid rain comes from SO₂ and NOₓ. Water pollution is indicated by BOD, and nutrient runoff causes eutrophication.
Resource management
Sustainable use meets present needs without harming future supply. The Chipko movement protected Himalayan forests, joint forest management involves local communities, and rainwater harvesting or check dams recharge groundwater. Fossil fuels are non-renewable; alternatives include solar, wind, biogas and tidal energy.
Worked example
If producers in a food chain fix 10,000 kJ of energy, how much reaches a tertiary consumer? Apply the 10% law at each transfer: 10,000 kJ to primary consumers, 1,000 kJ to secondary consumers, then 100 kJ, and 10 kJ to the tertiary consumer. Reasoning: roughly 90% is lost as heat at each step, so long chains support fewer top predators and cannot sustain large populations of them.
Traps that cost marks
Reversing arrow direction in a food chain; confusing the ozone hole with the greenhouse effect; labelling every waste biodegradable; mentioning CFCs without their ozone link; treating coal and petroleum as renewable.