The Carbon Cycle

The question

How to approach this process diagram question

A process diagram shows how something is made or how a cycle works. Describe the stages in order, using sequence language and the passive voice.

1. Say what process the diagram shows and how many stages it has.
2. Overview: the number of stages, where it starts and ends, and whether it is a cycle or a straight line.
3. Describe every stage in order (First, Next, After that, Finally) mostly in the passive: the grain is crushed.
4. Do not add opinions or explain why; describe what happens.

How to plan this answer

Structure

1. Overview: state that the carbon cycle has five stages arranged in a circle, with no clear start or end point, and that burning fuels links back to photosynthesis.
2. Paragraph 2: describe the stages in the order of the arrows, starting from photosynthesis and moving clockwise through feeding, respiration and decay.
3. Paragraph 3: explain the final part of the loop, where burning fuels returns carbon to the atmosphere and the cycle repeats.
4. Keep the explanation of the loop as a cycle and avoid calling any stage the last one.

Key features to spot

• Stage 1 is photosynthesis, shown as a young green plant with the sun above it, where plants take in carbon dioxide and produce sugars.
• Stage 2 is feeding, shown as a grazing cow, which passes carbon from plants into animals through their diet.
• Stage 3 is respiration, shown as a pair of lungs with arrows leaving them, which returns carbon dioxide to the air.
• Stage 4 is decay, shown as a rotting log with a mushroom, where dead material breaks down and releases carbon into the soil.
• Stage 5 is burning fuels, shown as a fire on a heap of coal, which releases carbon into the atmosphere and connects back to photosynthesis.
• The arrow from burning fuels to photosynthesis shows that the cycle repeats, so the process does not have a beginning or an end.

Useful vocabulary

• forms a cycle: The five stages form a cycle, with carbon passing from one stage to the next.
• is absorbed by: Carbon dioxide is absorbed by plants during photosynthesis.
• is passed on to: Carbon is passed on to animals when they feed on plants.
• is released into: Carbon dioxide is released into the air during respiration.
• is returned to: Carbon is returned to the soil through decay.
• is emitted when: Carbon is emitted when fuels are burned.
• leads back to: Burning fuels leads back to photosynthesis, which completes the loop.
• repeats: The cycle repeats continuously, so carbon moves between living things and the air.
• in a clockwise direction: The stages are arranged in a clockwise direction around the circle.
• passes from ... to: Carbon passes from the plant to the animal when the cow eats grass.

Common mistakes

• Describing the process as having a start and an end, when the arrows form a closed circle with no first or last stage.
• Stating that burning fuels is the final stage of the cycle; it is the fifth stage, and its arrow leads back to the first.
• Describing photosynthesis as the cow's activity, or assigning feeding to the plant, which mixes up the roles of the two pictures.
• Omitting the explanation of why the cycle repeats, which is the specific feature the task asks candidates to show.
• Adding scientific detail such as chemical equations, which goes beyond the diagram and is not required for this task.

Examiner tip: Explain that the arrows form a loop and that burning fuels links back to photosynthesis, so the answer shows the cycle rather than a straight line.