Biology - Living Things and Their Environments
This domain tests relationships between organisms and their environment: food webs, energy flow, population change, adaptation, and conservation. Niigata items often use local ecosystems such as rice paddies, the Shinano River, or Sado Island’s satoyama, where the reintroduced Japanese crested ibis depends on paddy fields and woodland edges.
Ecosystem structure
- Biotic factors are organisms; abiotic factors include light, water, temperature, and soil.
- Producers fix light energy; consumers eat; decomposers break down dead matter and recycle nutrients.
- Food-chain arrows point from the organism eaten to the eater, showing energy flow.
- A food web is more realistic than a single chain because most organisms eat several things.
Energy and matter
- Energy flows one way and is lost as heat; only about 10% passes to the next trophic level.
- Matter cycles: carbon via photosynthesis, respiration, decomposition, and combustion; nitrogen via fixation and decomposition.
- Biomass pyramids are usually upright because energy is lost at each transfer.
Populations and interactions
- Population size changes with births, deaths, immigration, and emigration; carrying capacity limits growth.
- Competition, predation, and symbiosis (mutualism, parasitism) shape communities.
- Alien species can outcompete natives; conservation requires habitat protection.
Worked example
If algae fix 10,000 kJ, how much energy reaches a heron at the fourth trophic level? Using the 10% rule: algae 10,000 → water flea 1,000 → small fish 100 → heron 10 kJ. The reasoning assumes roughly 90% loss at each transfer as heat and movement, so top predators need large areas to find enough food.
Traps
- Reversing food-chain arrows.
- Treating decomposers as a trophic level that receives all energy.
- Saying energy cycles; matter cycles, energy flows.
- Ignoring abiotic factors when explaining population change.
- Reading population graphs without checking axes.