Photosynthesis · Grade 11
In Grade 11 you learn: limiting factors and the symbol equation; the two stages of photosynthesis.
Plants make their own food. In their leaves they use energy from light to turn carbon dioxide and water into glucose, giving out oxygen. Almost every food chain starts here, and the oxygen you breathe was made this way. How fast it happens depends on light, carbon dioxide and temperature.
Key facts
- Symbol equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Photosynthesis is endothermic: energy is taken in from light.
- Limiting factors: light intensity, carbon dioxide concentration and temperature. Whichever is in shortest supply limits the rate. Too hot, and the enzymes are denatured.
Worked examples
Example 1
A piece of pondweed gives off 48 bubbles of oxygen in 4 minutes. What is the rate of photosynthesis in bubbles per minute?
Answer: 12 bubbles per minute
Example 2
The graph shows the rate of photosynthesis as light intensity increases. Why does the rate stop rising?
Answer: something else (carbon dioxide or temperature) has become the limiting factor