Yahoo 知識+ 將於 2021 年 5 月 4 日 (美國東岸時間) 停止服務,而 Yahoo 知識+ 網站現已轉為僅限瀏覽模式。其他 Yahoo 資產或服務,或你的 Yahoo 帳戶將不會有任何變更。你可以在此服務中心網頁進一步了解 Yahoo 知識+ 停止服務的事宜,以及了解如何下載你的資料。

h 發問於 科學及數學生物學 · 1 十年前

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 個解答

評分
  • 1 十年前
    最愛解答

    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.

    希望幫到你...!

    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.

    資料來源: 本人
  • 1 十年前

    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.

還有問題嗎?立即提問即可得到解答。