Factors Affecting the Rate of Photosynthesis Lab

Authors Avatar

Kyle Hovey

Factors Affecting the Rate of Photosynthesis

Research Question: How does light intensity affect the number of bubbles produced by a branch of elodea in 400mL of sodium hydrogen carbonate (4g) solution in 30 seconds?

Variables:

  • Independent: light intensity
  • Dependent: number of bubbles produced in a 30-second period
  • Control: availability/amount of water (I will assume that the elodea has a consistent volume of water available at all points on its surface), type of plant (I will be using a piece of elodea), size of elodea (the sample of elodea is a branch from a larger piece of elodea, about the same size as other branches from it), availability of carbon dioxide (the elodea is in a 400mL solution of 4g of sodium hydrogen carbonate), mass of plant (I will be using one piece of elodea for all my trials), type/color of light source (I will be using a single 40W bulb that emits what I will assume to be white light for all of my tests), angle/position of light (I am going to let the bulb rest in one spot, and for each test I do, I will move the beaker containing elodea and sodium hydrogen carbonate solution closer to or further away from the light source), amount of outside light (the room’s lights will stay on, and I will include this in the measurement of light using a lux meter), time allowed for plant to photosynthesize between trials (I will let the plant sit for 1 minute under the intensity of the light I am testing and then commence counting bubbles every 30 seconds for 3 consecutive trials)

Hypothesis: I expect that, at low light intensities, the rate of photosynthesis will be slower than the rate of photosynthesis at higher light intensities because the chlorophyll in the elodea is absorbing less light, so fewer bubbles will be produced, compared to higher intensities. As a result, increased numbers of photosynthetic reactions will occur (up to a certain level, at which point all chlorophyll are working at maximum efficiency).

Graph to Estimate the Relationship Between Light Intensity and the Number of Bubbles Produced in a 30-Second Period in a 400mL Sodium Hydrogen Carbonate (5g) Solution

Method:

  1. Pour 4g of sodium hydrogen carbonate into a beaker and dissolve in 400mL of distilled water to make a solution
  2. Snip the tip of the stem and the top of the branch of a leafy branch of elodea
  3. Place the elodea in the solution so that the stem points upward towards the opening of the beaker
  4. Put a glass funnel into the beaker (wide end down, tube pointing upward) so that it helps to keep the elodea at the bottom of the solution and angles the stem upward
  5. Turn on a 40W bulb and rest it on a flat surface so that illuminates horizontally
  6. Using a lux meter, locate the spot that the beaker needs to be placed so that it is shined on with 13 lux and let the beaker sit for 1 minute
  7. Record the number of bubbles the elodea produces every 30 seconds for 1 minute and 30 seconds
  8. Using a lux meter, locate the spot that the beaker needs to be placed so that it is shined on with 135 lux and let the beaker sit for 1 minute
  9. Record the number of bubbles the elodea produces every 30 seconds for 1 minute and 30 seconds
  10. Using a lux meter, locate the spot that the beaker needs to be placed so that it is shined on with 245 lux and let the beaker sit for 1 minute
  11. Record the number of bubbles the elodea produces every 30 seconds for 1 minute and 30 seconds
  12. Using a lux meter, locate the spot that the beaker needs to be placed so that it is shined on with 420 lux and let the beaker sit for 1 minute
  13. Record the number of bubbles the elodea produces every 30 seconds for 1 minute and 30 seconds
  14. Using a lux meter, locate the spot that the beaker needs to be placed so that it is shined on with 640 lux and let the beaker sit for 1 minute
  15. Record the number of bubbles the elodea produces every 30 seconds for 1 minute and 30 seconds
Join now!

Data Table:

Graph to Show the Relationship Between Light Intensity (lux) and the Number of Bubbles Produced in a 30-Second Period in a 400mL Sodium Hydrogen Carbonate (5g) Solution

Conclusion:

        The results I obtained obviously support my hypothesis that at low light intensities, the rate of photosynthesis is slower than the rate of photosynthesis at higher light intensities, and is very well demonstrated by the above graph. The chlorophyll absorb more light when under higher light intensities, thus allowing increased reaction rates. Oxygen gas was produced, which I counted as bubbles were produced and floated to ...

This is a preview of the whole essay