10: Investigate the effects of different wavelengths of light on the rate of photosynthesis.

Question 1

Name the photosynthetic pigments in chloroplasts.

Answer 1

chlorophyll alpha, chlorophyll beta, carotene

Question 2

Why do chloroplasts contain different photosynthetic pigments?

Answer 2

Each pigment absorbs different wavelengths of light, therefore light absorption is maximised.

Question 3

How can the rate of photosynthesis be measured?

Answer 3

Measuring the volume of gas produced.

This gas is assumed to be oxygen; carbon dioxide from respiration is ignored

Question 4

Method:

Answer 4

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 hydrogen carbonate 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 five minutes.
8. Record the volume of gas produced during this time.
9. Replace the filter with another colour of filter and repeat the experiment.

Question 5

Risk

Answer 5

Biohazard: contamination
-use disinfectant, wash hands with soap after handling.

Sodium hydrogen carbonate: low hazard

• avoid inhalation/ contact with eyes
• wear eye protection, avoid contact with skin

Lamps
-do not look directly at lamp

Question 6

Conclusion:

Answer 6

• 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 the 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.