Ecology and the Environment
This domain covers ecosystems, energy flow, nutrient cycles and sampling. The exam tests whether you can interpret food chains and pyramids, explain human effects, and use sampling data quantitatively.
Ecosystems and energy
A habitat is where an organism lives; a population is one species in an area; a community is all populations; an ecosystem includes the physical environment. Food chains begin with producers. Arrows show energy transfer. Energy is lost through respiration, heat, movement, excretion and uneaten parts, so only about 10% passes to the next level. Decomposers break down dead material and return nutrients.
Cycles and sampling
The carbon cycle includes photosynthesis, respiration, combustion and decomposition. Random quadrats estimate population size; transects show distribution along a gradient. Capture–recapture assumes no migration, no death between samples, and that marks do not affect survival.
Worked example
A quadrat of 0.25 m² contains a mean of 6 daisies. A field is 100 m². Density = 6 ÷ 0.25 = 24 daisies per m². Estimated total = 24 × 100 = 2400 daisies. Show the division and the multiplication; a common error is multiplying by 0.25 instead of dividing.
Traps
- Energy is not recycled; nutrients are.
- Decomposers are not usually the first trophic level.
- A pyramid of biomass can look inverted if measured at one moment.