This was the least popular question in this section, as candidates did not seem to be familiar with the experiment. Many candidates could not state the aim of the experiment which was “To show that Carbon dioxide is necessary for photosynthesis” They were not familiar with the word “destarched” and they could not state the procedure for the experiment or the procedure for destarching a plant. A number of candidates however could state three factors that can affect the result of the experiment.
Expected answers include:
Destarching a plant
By leaving the plant in darkness; for more than a day.
Necessity for destarching
To ensure that any starch detected at the end of the experiment(s) is formed during the experiment.
Soda lime is used to absorb carbon dioxide (from the air in the bottle).
Next step of experiment
Expose the experiment to light for some time (to allow for starch formation);
Pluck enclosed leaves and label A (with Soda lime) and B (without Soda lime);
Boil each leaf in water and then in ethanol to decolorise them;
Rinse each leaf in water to soften;
Add iodine solution to test for starch;
Leaf B turns blue-black indicating the presence of starch;
Leaf A turns yellow-brown indicating the absence of starch.
Conclusion
Carbon dioxide is necessary for photosynthesis. 
