Testing a Leaf For Starch

Question 1

What happens to glucose during photosynthesis?

Answer 1

It cannot be stored and is either used up or stored as insoluble starch

Question 2

What must you do to the plant before carrying out the experiment? Why?

Answer 2

It must be kept in the dark for 24-48 hours before starting the experiment because this will mean hat the plant will use up its store of starch

Question 3

What are the 5 steps needed to carry out the experiment?

Answer 3

1. The leaf is placed in a beaker of boiling water for 1 minute
2. The leaf is removed from the water and put into a boiling tube half full of ethanol
3. The boiling tube containing the leaf and ethanol is placed in the hot water for 10 minutes
4. The leaf is removed from the boiling tube and washed in the beaker of water
5. The leaf is placed on a white tile and covered in iodine

Question 4

Why is the leaf placed in boiling water?

Answer 4

It breaks down the cell membrane, making it easier for the iodine to enter the cell and to remove chlorophyll

Question 5

Why is the leaf placed in boiling ethanol?

Answer 5

The ethanol will dissolve the chlorophyll and removes the green colour from the leaf

Question 6

Why is the leaf washed?

Answer 6

It softens the leaf

Question 7

Why is the leaf covered in iodine?

Answer 7

The iodine reveals where the starch is because any parts containing starch will turn a blue-black colour