The solution that the student used to produce the chloroplast suspension had the same water potential as the chloroplasts.

Explain why it was important that these water potentials were the same.

Explain why the student set up Tube 1.

Explain the results in Tube 3.

The student evaluated the effectiveness of different chemicals as weed-killers by assessing their ability to prevent the decolourisation of DCPIP in chloroplast suspensions.

He added different concentrations of each chemical to illuminated chloroplast suspensions containing DCPIP. He then determined the IC50 for each chemical. The IC50 is the concentration of chemical which inhibits the decolourisation of DCPIP by 50%.

Explain the advantage of the student using the IC50 in this investigation.

Explain how chemicals which inhibit the decolourisation of DCPIP could slow the growth of weeds.