A student isolated chloroplasts from pea leaves into a sucrose buffer solution to prepare a chloroplast suspension. She used this suspension and the redox indicator DCPIP (which is blue when oxidised and colourless when reduced) to investigate the light-dependent reactions of photosynthesis.
The student set up three test tubes as follows:
At the start, the contents of all three tubes were blue. After 25 minutes at 22 ∘C22\text{ }^\circ\text{C}22 ∘C, the contents of Tube 1 and Tube 2 remained blue, while the contents of Tube 3 turned colourless.
The sucrose buffer solution used to isolate the chloroplasts had the same water potential as the chloroplast interior. Explain why it was important that these water potentials were equal.
Explain the purpose of setting up Tube 1 in this investigation.
Explain how herbicides that inhibit the reduction of DCPIP would slow down the growth of weeds.
