Year 8 Science · Unit 1 · Lesson 23
Challenge Worksheet
Learning Goals
Find the mistake
A student wrote this answer
"Plants recycle all the CO₂ they produce back into oxygen through photosynthesis, so burning fossil fuels is completely fine because plants will just absorb the extra CO₂. In fact, more CO₂ in the atmosphere is actually good for plants, it gives them more raw material for photosynthesis, so forests will grow bigger and absorb all the carbon we produce. The carbon cycle is a natural system that automatically corrects itself, so human activity can't permanently change it."
1. Identify at least TWO specific mistakes in the student's answer. State each error clearly.
2. Rewrite the flawed section about burning fossil fuels and the carbon cycle so that it is scientifically correct. Your version should explain what actually happens to fossil fuel CO₂ in terms of the natural carbon cycle.
3. Explain why the mistake about "plants balancing fossil fuel emissions" is an easy one to make. What part of the carbon cycle does the student misunderstand, and why might a general reader find the student's version believable?
1. Fossil fuels (coal, oil and gas) are made of ancient organic matter that was buried millions of years ago. Using your knowledge of the carbon cycle, explain why burning fossil fuels disrupts the cycle in a way that natural processes like respiration and decomposition do not.
2. The nitrogen cycle requires bacteria at multiple stages. Design a brief explanation (4–5 sentences) for a primary school student that explains why we cannot just "add nitrogen from the air" directly to crops, and why we need either bacteria or synthetic fertilisers to grow food.
Wrap Up
In one sentence, what was the main idea of this lesson?