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Photosynthesis Lab

Free essay example:

Yakir Starosta

IB Bio 12

Photosynthesis Lab

Research Question: Investigate the rate of photosynthesis of an elodea plant by measuring the amount of oxygen that is produced by it.


Independent Variable:

The Independent variables are the different colors of cellophane paper that are wrapped around the 15 test tubes. The 5 different colors are green, blue, red, yellow and one without any cellophane paper.

Dependent Variable:

The dependent variable is the elodea plant as we are measuring the amount of oxygen that is produced by it through photosynthesis.

Controlled Variables:

  • Amount of water that is put into the test tubes – (This is going to be controlled by carefully filling up the whole test tube and carefully flipping it into the beaker with the water).
  • Amount of water in Beakers – (This is going to be controlled as the beakers are measurement beakers and I can determine when I have 200ml of water by looking at the side of the beaker)
  • Amount of cellophane paper around test tubes – (This is going to be controlled by using the same amount of cellophane paper to wrap around each test tube {12.2 X 7.4 cm each} )
  • The time that the test tubes are kept under the light – (I am going to control this by keeping the test tubes under the light for 8 days)
  • The length of the Elodea plant – (I am going to control this by using a ruler to measure out 11.3 cm of the Elodea plant for each trial)


  • 15 test tubes (15ml each)
  • Ruler
  • Scissors
  • Water
  • 5 beakers (250ml)
  • Elodea plant (15 pieces of 11.3cm each)
  • Masking tape
  • Light and light bulb of 100 watt
  • Cellophane paper (15 pieces of 12.2 X 7.4cm each)


Method (procedure):

  1. I gathered all my apparatus
  2. I then measured the test tubes and figured out home much cellophane paper I need in order to wrap each test tube (12.2 x  7.4 cm for each one)
  3. I took 4  rolls of cellophane paper (Blue, Green, Yellow and Red)
  4. From each different cellophane color I cut 3 pieces of 12.2 X 7.4cm
  5. I then wrapped all the 12 pieces of cellophane around 12 different test tubes and used masking tape to stick keep it on the test tube.
  6.  I had 3 other test tubes that I did not wrap any colored cellophane around them; I left them as they are.
  7. I had 3 trials for each color of cellophane
  8. I then took an elodea plant and cut 15 pieces of 11.3cm.  I did this by using scissors and a ruler.
  9. I took 5 beakers (250ml) and put 200ml in each.
  10. I then took the elodea pieces and put them in each test tube.
  11.  After putting each piece, I filled the test tube with water till it was full and put it in a beaker upside down without letting the water go out.
  12. I repeated this step for all my test tubes.
  13. I then put all the beakers with the test tubes under a light and left them there for 8 days.
  14.  8 days later I measured my results.
  15.  I used a ruler to measure all the oxygen that was produced in each test tube.
  16. I then measure a test tube (12.2 cm)
  17.  I then took the amount of water that can be put into the test tube and divided it be length of the test tube
  18.  I used the result of this and multiplied it by each one of my results from the trials and came up with how many milliliters of oxygen were produced.

Different color of cellophane paper

Trials  ± 0.1cm

Avg. of trials ± 0.1cm

Trial 1

Trial 2

Trial 3





















no cellophane paper





Table representing the amount of oxygen that was produced in each trial by the Elodea plant and the average of the trials of each different color of cellophane paper that was used

Table representing the conversion of the amount of oxygen that was produced by the Elodea plant from centimeters to milliliters

Different colors of cellophane paper

Avg. of Trials

Convert into ml ± 0.1













No cellophane paper





Average: The sum of all the trials divided by the number of trials

The conversion of cm to ml: 15/12=1.5, the averages multiplied by 1.5

(The amount of ml that the test tube can contain divided by the length of it)


        Photosynthesis is the process by which carbohydrates are synthesized from carbon dioxide and water using light as an energy source.  Most forms of photosynthesis release oxygen as a byproduct.[1]  This is the process that we used in our lab, the elodea plant synthesized from carbon dioxide and water using light as an energy source and releasing oxygen into the test tube as a byproduct.   According to my results and the data that I collected, it is visible that when the Elodea plant is wrapped with a yellow or red cellophane paper then a lot of oxygen is produced as a byproduct, when there it is not wrapped with any colored cellophane paper then there is a bit of oxygen produced and when it is wrapped with blue or green cellophane paper then barely any oxygen is produced as a byproduct.  I researched about Photosynthesis and came up with the scientific theory that violet/blue light has the highest level of absorbance, orange/red light has the second highest level of absorbance and yellow/green has the lowest level of absorbance.  The results of my lab did not match the scientific theory red and yellow had the highest level of absorption due to the amount of oxygen that was produced, yellow had the second highest and green and no color had the lowest.  The only color that followed the scientific theory was the green color as it had the lowest level of absorbance.  There is no scientific theory for the trials that did not have any color.  I used the uncertainty of ±0.1 in my results but the uncertainty is too small in order to make any change relating to the scientific theory.  I had an error in my calculation when I converted the results that I had in centimeters to milliliters. Instead of multiplying the results by 1.25 I multiplied them by 1.5 because 15/12.2 = 1.25.   This wrong calculation affected my results as they were not accurate but it did not affect the graph and the different rates of absorption that the different colors had.  Overall, my data and results did not follow the scientific theory; therefore there must have been errors throughout the lab.  I probably did not control all the controlled variables well enough and keep them constant.  I added an uncertainty (±0.1) due to the fact that I had to control variables.  The systematic error that I had such as the wrong placement of my results on the graph affected my conclusion as they did not reflect the scientific theory.  So overall, my conclusion is that, if there are no errors in the lab and the results are accurate and precise then the data on the graph is supposed to follow the trend of the scientific theory which is, violet/blue light has the highest level of absorbance, orange/red light has the second highest level of absorbance and yellow/green has the lowest level of absorbance.




[1] http://www.answers.com/topic/photosynthesis

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