Ecology and Environment
Domain 10 covers organisms and populations, ecosystems, biodiversity and conservation. The exam tests adaptations, population growth, species interactions, energy flow, nutrient cycling and conservation strategies.
Core rules
- Exponential growth is J-shaped: dN/dt = rN. Logistic growth is S-shaped and includes carrying capacity K: dN/dt = rN(K−N)/K.
- Species interactions: mutualism (+/+), commensalism (+/0), parasitism (+/−), predation (+/−), competition (−/−).
- Energy flow is unidirectional; about 10% passes to the next trophic level. Gross primary productivity minus respiration equals net primary productivity.
- Nutrient cycles include gaseous (carbon, nitrogen) and sedimentary (phosphorus) cycles.
- Biodiversity conservation uses in situ methods (national parks, biosphere reserves) and ex situ methods (zoos, seed banks). Hotspots have high endemism and habitat loss.
Worked example
Producers fix 10,000 J. Using the 10% law, how much energy reaches tertiary consumers? Primary consumers receive 1,000 J; secondary consumers 100 J; tertiary consumers 10 J. Reasoning: at each transfer, about 90% is lost as heat and through respiration, so only about 10% is available to the next level. This limits food-chain length.
Traps
- Confusing gross and net primary productivity; NPP = GPP − respiration.
- Saying energy cycles; energy flows, nutrients cycle.
- Treating a biosphere reserve as ex situ; it is in situ.
- Assuming 10% law gives exact values in every ecosystem; it is a general approximation.