Ecology, Environment, and Conservation
Levels of organisation
Ecology studies the relationships between organisms and their environment. An organism lives in a habitat; a population is all individuals of one species in an area; a community is all populations; an ecosystem includes the community plus the physical environment. Biotic factors are living (predators, disease, competition); abiotic factors are non-living (light, temperature, water, soil pH, oxygen).
Feeding relationships
Food chains begin with a producer (photosynthetic plant) and pass energy to primary, secondary, and tertiary consumers. Arrows show the direction of energy flow. Only about 10% of energy passes to the next level, so food chains rarely have more than four or five links. Decomposers break down dead matter and recycle nutrients. A pyramid of biomass shows the mass at each level and is usually wider at the base. Traps: confusing a food web with a food chain, and forgetting that energy is lost as heat and through excretion.
Cycles and human impact
Carbon cycles between atmosphere, organisms, soil, and oceans through photosynthesis, respiration, combustion, and decomposition. The greenhouse effect keeps Earth warm; human emissions of carbon dioxide and methane enhance it, causing climate change. Other issues: acid rain (sulfur and nitrogen oxides), eutrophication (fertiliser runoff causing algal blooms and oxygen depletion), deforestation, and plastic pollution.
Conservation
Biodiversity is the variety of species and habitats. Conservation protects it through nature reserves, captive breeding, seed banks, and laws. Sustainable development meets present needs without harming future generations.
Worked example
Grass → rabbit → fox. If the fox population is removed, rabbits increase, grass decreases, and eventually rabbits fall again - illustrating interdependence and carrying capacity.