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Practical: The Effect of Light on Gas Exchange in Plants (Edexcel IGCSE Biology)
Revision Note
Practical: The Effect of Light on Gas Exchange in Plants
Apparatus
- Boiling tubes
- Cotton wool
- Aluminium foil
- Gauze
- Rubber bungs
- Hydrogencarbonate indicator
- Leaves
Method
- Measure out 20 cm3 hydrogencarbonate indicator into 4 boiling tubes
- Put some cotton wool into each boiling tube
- Label the boiling tubes A-D and set them up as follows:
- Tube A - No leaf (control tube)
- Tube B - Place a leaf in the tube and leave in the light
- Tube C - Place a leaf in the tube and wrap it in aluminium foil to block out the light
- Tube D - Place a leaf in the tube and wrap it in gauze to allow partial light
- Put a bung into the top of each tube
- Leave all 4 tubes in the light for 30 minutes
Hydrogencarbonate indicator can be used to study gas exchange in different light conditions
Results
- After 30 minutes, we would expect the following results:
- Tube A - The control tube should remain an orange/red colour to show that the carbon dioxide is at atmospheric levels
- There has been no net movement
- Tube B - This tube was placed in the light with a leaf which is photosynthesising and respiring
- Because the rate of photosynthesis is greater than the rate of respiration, the hydrogencarbonate indicator will turn purple as there is less carbon dioxide than atmospheric levels
- Tube C - This tube had a leaf inside, but was wrapped in aluminium foil meaning that no sunlight could reach the leaf
- No light means that this leaf will not photosynthesise but will still be respiring, producing carbon dioxide. The indicator will turn yellow as carbon dioxide levels increase above atmospheric levels
- Tube D - This tube had a leaf inside and was wrapped in gauze allowing partial light
- This means that the rate of photosynthesis equals the rate of respiration so there was no net change in carbon dioxide levels and the indicator remained orange/red
Hydrogencarbonate indicator will change from orange/red to yellow with increasing carbon dioxide or purple with decreasing carbon dioxide
The Effect of Light on Net Gas Exchange in Plants Table
Applying CORMS evaluation to practical work
- When working with practical investigations, remember to consider your CORMS evaluation
CORMS evaluation
- In this investigation, your evaluation should look something like this:
- Change - We will change the availability of light for each boiling tube (not wrapped, wrapped in foil, wrapped in gauze)
- Organisms - The leaves should be from the same species/age of the plant, they should be approximately the same size
- Repeat - We will repeat the investigation several times to ensure our results are reliable
- Measurement 1 - We will observe the change in the hydrogen carbonate indicator
- Measurement 2 - after 30 minutes
- Same - We will control the volume of hydrogen carbonate indicator, the number of leaves, the temperature of the environment
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