This topic summary covers Knowledge Organiser within Ecosystems Communities for GCSE Biology. Topic 1: Ecosystems Communities It is section 14 of 15 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 14 of 15
Practice
15 questions
Recall
20 flashcards
Knowledge Organiser
Key Terms
- Ecosystem: The interaction between a community of living organisms and the non-living (abiotic) components of their environment
- Community: All the populations of different species living in the same area at the same time
- Population: All the individuals of one species living in the same area at the same time
- Habitat: The place where an organism lives
- Niche: The role of an organism in its ecosystem, including what it eats, where it lives, and how it interacts with other species
- Interdependence: Species depending on each other for food, shelter, pollination, or seed dispersal — so a change to one population affects others
- Trophic level: The position an organism occupies in a food chain
Abiotic vs Biotic
- Abiotic: Temperature, light intensity, moisture, pH, wind speed, CO₂ concentration, O₂ availability, soil mineral content
- Biotic: Predation, competition (intra- and interspecific), disease, food availability, arrival of new species
- Energy transfer: approximately 10% passes between each trophic level
- ~90% of energy is lost at each level — through respiration (heat), undigested material in faeces, and urine
- Grade 7+ separator: Because only ~10% of energy transfers, a chain of 5 trophic levels means only 0.01% of the producer's original energy reaches the top predator — this is why food chains are short and why eating lower in the food chain is more energy-efficient
Must-Know Facts
- Producers (plants/algae) use light energy to make organic molecules via photosynthesis
- Food chains rarely exceed 4–5 trophic levels because too little energy remains at higher levels
- Removing one species can affect the whole community (interdependence)
- Stable communities have roughly constant populations with predator-prey numbers fluctuating in a cycle
- Decomposers (bacteria and fungi) break down dead organic matter and return mineral ions to the soil
Common Mistakes
- Writing "ecosystem = living things only": An ecosystem includes both the community of organisms AND the non-living (abiotic) environment. The AQA mark scheme requires both components — a definition that omits the abiotic environment will not score the mark.
- Confusing population, community, and ecosystem: Population = one species; community = all species in an area; ecosystem = community + abiotic factors. Examiners frequently use these terms interchangeably in student responses and award 0 when the wrong level is described.
- Only tracing food web effects in one direction: When a species declines, trace the effect UP (predators lose food source, their population decreases) AND DOWN (prey faces less predation, their population increases). One-directional answers score only 1 of 2 available marks.
- Saying "90% of energy is lost as heat": Energy is not only lost as heat — it is also lost in undigested material (faeces) and in urine. The correct answer is that energy is lost through respiration (heat), excretion, and in undigested material. Saying only "heat" will lose a mark if the question asks you to describe how energy is lost.
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Practice Questions for Ecosystems Communities
What is a community in ecology?
Explain what is meant by interdependence in an ecosystem.
Quick Recall Flashcards
What is a community?
All the populations of different species living and interacting in the same area at the same time.
What is a habitat?
The place where an organism lives — the specific part of the environment that provides everything the organism needs to survive.
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