Light intensity, light wavelength, temperature and availability of carbon dioxide

Equipment

• Pondweed
• Beaker
• Sodium hydrogen carbonate
• Aluminum foil
• Spatula
• Light filters (pieces of coloured cellophane)
• Photosynthometer
• Paperclip
• Bench lamp
• Ruler
• Thermometer
• Stop clock

Method

1. Place a piece of pondweed in a beaker of water.

2. Cover one side of the beaker with the aluminium foil to block out the light.

3. Cover the other side of the beaker with one of the light filters.

4. Add half a spatula of sodium hydrogencarbonate to the water to provide carbon dioxide.

5. Leave for 5 minutes.

6. Place the bench lamp a set distance from the beaker.

7. Set up the photosynthometer. Leave for 5 minutes.

8. Record the volume of gas produced during this time.

9. Replace the filter with another colour of filter and repeat the experiment.

Graph

• Plot a bar graph of colour of filter against volume of gas produced.

Conclusion

• Volume of gas produced is proportional to rate of photosynthesis.
• The greatest volume of gas will be produced when there is no filter used, because all

wavelengths of light can be absorbed.

• All filters will decrease volume of gas, but a green filter will decrease it the most

because chloroplasts don’t absorb much green light - it is mostly reflected, which is why

chloroplasts appear to be green.