STARCH TEST for PLANTS

STARCH TEST

 

CASE 1: STARCH IS PRODUCED DURING PHOTOSYNTHESIS

·       Take a green leaf fresh from the plant. And follow the steps shown.

Q. Why is the leaf boiled in water?

A. Because the process can soften the leaf, break down the cells.

 Q. Why is leaf then boiled in alcohol?

A. To decolorize the leaf to remove the chlorophyll.

 Q. Why is leaf put in hot water after being boiled in alcohol?

A. Since the leaf becomes brittle in alcohol, so it becomes softened in
hot water.

 Q. What color change can be observed if starch is present?

A. The leaf becomes blue-black when iodine is added to it.

 

CASE 2: CHLOROPHYLL IS NECESSARY FOR PHOTOSYNTHESIS

·       Take a leaf which is green and yellow(any color other than green).

·       Perform the starch test.

 

CASE 3: CO2 IS NECESSARY FOR PHOTOSYNTHESIS

 ·       Take a green colored leaf.

·      Cover one leaf with a polythene containing water and cover other other leaf containing Potassium Hydroxide. 

·       Keep it in sunlight for some time.

·      Take both the leaves and perform the starch test.

 

Q. Why is potassium hydroxide solution put in one of the flask?

A. To absorb all CO₂ in the flask B. 

Q. What happens to each leaf after carrying out the starch experiment?

A. The leaf in flask A changes to blue-black while the leaf in Flask B
remains same.

 

CASE 4: O₂ IS PRODUCED DURING PHOTOSYNTHESIS

·       Take a green water submerged plant say Hydrilla. 

·       Keep it in sunlight for some time. 

·      You can see the bubbles of gas coming out from the funnel.

 CONCLUSION:

These bubbles are of O2 that is produced during photosynthesis and since Oxygen is lighter than water it travels up.

 

CASE 5: SUNLIGHT IS NECESSARY FOR PHOTOSYNTHESIS

·       Take a green leaf and cover a strip of black paper on a part of leaf.

·      Keep it in sunlight for some time.

·       Do the starch test after some time.

 

 

CONCLUSION:

The part of the leaf that was covered with black paper, did not receive the sunlight and so did not carry out photosynthesis. So, there was no starch present in this area. Hence this area failed the starch test.

 

 WHAT HAPPENS IF LEAVES OF A GREEN PLANT ARE COATED WITH OIL?

The gaseous exchange is done through the stomata present on the leaf surface. These tiny pores get blocked by oily layer. It is like closing our nose and mouth tightly. Since the intake of Carbon Di oxide is reduced and maybe totally blocked, so leaf will not be able to make the food and may ultimately die.