Unit 6 Experiments Flashcards
How can you determine whether or not chlorophyll is necessary for photosynthesis?
Use a plant with a variegated leaf on it. Destarch the leaf then expose it to sunlight for a few hours. When testing for starch the green areas with chlorophyll which produces starch should turn blue and the white areas without chlorophyll should turn brown.
What is a variegated leaf?
A variegated leaf is a leaf that only has patches of chlorophyll in it. The areas without chlorophyll will usually be white and the areas with chlorophyll should be green.
How can you determine if light is needed for photosynthesis to occur?
Get a leaf still attached to a plant, then wrap aluminium foil around the leaf that has a hole in it. After 4-6 hours of daylight remove the foil and test for starch. If the areas that were covered turn brown indicating a lack of starch and the areas not covered turn blue indicating the presence starch. We could argue that light is needed for photosynthesis.
How can you determine if carbon dioxide is needed for photosynthesis to occur?
Water two destarched potted plants and enclose them in polythene bags. In one pot put some soda lime to absorb the carbon dioxide and in another put some sodium hydrogencarbonate solution to produce carbon dioxide. Leave the plants in the light for several hours then test a leaf from each plant for starch. If the leaf with sodium hydrogencarbonate turns blue and the one with soda lime turns brown, this must mean that carbon dioxide is required for photosynthesis.
How can you determine if gas exchange is affected by being kept in the light and in the dark?
- Fill three boiling tubes about two-thirds of the way with hydrogencarbonate indicator solution.
- Place Canadian pondweed in two of the boiling tubes.
- Seal the three tubes with stoppers
- Leave one of the test tubes with pondweed in the light and the one without pondweed also in the light.
- Place the last boiling tube in darkness.
- After 24 hours note the colours of the hydrogencarbonate solution.
What colours will indicate if gas exchange is affected by light and darkness?
The boiling tube left in the light without pondweed should not change colour (it should be pink/red). The boiling tube with pondweed left in the light should be yellow, this indicates that carbon dioxide was absorbed, and the boiling tube left in darkness should be purple, this indicates that carbon dioxide was released (from respiration).
