Ammonia is a gaseous pollutant released from agricultural activities. Ammonia dissolves in water on leaf surfaces to make an alkaline solution. Scientists think that this might harm plants by affecting photosynthesis.
Photosynthesis is controlled by enzymes.
Which two statements explain how an alkaline solution could affect photosynthesis?
- Alkaline solution will increase the pH and cause the enzyme to change shape.
- Alkaline solution will decrease the pH and cause the enzyme to change shape.
- Alkaline solution will decrease the pH and cause the substrate to change shape.
- The enzyme will not fit into the active site of the substrate.
- The substrate will denature.
- The substrate will not fit into the active site of the enzyme.
Students take some geranium leaves and spray them with water containing different concentrations of ammonia.
They then measure the rate of photosynthesis of the leaves.
The graph shows their results.
The students plotted the rate of photosynthesis as a percentage of the rate in a control experiment. The control experiment involved spraying the leaves with a different substance. Suggest what substance the students used to spray the leaves as a control.
One of the students makes this conclusion:
'The results of our experiment show that ammonia is affecting the plant and it is doing this because it forms an alkaline solution.'
Discuss whether this is a reasonable conclusion to make from the students' results.
Suggest how the students could modify their experiment to prove that ammonia is affecting the plant because it forms an alkaline solution.