Question

describe an experiment to show that chlorophyll is necessary for photosynthesis

Answer 1

First, take a plant with multi-colored leaves, and destarch it. Destarching it is putting it in a dark place or covering it with a dark cover for a day. Once all the starch is used, it is destarched.

Then, select one leaf from the plant, and mark the green areas (contains chlorophyll), and keep the plant in the sun for a few hours. Then, take the leaf and perform the test for starch.

Test for starch:

First, take a test tube with water, and boil the leaf. That weakens the cell membranes, and allows the other chemicals to react with the inner substances. Then, take some iodine solution in a test tube, and keep the leaf in the solution for a while. After that, you observe that only the marked turn bluish-black in color.

This is because, Iodine reacts with starch, and turns it bluish-black. This means, only the parts with chlorophyll had starch. Therefore, chlorophyll is essential for photosynthesis.

Answer 2

${ \underline{\boxed{ \bigstar {\bold {Aim:}}} }}$

• To show that chlorophyll is necessary for photosynthesis

${ \underline{\boxed {\bold {Materials \: Required:}}} }$

a coleus leaf, beaker, water, alcohol, iodine solution, test tube, tweezers, tripod stand, Bunsen burner, white tile

${ \underline{\boxed {\bold {Method:}}}}$

1. Pluck a leaf from a healthy plant and place it in a beaker of water. Boil the water for three minutes.
2. Take the leaf out carefully with tweezers and place it in a test tube of alcohol.
3. Place the test tube in the beaker of boiling water for 10 minutes.
4. Take the leaf out and wash it carefully inwater and place it on a white tile.
5. Place a few drops of iodine solution onthe leaf.

${ \underline{\boxed {\bold {Observations \: and \: conclusions:}}}}$

You will see that the alcohol removes the green colour from the leaf. The addition of iodine solution makes the parts of the leaf that were originally green turn blue-black. This shows that only the green parts of the leaf contain chlorophyll, and hence make starch.