Tests For Reactants And Products Of Photosynthesis.

Question 1

How to test for Starch:

Answer 1

• To do this you should first take the leaf you are about to test and, using tweezers, place it in a beaker of boiling water for a minute to kill it.
• Then place the leaf, using tweezers, into a boiling tube of boiling ethanol to remove all the chlorophyll. Use a water bath as ethanol is flammable.
• 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.

Question 2

How can you prove chlorophyll is necessary?

Answer 2

• Variegated leaves only have chlorophyll in some areas of the leaf. This means some areas of the leaf appear green, whereas others are white.
• To prove chlorophyll is needed you should place a destarched variegated plant in sunlight for several hours.
• You then test one of its leaves for the presence of starch.

Question 3

How can you prove light is needed for photosynthesis?

Answer 3

• Take a destarched plant (place it in darkness for 24 hours) and cover part of one of its leaves with black card or tin foil.
• Light cannot reach the covered area of the leaf.
• Place the plant in sunlight for several hours.
• Finally, remove the card from the leaf and test the leaf for the presence of starch

Question 4

How can you prove carbon dioxide is needed for photosynthesis?

Answer 4

• Take a destarched plant, 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,
• Then test one of its leaves for the presence of starch.

Question 5

How can you prove oxygen is given off during photosynthesis?

Answer 5

• Place an upturned test tube above an aguatic plant such as the pondweed Elodea.
• Put the apparatus in the light for a few hours 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.