The effect of the presence or absence of chlorophyll on photosynthesis can be investigated using a variegated plant. Variegated plants have regions of their leaves with, and without, chlorophyll.
Only those areas of the leaf with chlorophyll photosynthesise. They will test positive for starch, which is built up from the glucose produced.
To investigate photosynthesis in areas of a leaf with and without chlorophyll
Care must be taken when using boiling water.
Care must be taken when using boiling ethanol. Make sure that no Bunsen burners are turned on as the ethanol is highly flammable.
Iodine solution is an irritant.
Eye protection must be worn.
Starch is produced from glucose made during photosynthesis. Areas of the leaf with chlorophyll should turn blue–black when iodine is added proving starch is present. This in turn, proves that photosynthesis occurred. The white areas of the leaf without chlorophyll could not photosynthesise. This means they could not produce glucose and turn this to starch. So, when tested with iodine, these areas should remain pale.