Grade 11 · Life Sciences
Photosynthesis
Revise the inputs, products, location and limiting factors of photosynthesis.
Inputs and products
Photosynthesis uses light energy to make glucose from carbon dioxide and water. Oxygen is released. Chlorophyll absorbs light; chloroplasts are the organelles in which photosynthesis occurs.
Limiting factors
Light intensity, carbon dioxide concentration and temperature can limit the rate. Increasing one factor only helps until another factor becomes limiting. Very high temperatures can reduce the rate by affecting enzymes.
Formula sheet
- 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (light and chlorophyll)
Worked example
Why does the rate stop increasing when light intensity rises beyond a certain point?
- At low light intensity, light may be the limiting factor.
- As light increases, the rate rises if other conditions are suitable.
- At the plateau, another factor such as carbon dioxide availability limits the rate.
Try it yourself
1. Which gas is taken in for photosynthesis? Check answer
Carbon dioxide.
2. Why is a leaf boiled in ethanol during a starch test? Check answer
To remove chlorophyll so the iodine colour change can be seen. Ethanol is heated in a water bath because it is flammable.
Common mistake: Plants also respire. Photosynthesis and cellular respiration are different processes.