A variegated leaf with green and yellow patches in used for an experiment to prove that chlorophyll is required for photosynthesis. Before the experiment, the green portions (A), and the pale-yellow portions (B) are observed. What will be the colour of ‘A’ just before and after the starch test? Also write the equation of photosynthesis and mark, as well as validate from which molecule the by-product is obtained.
A variegated leaf is a type of leaf which is a normal green coloured leaf but contains some patches of yellow which are devoid of chlorophyll.
1. Region A which is green in colour contains chlorophyll. However, for the starch test, the chlorophyll of the leaf needs to be removed which can be done by heating the leaf in alcohol.
2. So, the colour of the leaf before the starch test if pale yellow and after the starch test, the colour becomes blue-black as the iodine reacts with the starch present in the leaf to give blue-black colour.
3. Photosynthesis is a biochemical and a photochemical process through which all the green plants make their own food that is glucose.
4. Photosynthesis is one of the major processes which is primarily responsible for the existence of life on earth.
5. During photosynthesis, green plants take in carbon dioxide, water and light energy from the sun and in turn produce glucose and oxygen. Glucose is utilized by plants to carry out their general activities, and oxygen is liberated into the atmosphere.
6. It is due to photosynthesis only, the atmosphere of primitive earth got filled with oxygen and life began to sustain on earth as the end product of photosynthesis is oxygen.
7. Photosynthesis is a biochemical process as many enzymes [biological catalysts] are involved in the complex reactions of photosynthesis to form various intermediate chemical by-products.
8. Moreover, photosynthesis is a photochemical process because plants use light energy to break various chemical compounds in the intermediate reaction of photosynthesis.
9. The generalized photosynthesis reaction can be given as follows:
6CO2 + 12H2O + Light → C6H12O6 [Glucose] + 6O2 + 6H2O