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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: lucky
    Date: Feb 22, 2017

    i want to know what colour would appear if iodine was pured in a variegated leaf

    By: Vanessa
    Date: May 30, 2016

    Why do we have to test for starch and not glucose? Isn’t glucose the immediate product of photosynthesis and starch is glucose stringed together? So wouldn’t there be glucose in sites of photosynthesis?

    By: Dhanushnallanagula
    Date: May 27, 2016

    Why cant we add any another solution except iodine on petridish?

    By: Shaumbwa Tauno Natangwe
    Date: May 06, 2016

    what colors can be observed after 24 hours to the one left in sunlight and the one placed in dark? And what makes colors to change so?

    By: trevor
    Date: Jan 22, 2016

    by testing for starch we can get an idea of the health of the plant or tree before any visible indications occur that could show the tree is stressed. another way of testing is chlorophyll fluorescence. if the leaf turns reddish brown then no starch (food) is being produced by the leaf.

    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: linda nachalwe
    Date: Nov 03, 2015

    rather a question. do oranges or bananas have starch before ripening

    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?