Biology: Living Things and Their Environments
Ecology items use a food web or a pond survey and ask you to trace matter and energy, or to predict what happens when one link changes.
Structure of an ecosystem
- 生産者 (plants, algae) fix light energy by 光合成; 消費者 pass it on; 分解者 (bacteria, fungi) break down dead matter and return inorganic nutrients to the soil.
- A 食物連鎖 is a single chain; a 食物網 shows that most consumers eat several things, so removing one species does not automatically collapse the web.
- Energy is lost as heat and in excretion at each step, so the biomass of each level is much smaller than the one below.
Cycles
- 炭素: 光合成 removes CO₂; 呼吸 and decomposition release it; combustion releases it.
- 窒素: 窒素固定 by 根粒菌 in legume roots and by lightning converts N₂ into usable compounds; decomposers return nitrogen to the soil.
Humans and environment
外来種 outcompete natives; 森林破壊 and 水質汚染 reduce 生物多様性; 富栄養化 causes algal blooms and oxygen depletion.
Worked example. A pond chain: 植物プランクトン → ミジンコ → 小魚 → 大型魚. If the phytoplankton store 5000 kJ and roughly 10 % passes to each level, the ミジンコ receive 500 kJ, the 小魚 50 kJ and the 大型魚 5 kJ. Remove the 小魚 and the ミジンコ rise at first while the 大型魚 decline - name the direction of each effect, not just 'the balance is lost'.
Traps. Calling decomposers consumers; saying energy is recycled (matter cycles, energy flows); assuming a larger population always means more energy; ignoring the alternative links a food web provides.