A student investigates the rate of photosynthesis in leaves of the same species of plant grown under two different environmental conditions: direct sunlight (sun leaves) and shade (shade leaves).
The student's method:
- Cut 10 leaf discs from a sun leaf.
- Place the discs into a syringe containing sodium hydrogen carbonate solution.
- Repeat this using 10 leaf discs from a shade leaf.
- Record the time it takes for the leaf discs to rise to the top of each syringe.
a.[3]
Give three variables that the student must control to ensure that the data collected for the two types of leaves is valid.
b.[2]
Explain why the leaf discs rise to the top of the syringes.
c.[3]
Describe how the student could adapt this method to investigate the effect of carbon dioxide concentration on the rate of photosynthesis for the sun leaves.