Question

0. 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.

Answer 1

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Answer 2

The presence of starch is determined with the help of the iodine test. The starch turns into an intense blue-black color by reacting with an aqueous solution of the triiodide anion. The color develops due to the production of an intermolecular charge-transfer complex.

In the given case, just before the starch test pale yellow color is observed, while after the starch test, blue-black color formation takes place.  

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

In the presence of sunlight, the above reaction takes place. Oxygen is obtained from water, as dissociation of the water molecule leads to the production of hydrogen, and oxygen that is a by-product.