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Home / Science projects / Photosynthesis: Testing for Starch
  • Photosynthesis: Testing for Starch

    Photosynthesis: Testing for Starch

    Any extra food a plant makes through photosynthesis is stored in its tissue as starch. Testing a leaf for starch is one way to test whether it has been performing photosynthesis. (Adult supervision required.)

    What You Need:

    What You Do:

    1. Put one of the plants in the dark for 24 hours; leave the other one on a windowsill.
    2. After 24 hours, put some ethyl alcohol in a beaker and place that in a saucepan full of water. Heat the pan until the ethyl alcohol begins to boil. Remove from the heat.
    3. Use tweezers to dip each of the leaves in the hot water for 60 seconds. Then place them in the beaker of ethyl alcohol for two minutes or until they turn almost white. Set them each in a shallow dish.
    4. Cover the leaves with some iodine solution and watch.

    What Happened:

    The hot water kills the leaf and the alcohol breaks down the chlorophyll, taking the green color out of the leaf. When you put iodine on the leaves, one of them will turn blue-black and the other will be a reddish-brown. Iodine is an indicator that turns blue-black in the presence of starch. The leaf that was in the light turns blue-black, which demonstrates that the leaf has been performing photosynthesis and producing starch.

    Try the test again with a variegated leaf (one with both green and white) that has been in the sunlight. A leaf needs chlorophyll to perform photosynthesis — based on that information, where on the variegated leaf do you think you would find starch?

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By: TeeKay
Date: Jan 25, 2015

thank you for the help. My Biology assignment was on point

By: Serena
Date: Jan 17, 2015

How much alcohol do i pour inside the beaker? The whole thing?

By: tiffeny
Date: Jan 15, 2015

why does the alcohol turn green?

By: xzavia simon
Date: Jan 14, 2015

This really help with my biology assignment thanks

By: thanaa
Date: Jan 08, 2015

i think we will find starch on the green region of the variegated leaf

By: shaima
Date: Jan 07, 2015

nice experiment, i will try it at home

By: jehoshebeth ferdinband
Date: Jan 01, 2015

great help with the iodine being an indicator

By: tricia phillips
Date: Nov 24, 2014

where on the leaf did it turn blueblack? and why was the plant destarched prior to the experiment?

By: Brayoh
Date: Nov 09, 2014

Wow , an excellent explanation

By: D
Date: Nov 06, 2014

I know a way to see if food has starch!