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Investigation 5: Photosynthesis

AP Biology, Cellular Processes: Energy and Communication

Wayne Chang

on 10 April 2016

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Transcript of Investigation 5: Photosynthesis

Photosynthesis Lab
Number of Disks Risen/ Time
Wayne Chang
Andrew Jeng
Austin Wertz

Thanks For Listening
• 2 plastic syringes
• Living leaves (the one outside of bio class room)
• Hole punch
• 5 clear plastic cups
• Timer
• Light source (2 lamps)
• Cardboard box
• Tin foil
• Soap solution
• Distilled water
• Prepare 5 cups and on all of them measured a 3 cm mark and add water up to the mark and add
a drop of soap solution.

• Cut out 50 plates of leaves with the hole punch and carefully placed them on paper napkin after

you are complete.

• (Removing the gases out of the spongy mesophyll tissue)

• Remove the piston/ plunger from both syringes. Place the 10 leaf disks into each strings


• Replace the plunger, but be careful not to crush the leaf disks. Push in the plunger until only a

small volume of air and leaf disk remain in the barrel.

• Pull a small volume of water from the prepared cup into the syringe . Tap the syringe to

suspend the leaf disks in the solution. Make sure that, with the plunger inverted, the disks are

suspended in the solution. Make sure no air remains. Move the plunger to get rid of air from the

plunger before you move on.

• Now create a vacuum in the plunger to draw the air out of the leaf tissue. Create the vacuum

by holding a finger over the narrow syringe opening while drawing back the plunger. Hold this

vacuum for about 10 seconds. While holding the vacuum, swirl the left disk, causing the leaf to

sink in the syringe. If the plunger does not spring. you did not have a good vacuum, and you

may need a new syringe.
In this lab the group placed leaf disks into different cups of water based solution and used different amounts of light to test the rate of photosynthesis. The group knows that if the solution has bicarbonate ions and enough light, the leaf disks will produce sugars and oxygen through the process of photosynthesis, allowing the leaf disks to rise. The group wants to find out if different light amount can affect the rate the disks rises.
Primary Question: Does different light amount affect the rate of photosynthesis?
Background Context: Photosynthesis is crucial for the ecosystem and replenishes the Earth's atmosphere with oxygen. The general equation for photosynthesis is 2H2O + CO2+light energy --> CH2O+O2+H2O.
Leaves usually float in water due to the spongy mesophyll layer of leaves which is usually infused with gases (O2 and CO2). Therefore in order to sink the leaf disks in water the group had to vacuum the gasses inside the leaves and replace it with water. In order to test the rate of photosynthesis the group placed the leaf disks in an alternate source of carbon dioxide in the form of bicarbonate ions. When photosynthesis occur the oxygen will slowly accumulate in the spongy mesophyll layer over time allowing the leaf disks to become buoyant and rise in the water. Thus the rate of photosynthesis can be indirectly measured by the rate of the leaf disks rising.
0 0 0 0 0
0 0 0 0 0
0 0 0 0 4
0 0 0 0 5
0 0 0 0 6
0 0 1 0 7
0 0 2 0 8
0 0 4 2 8
0 0 7 5 10
0 0 7 8
0 0 7 10
0 1 9
0 1 10
0 2
0 3
0 3
0 5
0 6
0 8
0 9
0 10
Completely Dark
Room Light
One Lamp (Control)
Two Lamp
Two Lamp + Foil Box
Little Light (Room Light)
No Lights
One Lamp (Control)
Two Lamps
Two Lamps + Tin Foil
The group believes that when the amount of light a leaf disk receives increases than the rate of photosynthesis would also increase. The group knows the chemical process of photosynthesis requires light energy to generate sugar and oxygen(2H2O + CO2+light energy = CH2O+O2), if the amount of light shined upon the leaf disks increases then more oxygen would be produced thus allowing the disks to rise at a faster rate (faster photosynthesis rate).
Our test yielded incredible results. Through our collected data and observations, the team was able to support our hypothesis that the more light we added, the faster oxygen would be created through photosynthesis. Through our results it can be observed that the leaf disks that were exposed to no light were not able to properly conduct photosynthesis, and therefore could not create enough oxygen in the leaf disks for the disks to rise. However, as more and more light energy was added to every other experiment, the time it took for the leaf disks to rise steadily got shorter and shorter. These results compliment our hypothesis by showing that the rate of photosynthesis does increase with the addition of light energy, since in our experiment the more light energy that was added to the disks, the faster it took all the disks to rise. However, One thing that the team was not expecting was the length of time it took the leaf disks to rise, even when under harsh light.
• Repeat the steps above 5 times with the other 50 leaf disks under different light intensities

(see below)

1. In a completely dark environment

2. Room light

3. Using one lamp

4. Using two lamps

5. Using 2 lamps with tin foil surrounding it

Dependent Variable:
Amount of oxygen generated
Independent Variable:
Amount of light
Confounding Variable:
Number of leaves, volume of solution, concentration of solution, temperature
Control Group:
One Lamp
Ten Leaf disks each
Sources of Error
There were two potential sources of error in this lab that the team conducted. The first source of error was that the team might not have extracted all the oxygen from the leaf disks, or could have potentially had more oxygen left in one disk as compared to another disk after extracting the oxygen. This means that the amount of oxygen that each disk had within them when the test first started could have varied, which could have resulted in some rising faster than others (but not because they had a faster photosynthesis rate). A second Source of error was that we got our leaf disks from separate leaves. Even though the leaves we used were from the same plant, the maturity of each leaf could play a key role in our experiment of photosynthetic rate, since more mature leaves could have a higher photosynthetic rate.
Interpretation of results and How the teams Hypothesis was supported:
The team observed the photosynthetic rate in leaf disks in five different trails, over a time span of 30 minutes for each trail. In each of the trails ten leaf disks were exposed to a certain amount of light, which was the variable we changed in the experiment. In the first trail where the leaf disks were exposed to no light none of the leaf disks floated to the surface. In the second trail, where we used only light that was present in the room, the first leaf disk floated to the surface at the 21 minute mark, and at 30 minutes all ten had floated. Our control group was the trail in which we used one lamp to provide light energy for the leaf disks. In this trail the first leaf disk floated at the 15 minute mark, and all floated at the 22 minute mark. Our next trail we used two lamps. The first two disks floated at the 17 minute mark and all of them rose at the 20 minute mark. For our last trail we not only used two lamps, but also encased the leaf disks in a box of reflective material. In this experiment the first four disks rose at the 12 minute mark and all ten rose at the 18 minute mark. From our results one can observe that the leaf disks that were given the most light energy were able to rise at the fastest rate, due to the fact that their photosynthetic rate was expedited by the extra light energy.
ET 50
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