h asked in 科學及數學生物學 · 1 decade ago

why should we kill the leaf before iodine test?

Q1:why should we kill the leaf before iodine test?can we just put it into the alcohol then cover it with iodine solution?

Q2: The leaf becomes brittle after putting into alcohol so we should dip it into hot water to soften it. But why should we soften it?

2 Answers

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  • 1 decade ago
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    Q1: We need to boil the leaf to kill the plant cells so that iodine can enter.

    Q2: We use alcohol to kill the chlorophyll in the leaf to test for starch. Hot water is needed to wash away the alcohol.

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    2007-01-20 17:34:39 補充:

    other answer......Putting the leaf in alcohol before having the iodine test is to make an easier observation, for the green colour of chlorophyll in leaf will make the observation (If there is starch, iodine will change from brown to dark blue) more difficult.

    2007-01-20 17:34:51 補充:

    Alcohol can dissolve and destroy the cell membrane so that the chloroplast will be exposed to the alcohol and dissolved in it. After putting the leaf into a tube of alcohol in a hot water bath, you will see the solution in the tube become green.

    2007-01-20 17:35:10 補充:

    The reason of putting the leaf into a tube of alcohol in a hot water bath is to speed up the destruction of the cell wall. Putting the leaf in a tube of alcohol without hot water bath to remove chloroplast in leaf is time-consuming.

    Source(s): 本人
  • 1 decade ago

    Q1: In case there are some bacteria affect the iodine test.Also, a high temperature can help to breakdown cell walls ,which means the starch inside the plant cells can more easily be released.Moreover, this step can even help the plant cells to release its chloroplast, hence the colour of the iodine-starch complexes are clearer.

    We can't just put it into the alcohol then cover it with iodine solution, because the starch inside the cells haven't came out.There will be not affected to the iodine solution.

    Q2: To clear the alcohol that covering the leaf.

    The moist surface area provides a media for iodine to react.

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