What is the first practical in B1?
To test a leaf for the presence of starch.
What is the hypothesis for testing a leaf for starch?
Only the areas that contain chlorophyll
(the green parts) will photosynthesise and therefore test positive for starch, showing that chlorophyll is necessary for photosynthesis.
What is the risk assessment for testing a leaf for starch?
Do not use the Bunsen burner to heat the ethanol as it is very flammable.
What apparatus is needed for testing a leaf for starch?
Green plant, tongs, ethanol, funnel, kettle, white tile iodine solution.
What are the 11 steps in B1?
- Remove a leaf from the plant and place it in the beaker.
- Boil water in a kettle and pour the boiling water onto the leaf. Leave the leaf in the boiling water for 10 minutes; if it cools add in more boiling water. This will break down the cell walls.
- Use the tongs to remove the leaf from the boiling water.
- Place it into a test-tube.
- Use a funnel and carefully fill the test tube with enough ethanol to cover the leaf.
- Place the test-tube of ethanol with the leaf into the beaker of boiling water.
- If the water has cooled add more boiling water from the kettle.
- The ethanol will boil as it is heated to its boiling point of 78°C by the hot water. The boiling ethanol will dissolve the chlorophyll from the leaf.
- Remove the leaf from the ethanol and rinse it in the beaker of hot water. This will soften the leaf which will be brittle following boiling in ethanol.
- Place the leaf on a white tile.
- Drop iodine onto the leaf. Record the colour change.
What is the conclusion of the test for starch?
If starch is present: iodine changes to blue/black. If no starch is present: iodine remains orange/brown.
What is the second practical in B1?
To investigate the need for light in photosynthesis.
What is the hypothesis/ conclusion for investigating the need for light in photosynthesis?
Light is needed for photosynthesis to occur. When the plant photosynthesises, food will be made and stored in the leaf.
What are the steps for investigating the need for light in photosynthesis?
- De-starch the plant by placing it in a dark cupboard overnight.
- Test a leaf for starch.
- Leave the plant in sunlight or next to a lamp for a few hours.
- Test a leaf for starch.
What are the results for investigating the need for light in photosynthesis?
- The leaf from the plant when it was in darkness has no colour change when tested with iodine.
- The leaf from the plant after it was in sunlight has a colour change to blue/black when tested with iodine.
What is the third practical in B1?
To investigate the effect of light intensity on photosynthesis.
What is the risk assessment for investigating the effect of light intensity on photosynthesis?
Take care when handling wet glassware. The lamp may heat up so avoid touching potentially hot surfaces.
What are the 8 steps in investigating the effect of light intensity on photosynthesis?
- Place Elodea (Canadian pondweed) in a basin of water and place a funnel and measuring cylinder on top.
- Record the distance from the lamp to the plant.
- Bubbles of oxygen will be released from the pondweed as it is photosynthesising.
- Count the number of bubbles produced in one minute.
- Move the lamp further away from the plant.
- Repeat step 4.
- Move the lamp further away again.
- Compare the results.
What is the conclusion/ hypothesis of investigating the effect of light intensity on photosynthesis?
As the lamp moves further away from the plant the number of bubbles of oxygen produced every minute decreases.
Therefore the rate of photosynthesis will vary as the light intensity varies. The lower the light intensity the slower the rate of photosynthesis and vice versa.
