How would you test the presence of starch in leaves?

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.

Requirements:

  • Sample plants
  • Glass jar or beaker
  • Stove and saucepan
  • Iodine solution
  • Ethyl alcohol
  • Tweezer

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

34 Comments

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