Rate of Photosynthesis

The purpose of this lab is to investigate the influence of light intensity on the rate of photosynthesis.

Background

1. Where in the plant cell does photosynthesis occur?

2. What is the purpose of photosynthesis?

3. Write the general equations for photosynthesis. Identify reactants and products of the reaction.

4. What factors may influence the rate of photosynthesis?

Hypothesis

Identify the independent and dependent variables in this lab.

Write a hypothesis for this experiment using the “if…then…” format.

Materials

Large test tube / sodium bicarbonate solution / Lamp / Thermometer / Large stir rod
Plant sample / Watch with a seconds hand / Meter stick / Heat sink

Procedure

  1. Obtain a plant sample.
  2. Place theplant samplein a large test tube, Use the large stir rod to move the plant into test tube, be sure to not puncture the plant sample.
  3. Completely cover the plant samplewith sodium bicarbonate solution.
  4. Construct the set-up demonstrated in class. The initial set-up should be at the furthest distance you are testing.
  5. Turn on the lamp and wait five minutes. This will allow the system to reach equilibrium.
  6. Observe and record the number of bubbles generated in 5 min.
  7. Decrease the distance of the lamp from the large test tube by 20cm.
  8. Repeat steps 4 and 5 for a second distance.
  9. Decrease the distance of the lamp from the large test tube by 20cm.
  10. Repeat steps 4 and 5 for a third distance.
  11. Clean-up lab area and return supplies.
  12. Add your group’s data to the board and complete your data table.

Data

Distance from Lamp / 10cm / 20cm / 30cm / 40cm / 50cm / 60cm
Bubbles Observed : Group Data
Bubbles Observed : Average of class data
Light Intensity

Graph

  1. Calculate the light intensity at each distance using the following formula:

Light Intensity = 1

Distance from lamp (cm)

  1. Graphthe light intensity on the x-axis and the average number of bubbles for each distance on the y-axis.

Analysis Questions

  1. Why did we use sodium bicarbonate solution (NaHCO3) in the lab? Hint: What does the plant need to photosynthesize?
  1. What gas was the plant producing in the lab?
  1. What is the relationship between light intensity and distance from the light source?
  1. Using your data table, how does the distance from lamp affect the rate of photosynthesis?
  1. Using your graph, how does the light intensity affect the rate of photosynthesis?
  1. Identify one other factor or variable that could influence the rate of photosynthesis? Describe an experiment to test the factor you identify.

Conclusion

Refer to your experiment outcome, your data, to explain whether your hypothesis is supported or refuted. If your results deviate from the expected outcome, please explain how this may have happened.