Build ecosystem vocabulary, food webs and photosynthesis
Learn the ecosystem terms and processes that underpin environmental management, from biotic interactions to photosynthesis and carbon stores.
Section Paper 1 · Section A · Structured questions
Exam scope and assessment notes
Original StudyForA teaching and practice, not Cambridge-authored questions, mark schemes or official grades. Cambridge expects candidates to study all eight topics, carry out investigative work and learn teacher-selected case studies. This course does not replace a centre's named case-study examples, current local environmental data, supervised fieldwork or the candidate's own investigation. Practice datasets are illustrative, not observations from a real place. No official assessment or certification is provided. The examples and practice datasets in these lessons are fictional and formative; learners must add their centre's verified case studies and current local evidence.
Before you begin
- Cambridge recommends prior environmental/science study equivalent to IGCSE or O Level. This is an AS-only qualification; use the exam-year syllabus and confirm centre entry details.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What makes environmental evidence useful?
What you will learn
- Define ecosystem organisation and identify biotic and abiotic components
- Explain photosynthesis, its limiting factors and carbon storage
- Build food chains and link energy transfer and respiration to the carbon cycle
Name the parts of an ecosystem
A biome is a major regional ecosystem; an ecosystem includes organisms and their physical environment. A population is one species in an area, a community is interacting populations, a habitat is where an organism lives and a niche is its role and resource use.
Biotic components include producers, primary, secondary and tertiary consumers, decomposers and interacting species. Abiotic factors include temperature, humidity, water, oxygen, salinity, light and pH. Competition, grazing and predation can affect organism numbers and diversity.
Photosynthesis links energy and carbon
Photosynthesis uses light energy captured by chlorophyll to make glucose from carbon dioxide and water. Word equation: carbon dioxide + water → glucose + oxygen. Chemical equation: 6CO2 + 6H2O → C6H12O6 + 6O2. Water, carbon-dioxide concentration and light availability can limit its rate.
Photosynthesis on land and in oceans transfers carbon into living material and helps form carbon stores. Producers begin food chains; energy passes through trophic levels and is lost through respiration, waste and material that is not eaten.
Respiration returns carbon
Aerobic respiration breaks down glucose in cells and releases energy, carbon dioxide and water. Word equation: glucose + oxygen → carbon dioxide + water. Chemical equation: C6H12O6 + 6O2 → 6CO2 + 6H2O.
In the syllabus carbon cycle, carbon moves through photosynthesis, feeding, respiration, decomposition, fossilisation and combustion. A cycle diagram should label both the carbon stores and the process on each arrow.
Sources for this lesson
Pause and explain
Which process transfers carbon dioxide into producer biomass?
Worked example
In a shaded pond, aquatic plants grow slowly even though nutrients are available. Explain two possible limiting factors and one carbon-cycle link.
Show the worked solution
- Identify factors that limit photosynthesis in the syllabus.
- Explain how the limiting condition affects the rate.
- Connect photosynthesis to a carbon store.
Answer Light availability may limit photosynthesis in shade; water or carbon-dioxide availability can also matter. A lower photosynthetic rate reduces glucose production and carbon transfer into plant biomass. Aquatic photosynthesis is one way carbon enters living material and a biological store.
Try a topic test
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Write the word and balanced chemical equations for photosynthesis, then name its three syllabus limiting factors.
Give me a hint
Check that the number of each atom is the same on both sides.
Compare my reasoning
- Identify the relevant data, place or process in the prompt.
- Apply define ecosystem organisation and identify biotic and abiotic components to the stated context.
- Explain the inference and one limitation or trade-off.
Word equation: carbon dioxide + water → glucose + oxygen. Chemical equation: 6CO2 + 6H2O → C6H12O6 + 6O2. The limiting factors named in the syllabus are water availability, carbon-dioxide concentration and light availability.
Look for these in your work
- Define ecosystem organisation and identify biotic and abiotic components
- Uses relevant evidence and explains the environmental mechanism
- Distinguishes observation, inference and limitation
Construct a four-level food chain from a producer to a tertiary consumer and explain one way energy is lost between levels.
Give me a hint
Begin with a photosynthetic producer and keep feeding direction clear.
Compare my reasoning
- Identify the relevant data, place or process in the prompt.
- Apply explain photosynthesis, its limiting factors and carbon storage to the stated context.
- Explain the inference and one limitation or trade-off.
One valid chain is grass → grasshopper → frog → snake: grass is the producer, grasshopper the primary consumer, frog the secondary consumer and snake the tertiary consumer. Energy is lost through respiration, waste or uneaten material, so less is available at the next trophic level.
Look for these in your work
- Explain photosynthesis, its limiting factors and carbon storage
- Uses relevant evidence and explains the environmental mechanism
- Distinguishes observation, inference and limitation
Write the aerobic-respiration equations and describe one route by which carbon returns to the atmosphere.
Give me a hint
Start with glucose and oxygen; include the products specified in the syllabus.
Compare my reasoning
- Identify the relevant data, place or process in the prompt.
- Apply build food chains and link energy transfer and respiration to the carbon cycle to the stated context.
- Explain the inference and one limitation or trade-off.
Word equation: glucose + oxygen → carbon dioxide + water. Chemical equation: C6H12O6 + 6O2 → 6CO2 + 6H2O. Respiration by organisms returns carbon dioxide to the atmosphere; decomposition and combustion also return stored carbon through different pathways.
Look for these in your work
- Build food chains and link energy transfer and respiration to the carbon cycle
- Uses relevant evidence and explains the environmental mechanism
- Distinguishes observation, inference and limitation
Common mistakes
- Confusing a community with its physical habitat
- Treating energy as recycled through an ecosystem like carbon
- Writing photosynthesis or respiration equations with atoms unbalanced
What can you explain now?
Which process transfers carbon dioxide into producer biomass?
Compare with the explanation
Photosynthesis
Photosynthesis uses light energy to form glucose from carbon dioxide and water.
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Make it stick
How does photosynthesis move carbon into living biomass, and how can respiration move it back?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.