Explain the change in the rate of photosynthesis when the concentration of carbon dioxide increased between 0.00% to 0.08%.
How to approach this question
1. **Describe** the trend using the data. Look at the "Rate of photosynthesis" column as the "CO2 concentration" goes from 0.00 to 0.08. What happens to the rate?
2. **Explain** the trend. Why does this happen? Think about the word equation for photosynthesis. What role does carbon dioxide play? Use the term "limiting factor".
Full Answer
As the carbon dioxide concentration increased from 0.00% to 0.08%, the rate of photosynthesis increased. This is because carbon dioxide is a reactant (or limiting factor) for photosynthesis, so more CO2 means the reaction can happen faster.
Looking at the table, as the carbon dioxide concentration increases from 0.00% to 0.08%, the rate of photosynthesis increases from 0 to 20 arbitrary units. This is the description of the trend.
The explanation is that carbon dioxide is one of the raw materials (reactants) needed for photosynthesis. In this range, CO2 is the limiting factor – meaning its availability is what is limiting how fast the reaction can proceed. By providing more CO2, the plant can photosynthesise at a faster rate, until another factor (like light intensity or temperature) becomes the new limiting factor.
Common mistakes
✗ Only describing the trend without explaining it (e.g., "The rate goes up from 0 to 20").\n✗ Only giving the explanation without describing the trend (e.g., "CO2 is a limiting factor").\n✗ Not mentioning that CO2 is a reactant or limiting factor.
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