Environment: Concepts, Components and Ecosystem Structure
What this domain tests
The Environment: Concepts, Components and Ecosystem Structure domain checks whether you can define environment and ecology precisely, classify biotic and abiotic components, and trace energy and matter through an ecosystem. Expect questions on trophic levels, ecological pyramids, productivity, nutrient cycles and succession - and definitions that sound similar but are not interchangeable.
Core rules and concepts
- Environment is the sum of all biotic and abiotic conditions around an organism; ecology studies interactions between organisms and their surroundings.
- Abiotic components include light, temperature, water, air, soil and nutrients; biotic components are producers, consumers and decomposers.
- Energy flow is unidirectional and non-cyclic; matter cycles through biogeochemical cycles such as carbon, nitrogen, phosphorus and water.
- Lindeman's 10% law: roughly 10% of energy at one trophic level is transferred to the next; the rest is lost as heat, in respiration and in faeces.
- GPP is total solar energy fixed; NPP = GPP − respiration.
- Pyramids of numbers and biomass can be inverted (e.g., phytoplankton in an ocean); the pyramid of energy is always upright.
- Succession proceeds from pioneer to climax communities; hydrarch succession starts in water, xerarch on dry rock.
Worked example
A grassland has GPP of 10,000 kcal m⁻² yr⁻¹ and producer respiration of 4,000 kcal. NPP = 10,000 − 4,000 = 6,000 kcal. Herbivores assimilate 10% of NPP = 600 kcal; secondary consumers = 60 kcal; tertiary consumers = 6 kcal. Reasoning: subtract respiration first, then apply the 10% law one trophic step at a time. The calculation is an ecological approximation, not a conservation law.
Traps that cost marks
Calling energy flow cyclic; treating GPP and NPP as synonyms; assuming every biomass pyramid is upright; counting decomposers as a separate consumer trophic level in every food chain; forgetting that the 10% law applies to energy, not biomass or numbers.