A student investigates how the wavelength of light affects the rate of photosynthesis in spinach (Spinacia oleracea) leaves.
The student sets up the following method:
- Cut 10 leaf discs of identical size from the same healthy spinach leaf.
- Place these 10 discs into a syringe containing 0.2% sodium hydrogen carbonate solution.
- Repeat this procedure to set up a second syringe with another 10 identical leaf discs in the same solution.
- Place the first syringe directly above a blue LED light source (wavelength 450 nm450\text{ nm}450 nm).
- Place the second syringe directly above a green LED light source (wavelength 530 nm530\text{ nm}530 nm).
- Record the time taken for the leaf discs in each syringe to rise to the surface of the solution.
a.[3]
Identify three variables (other than leaf species) that the student must control to ensure that the data collected for the two light wavelengths is valid.
b.[2]
Explain the biological process that causes the leaf discs to rise to the top of the syringe.
c.[3]
Describe how the student could adapt this method to investigate the effect of temperature on the rate of photosynthesis when using the blue LED light source.