Ecology and Environmental Science
What this domain tests
Ecology and Environmental Science tests ecosystems, energy flow, nutrient cycles, species interactions, pollution and conservation.
Core rules
- Organism → population → community → ecosystem. A habitat is where an organism lives.
- Food chains start with producers. Arrows show the direction of energy flow to the consumer.
- Only about 10% of energy passes to the next trophic level. The rest is lost as heat, used in movement or excreted.
- A pyramid of numbers can be inverted, but a pyramid of energy is always upright.
- Carbon cycle: photosynthesis removes carbon dioxide; respiration, combustion and decomposition release it.
- Nitrogen cycle: nitrogen fixation, nitrification, assimilation and denitrification.
- Pollution: greenhouse gases cause global warming; sulfur dioxide and nitrogen oxides cause acid rain; excess fertiliser causes eutrophication.
- Conservation protects biodiversity and habitats.
Worked example
A grassland producer stores 10 000 kJ m⁻² yr⁻¹. At 10% transfer, primary consumers receive 1000 kJ, secondary consumers 100 kJ and tertiary consumers 10 kJ. A top predator therefore needs a large area, and food chains rarely have more than five trophic levels because too little energy remains.
Traps
Do not point arrows from consumer to producer. Do not count decomposers as a trophic level in a grazing food chain. Do not say energy is recycled; nutrients are recycled, but energy flows one way. Distinguish global warming from ozone depletion.