RP - Measuring Rate of Photosynthesis
- Created by: India.02
- Created on: 01-05-19 18:05
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- Required Practical - Measuring rate of photo-synthesis
- Method
- 1. A source of white light is placed at a specific distance from the pondweed
- 2. The pondweed is left to photo-synthesise for a set amount of time - as it does this, oxygen will be released and will collect in the capillary tube
- 3. At the end of the practical, a syringe is used to draw the gas bubble in a tube alongside a ruler - the length is measured
- This is proportional to the volume of oxygen produced
- 4. Any variables that can affect the results should be controlled - the temperature and the time that pondweed is left to photo-synthesise
- 5. Experiment is repeated twice with the source of light at the same distance and the mean volume of oxygen is calculated
- 6. Experiment is then repeated with the light source at different distances from the pondweed
- Apparatus
- Can be altered to measure the effect of temperature and carbon dioxide on the amount of oxygen produced
- Test tube can be put in a water bath at a set temperature
- A measured amount of sodium hydrogen-carbonate can be dissolved in the water - it gives off carbon dioxide
- Experiment is then repeated with different temperatures and a varied concentration of sodium hydrogen-carbonate
- Can be altered to measure the effect of temperature and carbon dioxide on the amount of oxygen produced
- Inverse Square Law
- When the lamp is moved away from the pondweed, the light intensity decreases
- Light intensity decreases in proportion to the square of the distance
- The law means that if you halve the distance, the light intensity will be 4x greater
- If you double the distance, the light intensity will be 4x smaller
- Light intensity can be measured with 1/d*2
- Method
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