6.5 testing leaves for starch

Question 1

what solution is used to test for starch?

Answer 1

iodine solution

Question 2

why doesn’t the leaf immediately turn blue-black when being tested for starch, unlike with other substances?

Answer 2

the starch is located inside the chloroplasts, thereby the iodine is unable to get through the cell membrane to reach the starch and react with it

Question 3

what makes the visibility of the starch blue-black indication difficult, aside from the cell membranes?

Answer 3

the colour mixture of the green (chlorophyll) leaves and the brown iodine solution

Question 4

what must be done to the leaf before being tested for starch?

Answer 4

it must be boiled in hot water to break down the cell membranes, then placed in alcohol to remove the chlorophyll

Question 5

what must be done before testing on leaves? why?

Answer 5

the plants that are being tested must be destarched; if the leaves were found to contain starch at the end of the investigation, it is uncertain whether they have been photosynthesizing as the starch may have been made before the investigation began

Question 6

how to destarch a plant?

Answer 6

the plant must be left in a dark cupboard for at least 24 hours so it does not photosynthesize, and it will use up its stores of starch while being isolated