Site author Richard Steane
The BioTopics website gives access to interactive resource material, developed to support the
learning and teaching of Biology at a variety of levels.
|
Site author Richard Steane
|
The BioTopics website gives access to interactive resource material, developed to support the
learning and teaching of Biology at a variety of levels.
|
|
Zebrina is a variegated plant similar to Tradescantia. This means that it has both green and white areas. Other variegated plants would probably work instead.
2 Draw it accurately, noting the colours of the various areas.
3 Drop it directly into boiling water in electric water bath. CARE!
Alternatively: use a beaker of water heated over a bunsen burner.
Leave it for 2 - 15 minutes.
4 Carefully extract leaf and place it into a wide test-tube. Shake it down to the bottom of the tube.
5 Just cover leaf with I.M.S. (ethanol).
6 Transfer tube containing leaf to other water bath, set at 80 °C.
Alternatively: use the beaker of water just heated BUT with the BUNSEN BURNER OFF.
CARE! Ethanol vapour is flammable.
Leave it for 15 - 30 minutes.
7 Tip away liquid.
8 Rinse leaf in (preferably hot) water.
9 Note appearance of leaf.
11 Add about 5 drops of iodine solution. Wait 10 minutes.
12 Note the colours of the various parts now.
13 Draw again, and answer the questions.
What are the green areas of the leaf composed of?
> cells containing chlorophyll
What are the white areas of the leaf composed of?
> cells containing NO chlorophyll
What was the purpose of boiling the leaf in water?
> to kill the cells and burst their chloroplasts
What was the purpose of the industrial methylated spirits?
> (as an organic solvent) to dissolve the chlorophyll
Why was pure ethanol not used?
> too expensive - Customs and Excise tax potable alcohol
Why was the second waterbath set at 80 °C?
> ethanol's boiling point is 78°C,it would boil away too quickly
What did the I.M.S. look like after the leaf had been in it for some time?
> green
What did the leaf look like after it had been in the I.M.S. for some time?
> not so green - +/- colourless
What does the iodine solution react with?
> starch
If the reaction is positive, what is the resulting colour?
> blue-black
If the reaction is negative, what is the resulting colour?
> orange
Look at the equation for photosynthesis again. What is the reason for using this test?
> glucose is turned into starch, which is easily tested for,
and being insoluble, it stays where it is!
What is the connection between the 2 colours on the leaf now and at the beginning?
| original colour | final colour |
|---|---|
| green | blue-black |
| white | orange |
Write a sentence explaining what you can conclude about factors required for photosynthesis from this experiment.
> chlorophyll is necessary to produce starch
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