This memory aid covers Memory Aids within Ecosystems Communities for GCSE Biology. Topic 1: Ecosystems Communities It is section 9 of 12 in this topic. Use it for quick recall, then test yourself straight afterwards so the memory aid becomes usable in an answer.
Topic position
Section 9 of 12
Practice
15 questions
Recall
20 flashcards
Memory Aids
Trophic level order — "Poking Carrots Helps Everyone":
- Producers (plants, algae — photosynthesise)
- Consumers — Primary (herbivores)
- High consumers — Secondary and tertiary (carnivores)
- Energy — only ~10% transfers to each level
Abiotic vs Biotic — the "A" rule: Abiotic = Absent of life (temperature, light, pH, moisture, wind, CO2). Biotic = Biological (predation, competition, disease, food). If it was once alive or IS alive, it is biotic. If it was never alive, it is abiotic.
Population vs Community — "One vs All": Population = ONE species; Community = ALL species. Think: one popstar vs the whole music community.
Quick Check: In a grassland ecosystem, a disease wipes out 80% of the rabbit population. Using your knowledge of food webs and interdependence, predict and explain the likely effects on (a) the fox population and (b) the grass population over the following year.
(a) The fox population would initially decrease. Foxes depend on rabbits as a major food source. With 80% fewer rabbits, there is insufficient prey to sustain the current fox population — foxes will compete more intensely for remaining rabbits and other prey. Death rates will rise and birth rates will fall, reducing the fox population. (b) The grass population would initially increase. Rabbits graze on grass, so with far fewer rabbits, less grass is consumed. Grass can grow unchecked, spreading to fill available space. However, if other herbivores (e.g., mice, deer) respond to the increased grass by reproducing, grass may later return to previous levels. This illustrates interdependence — a change to one population has knock-on effects throughout the food web.
Quick Check: A student claims: "In a food chain with four trophic levels, the top carnivore receives about 40% of the energy originally fixed by the producers." Evaluate this claim using your knowledge of energy transfer efficiency.
The claim is incorrect. Only approximately 10% of energy is transferred between each trophic level. After the first transfer (producers to primary consumers) only 10% remains. After the second transfer (primary to secondary consumers) only 10% of that 10% = 1% remains. After the third transfer (secondary to tertiary consumers/top carnivore) only 10% of 1% = 0.1% of the original energy remains. The other 90% is lost at each step, mainly as heat released during respiration by the organisms at each trophic level. The student has confused the percentage transferred (10%) with cumulative percentage, and has dramatically overestimated energy transfer efficiency.
Quick Check: A farmer applies a pesticide that kills all insects in a wheat field. Using your knowledge of abiotic and biotic factors and interdependence, explain two unintended ecological consequences that could result from this action.
Consequence 1 — Loss of pollinators: Many insects are pollinators (e.g., bees). Without insect pollination, flowering plants including wildflowers around the field cannot reproduce sexually, reducing plant diversity and the food available for other herbivores. Consequence 2 — Reduced food for insectivores: Birds and mammals that feed on insects (e.g., hedgehogs, swallows) lose a major food source. Their populations decline, which in turn affects their predators. Both consequences illustrate biotic interdependence — altering one population (insects) ripples through the food web — and how human interventions (abiotic change: pesticide alters soil/water chemistry) can fundamentally destabilise an ecosystem.