Starch Experiment

Question 1

How would you test a leaf for starch?

Answer 1

1. Remove leaf from plant
2. Place leaf in boiling water for at least 30 seconds. This kills the leaf and stops further reactions
3. Add leaf to boiling tube of ethanol and place in water
   bath. Bunsen MUST be switched OFF- ethanol is FLAMMABLE.
4. This removes chlorophyll from the leaf – leaf changes
   colour from green → white
5. Dip leaf in boiling water again
6. Add iodine solution to leaf
7. If starch is present the iodine will change from a red/brown
   colour to a blue/black colour.

Question 2

How would a normal leaf look when tested for starch? Why?

Answer 2

Blue/Black all over, as this type of plant photosynthesises all over.

Question 3

How would a variegated leaf when tested for starch? Why?

Answer 3

Blue/Black where the plant was originally green, but on the outside, where no chlorophyll is present, orange/brown. No Chlorophyll = No Starch.

Question 4

If a leaf is placed in a cupboard of 48 hours, what will it look like when tested for starch. Why?

Answer 4

The leaf would be orange/brown all over, because there is no sunlight in a cupboard, the plant cannot photosynthesise, which means no glucose can be produced, and then no starch.

Question 5

If a black strip of paper is attached to a leaf, 48 hours later, will it produce starch in the areas that it was blocked? True or False?

Answer 5

False.