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1.2

Minor Versionm

by Procheta Mallik

Introduction

Leaves are supposed to produce energy (food!). Here we test that theory by performing the starch test on it!

Video Overview

    • Alcohol is volatile, so make sure that the container it is in is closed if not using

    • Also, make sure the alcohol is not exposed to a naked flame

    • Be careful while boiling water and alcohol

    • Handle breakable materials like the test tube with care

  1. Boil about 500ml of water in a utensil Pluck any leaf from a tree/plant and place it in the boiling water and keep it there for 3 minutes.
    • Boil about 500ml of water in a utensil

    • Pluck any leaf from a tree/plant and place it in the boiling water and keep it there for 3 minutes.

  2. Take  5 ml of alcohol in a test tube Put the leaf in the test tube and dip the test tube in the boiling water Hold the test tube till the alcohol boils
    • Take 5 ml of alcohol in a test tube

    • Put the leaf in the test tube and dip the test tube in the boiling water

    • Hold the test tube till the alcohol boils

    • The alcohol will slowly turn green as the chlorophyll in the leaf dissolves in the alcohol

    • Keep shaking the test tube till the liquid gets darker and the leaf turns pale

  3. Take the leaf from the test tube with a tong and put it in the hot water and wait for 2 minutes Remove the leaf from the water with a tong and put 2 drops of iodine solution on the leaf and leave it for 2 minutes The leaf should turn a deep blue, confirming a positive test for starch!
    • Take the leaf from the test tube with a tong and put it in the hot water and wait for 2 minutes

    • Remove the leaf from the water with a tong and put 2 drops of iodine solution on the leaf and leave it for 2 minutes

    • The leaf should turn a deep blue, confirming a positive test for starch!

    • Why is it necessary to boil the leaf in alcohol?

    • Why does chlorophyll have to be removed before performing the starch test?

    • Do all leaves respond the same way for the starch test? Try the same experiment with leaves from different plants, or of different age/colour

    • The alcohol should be of good quality and high concentration

    • It is possible that up to 10 minutes are required to adequately remove the chlorophyll from the leaf while it is boiling in the alcohol

    • In this tactivity we have tested fresh green leaves for the presence of starch.

    • What do you think will happen if we test leaves which have been shed by trees for the presence of starch?

    • Will they also turn blue-black in colour on addition of iodine?

  4. Take a leaf which has been shed by the tree and has changed its colour from green to yellow. Place a metal container with water on a stove and boil the water Place the leaf in the boiling water and leave it to boil for 5-6 mins.
    • Take a leaf which has been shed by the tree and has changed its colour from green to yellow.

    • Place a metal container with water on a stove and boil the water

    • Place the leaf in the boiling water and leave it to boil for 5-6 mins.

    • Fish the leaf out of the water using a test tube holder or tongs and dry it by patting it.

  5. Tear the leaf and put a small bit of the leaf in the test tube and add some propanol to it. Grab the test tube using a test tube holder and place the test tube in boiling water, so that the propanol gets heated by the water.
    • Tear the leaf and put a small bit of the leaf in the test tube and add some propanol to it.

    • Grab the test tube using a test tube holder and place the test tube in boiling water, so that the propanol gets heated by the water.

    • Allow the propanol to boil for 5-6 mins.

    • Remove the leaf using a test tube holder and dry it again.

  6. Crumple the leaf lightly with your hand and then make it flat. This is to allow the iodine to get into the leaf and not just remain at the surface. Now add the iodine to the leaf and allow it to be for a minute or so. Pat the excess iodine off and look for any colour changes.
    • Crumple the leaf lightly with your hand and then make it flat. This is to allow the iodine to get into the leaf and not just remain at the surface.

    • Now add the iodine to the leaf and allow it to be for a minute or so.

    • Pat the excess iodine off and look for any colour changes.

  7. Cut out a piece of black paper and using tape, stick it to the top side of a leaf which is on a tree or plant. The leaf should be completely green with almost no hints of other colours. Allow the paper to be suck to the leaf for a week or more.
    • Cut out a piece of black paper and using tape, stick it to the top side of a leaf which is on a tree or plant.

    • The leaf should be completely green with almost no hints of other colours.

    • Allow the paper to be suck to the leaf for a week or more.

  8. After at least one week of sticking the black strip ,you can remove it. Pluck the leaf from the plant or tree.
    • After at least one week of sticking the black strip ,you can remove it.

    • Pluck the leaf from the plant or tree.

    • We will now test the leaf for starch

  9. Place the leaf in boiling water for 5-6 mins. Then remove the leaf from the water using a test tube holder or tongs. Allow  the leaf to dry completely.
    • Place the leaf in boiling water for 5-6 mins. Then remove the leaf from the water using a test tube holder or tongs.

    • Allow the leaf to dry completely.

    • Tear the leaf such that the region which the black strip was placed on is on one part of the leaf. You can discard the other part

  10. Place the part of the leaf in a test tube and add some propanol to the test tube. Hold the test tube using a test tube holder and place the test tube in boiling water. Make sure that the water and propanol do mot mix.
    • Place the part of the leaf in a test tube and add some propanol to the test tube.

    • Hold the test tube using a test tube holder and place the test tube in boiling water. Make sure that the water and propanol do mot mix.

    • After 5-6 mins, remove the test tube from the water bath

  11. Remove the leaf from the propanol and allow it to dry.
    • Remove the leaf from the propanol and allow it to dry.

    • Now add a few drops of iodine on the leaf and observe.

Finish Line

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