Question

3. How would you test the presence of starch in leaves?​

Answer 1

★The presence of starch in leaves can be tested by the Iodine test. When we remove chlorophyll from the leaf by boiling it in alcohol and then put two drops of iodine solution, it is colour change to blue indicates the presence of starch.

Answer 2

Answer:

Starch is a white, powdery substance consisting of glucose which is used by plants as food. The presence of starch in leaves is evidenced enough of the process of photosynthesis being carried out in leaves as the formation of starch necessitates photosynthesis.

Explanation:

Requirements:

Sample plants

Glass jar or beaker

Stove and saucepan

Iodine solution

Ethyl alcohol

Tweeze

Procedure:

Set up one plant on a sunny windowsill and another in a dark room for 24 hours

After 24 hours, fill a beaker with ethyl alcohol and place it in a saucepan full of water

Continue heating the pan until ethyl alcohol starts boiling and then take it off from the heat

With the help of tweezers, dip each of the leaves in hot water for a minute

Now, dip the leaves in the beaker holding ethyl alcohol for 120 seconds or till they change their color to almost white

Place each of them in a shallow dish

Cover these leaves with some drops of iodine solution and observe.

Observation:

Alcohol breaks down the chlorophyll and hot water kills the leaf. Hence, the leaf is no more green in color

When leaves are treated with iodine, one of them turns its colour to blue-black due to the presence of starch with iodine as an indicator. The other leaf turns its colour to reddish-brown

The leaf that was kept in light turns blue-black in colour indicating the leaf has been carrying out photosynthesis, producing starch.