Our Environment
This domain tests ecosystem structure, food chains and webs, energy flow and the 10% law, biomagnification, ozone depletion, and waste management.
Ecosystems and energy
An ecosystem has biotic components (producers, consumers, decomposers) and abiotic factors such as light, temperature, water and soil. Green plants are producers; herbivores are primary consumers. A food chain shows one path of energy flow, a food web shows the many links, and each step is a trophic level.
The 10% law
Only about 10% of the energy at one trophic level passes to the next; the rest is lost as heat and in life processes. This is why food chains rarely have more than four or five levels and why top consumers are few.
Worked example
Producers fix 10,000 J. Primary consumers receive 1,000 J, secondary consumers 100 J, tertiary consumers 10 J, and a quaternary consumer only 1 J. This explains why a large area of plants supports only a small number of top predators.
Pollution issues
- Non-biodegradable substances such as DDT and mercury accumulate along food chains - biomagnification - reaching the highest concentrations in top consumers, including humans.
- CFCs from refrigerants and aerosols break down stratospheric ozone and let harmful ultraviolet radiation through; the Montreal Protocol phased them out.
- Carbon dioxide, methane and CFCs are greenhouse gases; excess carbon dioxide warms the atmosphere.
- Sewage adds nutrients and causes eutrophication; industrial effluents add heavy metals; plastic persists for centuries.
- Management: segregate waste, compost biodegradable matter, recycle, treat sewage before release, and prefer paper and cloth bags.
Traps
Energy flows one way and is not recycled, whereas nutrients are recycled; decomposers are not consumers; the ozone hole and global warming are separate problems with different causes.