B1.4.2 - Photosynthesis experiments

Question 1

How can you prove chlorophyll is needed for photosynthesis?

Answer 1

Variegated leaves only have chlorophyll in some areas of the leaf. This will appear green. To prove chlorophyll is needed you should place a distracted variegated plants in sunlight for several hours. You then test one of the leaves for starch

Question 2

How can you prove light is needed for photosynthesis?

Answer 2

You take a destarched plant and cover part of one of its leaves with black card or tin foil so light cannot reach it.
You then palace it in sunlight for several hours. After that you remove the card from the leaf and test the leaf for presence of starch

Question 3

How can you prove carbon dioxide is needed for photosynthesis?

Answer 3

You take a destarched plants and place it inside a polythene bag. Before you seal the bag add a pot of soda lime. This is a chemical that absorbs carbon dioxide and water vapour.
Place the plant in sunlight for several hours, before testing one of its leaves for the presence of starch

Question 4

How can you prove oxygen is given off during photosynthesis?

Answer 4

Place an upturned test tube above an aquatic plants such as pondweed. Put the apparatus in the light for maximum photosynthesis.
When you have collected a full tube of gas, place a glowing splint inside the tube. It will relight because of the oxygen present

Question 5

How can you test for starch?

Answer 5

You boil a leaf in hot water
The place the leaf into a boiling tube of ethanol to remove all the chlorophyll
Then wash the leaf with water to remove the ethanol and soften the leaf and spread it out on a white tile
Add a few drops of iodine solution onto the leaf
If starch is present the iodine will turn from yellow-brown to blue-black