Testing for Starch in Plants


Plants make their food through the process of photosynthesis. This process uses light from the sun and chlorophyll from the leaves. The plant uses up carbon dioxide from the surrounding environment. Oxygen is its byproduct. The resulting starch stores glucose, which is the plant’s food. Checking for starch in the leaves is proof that there is photosynthesis.

What you need:

  • Tweezers
  • Two plants
  • Iodine solution
  • Glass jar or beaker
  • Ethyl alcohol
  • Saucepan on a stove

How you do it:

  1. Take one plant and place it in a dark room for a day. Position the other plant on a windowsill that has plenty of sun for a day.
  2. Fill your jar or beaker with ethyl alcohol.
  3. Place the jar or beaker in a water-filled saucepan.
  4. Heat the water bath until the ethyl alcohol starts boiling.
  5. Take the pan off the heat.
  6. Dip the leaves of the plants in the hot water for a minute using your tweezers.
  7. Drop the leaves into the container of ethyl alcohol until they turn almost whitish.
  8. Place the leaves in a shallow dish.
  9. Use the iodine solution to cover the leaves. Observe carefully.

What took place:

Alcohol broke down the chlorophyll in the leaves. The hot water killed the leaves. These two ingredients took the chlorophyll from the leaves. Once you put iodine on the leaves, they turn bluish-black. This shows the presence of starch in the leaves of the plant on the windowsill. The leaf from the plant in the dark room will appear reddish brown.

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