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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:


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    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: Ann
Date: Dec 30, 2015

We test the leaf for the existence of starch because starch ( glucose) is one of the products of photosynthesis. If starch ( one of the products of photosynthesis is present in the plant, it means that the plant underwent the process of photosynthesis.

By: just answering
Date: Dec 14, 2015

maybe to test if the food is edible.u can test for bananas too i guess cause itz edible…and has starch.

By: Confused
Date: Sep 20, 2015

Why do we test for starch and not for (for example) bananas or something else?

Furthermore, I know it would be real stupid testing for bananas but it was an example because I really don’t know why we test for starch; please help?!

By: albertina
Date: Sep 11, 2015

quiet clear….but so the plant can just kept in the dark for 24 hours????what if I extend the time to 48 hours?

By: Jannie
Date: Jul 24, 2015

What if it turns reddish-brown? What does it indicate?

By: Oscar motise
Date: Jul 22, 2015

You put the plant in the dark for 24 hours and leave the other one in a windowsill

By: lawal muhammad
Date: Jul 08, 2015

yes the existance of black_blue colouration indicate the presence of starch in a green plant

By: Abdulainallo
Date: Jul 02, 2015

Can leaf be a medicine?

By: Mike nyondo
Date: Jun 17, 2015

Please help how can l test starch in a cassava,

[HST adds:  Try this article on testing for starch in food.  http://www.hometrainingtools.com/a/thanksgiving-dinner-science-projects  Hope this helps!]

By: Snenhlanhla
Date: Jun 07, 2015

What is the hypothesis for this experiement?