B1.4.2 - Photosynthesis Experiments

Question 1

What does testing for starch help with?

Answer 1

With this you can show that light, chlorophyll and carbon dioxide are all essential for photosynthesis

Question 2

Explain the experiment for testing for starch

Answer 2

1) Using forceps, place leaf in beaker of boiling water for a minute
2) Then place leaf in boiling tube of boiling ethanol
3) Wash leaf with water, removing ethanol and softening leaf
4) Place onto a white tile
5) Add few drops of iodine solution
6) If starch is present, the iodine will turn from yellow brown to blue black

Question 3

Why do you boil the leaf before testing?

Answer 3

The water kills the leaf, preventing further photosynthesis

Question 4

What does a positive test indicate for starch?

Answer 4

The iodine is now blue black

Question 5

How do you prove chlorophyll is needed?

Answer 5

Place a de starched variegated plant in sunlight for several hours
Then test one leaf for starch

Question 6

How can you prove light is needed?

Answer 6

Cover part of a de starched plant with foil or black card
This will prevent light from reaching that part
Leave it in sunlight for several hours
Then test it for starch
Ideally, the part that WASN’T covered would show a presence in starch and the part that WAS wouldn’t

Question 7

How can you prove carbon dioxide is needed?

Answer 7

Place a de starched plant inside a polythene bag
Before sealing, add a pot of soda lime
Soda lime is a chemical that absorbs carbon dioxide and water vapour
Leave in sunlight for several hours, then test for starch

Question 8

How can you prove oxygen is given off during photosynthesis?

Answer 8

Place an upturned test tube above an aquatic plant
Put apparatus in light for maximum photosynthesis
When the tube is full of gas, place a glowing splint inside
It should relight due to oxygen present