1. We take a potted plant like croton whose leaves are partly green and partly white. The green part of the leaf has chlorophyll but the white part of the leaf does not have chlorophyll.
2. Place this plant in a completely dark place for about three days to destarch its leaves.
3. Take out the potted plant from the dark place and keep it in bright sunshine for three to four days.
4. Pluck the variegated leaf from the plant, boil it in water for a few minutes and then remove its green colour ‘chlorophyll’ by boiling it in alcohol. The green parts of the leaf get decolourised. So, we get decolourised leaf.
5. Wash the decolourised leaf with hot water to soften it and remove any chlorophyll which may be sticking to it.
6. Pour iodine solution over the colourless leaf and observe the change in colour of the leaf.
7. We will find that the outer part of leaf that was originally white (without chlorophyll) does not turn blue-black on adding iodine solution showing that no starch is present in this outer part of the leaf. From this observation we conclude that the photosynthesis to make starch does not take place without chlorophyll.
8. The inner part of leaf which was originally green (contained chlorophyll) turns blue-black on adding iodine solution showing that starch is present in this inner part of the leaf. From this observation we conclude that the photosynthesis to make starch takes place in the presence of chlorophyll. In other words, chlorophyll is necessary for the process of photosynthesis to take place.