affect of light intensity on rate of photosynthesis

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Alex Tran

Biology experiment: photosynthesis

The effect of light intensity on Inelodea’s rate of photosynthesis

Aim:

Investigating the effect of increasing light intensity on rate of photosynthesis of Inelodea (water plant)

Light intensity is manipulated by changing the distance of the beakers from the lamp

Rate of photosynthesis is measured by looking at the pH change of NahCO3 solution. CO2 makes water more acidic. As CO2 is gradually used up during photosynthesis, the change in pH of the solution per time implicates the rate of photosynthesis.

Hypothesis:

The increase of light intensity will increase the rate of photosynthesis of Inelodea

        

Apparatus:

  • 5g of NaHCO3 (powder)
  • 5 beakers (100 ml)
  • Stirring rod
  • Balance
  • Universal pH indicators
  • 5 Inelodea plants (7 Cm long)
  • Distilled water
  • Lamp
  • 1 metre long ruler
  • Stop watch

Method:

  1. Fill each of the 5 beakers with 75 ml of distilled water
  2. Dissolve 1g of NaHCO3 (use balance to weight NaHCO3) in water to give CO2 supply
  3. Mark each beaker with letters A, B, C, D, and E
  4. Measure pH level of the 5 beakers before the experiment
  5. Place same size Inelodea (7 cm long) in to beaker A
  6. Place the beaker 20 cm apart from the lamp (using ruler to measure this distance)
  7. Measure the pH of the solution each 2, 4, 6 and 8 minutes
  8. The experiment is repeated for beakers B, C, D with distance 40 cm, 60 cm and 80 cm away from the lamp
  9. Beaker E is used as controlled, it is tested without the present of light from the lamp
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Independent variable:

Distance from the lamp (light intensity)

Dependent variable:

pH of the solution (rate of photosynthesis)

Controlled variables:  

  • Equal (75 ml) amount of water to be put in each beaker was ensure by the measuring marks on the beaker itself. This helps to have the same ratio between NaCOH3 and water in all 5 beakers  

  • Exactly 1g of NaHCO3 was weighted using balance then put into each beaker. This keeps the concentration of NaHCO3 (which supplies CO2) constant; therefore increase accuracy of the result. If NaHCO3 was put in different amount ...

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