Tests For Reactants And Products Of Photosynthesis. Flashcards
How to test for Starch:
• 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.
How can you prove chlorophyll is necessary?
• 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.
How can you prove light is needed for photosynthesis?
• 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
How can you prove carbon dioxide is needed for photosynthesis?
• 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.
How can you prove oxygen is given off during photosynthesis?
• 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.
The Pondweed Experiment (Elodea Experiment):
Steps:
Aim: To measure the rate of photosynthesis by observing the oxygen produced by the pondweed.
1. Place a piece of pondweed (e.g., Elodea) into a beaker filled with water.
2. Add a small amount of sodium bicarbonate (baking soda) to the water to provide carbon dioxide for the plant.
3. Position a lamp at a set distance from the beaker to provide light for the photosynthesis process.
4. Allow the plant to acclimatize to the light for a few minutes.
5. Observe and count the number of oxygen bubbles produced by the pondweed over a set period (e.g., 5 or 10 minutes). Oxygen is produced as the plant carries out photosynthesis.
6. Repeat the experiment with different light intensities (by moving the lamp closer or further away) or other variables, such as temperature, to investigate their effect on the rate of photosynthesis.
The Leaf Disc Experiment
Aim: To measure photosynthesis by observing the rate at which leaf discs float due to oxygen production.
Steps:
1. Use a hole puncher to cut small discs from a healthy leaf.
2. Place the leaf discs in a syringe with a solution of water and sodium bicarbonate (to provide carbon dioxide).
3. Pull the plunger of the syringe to create a vacuum. This causes the air in the leaf discs to be removed, making them sink to the bottom of the syringe.
4. Place the syringe under a light source (like a lamp).
5. Over time, as photosynthesis occurs, oxygen is produced and replaces the air in the leaf discs. This makes the leaf discs float to the top of the syringe.
6. Measure the time it takes for the leaf discs to float to the top. The quicker they rise, the faster the rate of photosynthesis.
7. Repeat the experiment by altering variables such as light intensity or temperature to see how they affect the rate of photosynthesis.
