What Factors Affect the Rate of Photosynthesis in Living Leaves?

Abstract:
In this lab, four different types of leaves were tested to see the rate at which each leaf photosynthesized. This lab demonstrates how plants store light, capture light, and use light as energy for reproduction and growth, by photosynthesis. The control in this experiment was spinach, which was tested before any of the other plants were. The other plants that were tested were English Ivy, C4 Plant, and a multicolored plant. Each type of leaf was tested in a sodium bicarbonate solution and a solution of distilled water. It will be shown in the discussion whether the hypothesis made was correct or incorrect. It will be shown in the discussion what could have occurred during the experiment that could have affected the results. Introduction:

Photosynthesis can be defined as the process by which green plants, and other organisms make carbohydrates from carbon dioxide and water in the presence of chlorophyll, using energy captured from sunlight by chlorophyll, and releasing excess oxygen. Like all enzyme-driven reactions, the rate at which photosynthesis occurs can be measured by the disappearance of a certain substrate, or the accumulation of product. Photosynthesis consists of light reactions and dark reactions. This process can be simplified by the equation: 6CO2 + 6H2O + Energy –> C6H12O6 + 6O2

Shown in this equation 6 molecules of carbon dioxide (6CO2) and 12 molecules of water (12H2O) being consumed in the process, and glucose (C6H12O6), six molecules of oxygen (6O2), and six molecules of water (6H2O) being produced. The energy source is photons (light) from the sun. The rate of photosynthesis could be measured by the amount of moles of O2 produced for one mole of sugar. The rate of photosynthesis could also be measured by the amount of moles of CO2 that are consumed for every mole of sugar that is synthesized. Leaf disks float in water, most of the time. If air spaces are infused with CO2, however, the density of the disks will increase. When sodium bicarbonate is added to water, the bicarbonate will cause the disks to sink. As photosynthesis continues, oxygen is released into the leaf disks, changing the ability of the leaf disks to float in water, and causing them to rise.

Since cellular respiration is taking place at the same time inside of the leaf disks, the oxygen generated by photosynthesis will be consumed. As a result, the rate at which the disks will rise is proportional to the net rate of photosynthesis. In this experiment, the rates of photosynthesis of various plant leaves were tested. The plant used as the control in this experiment was spinach. The spinach leaf was put under the influence of an intense light source and tested in distilled water, as well as sodium bicarbonate. The other leaves that were tested were: C4 plant, English Ivy, and a Multicolored Leaf. All three of these diverse plants were tested under the same conditions as the spinach leaf. The hypothesis given for this lab is that the leaf disk will all float to the top of both solutions within 15 minutes. *Hypothesis* the leaf disks will all have risen to the top of the solution within 10-15 minutes, except the disks in pure water.

Materials:
* Timer
* 60 watt light bulb
* Hole puncher
* Baking soda (sodium bicarbonate)
* Liquid soap (approximately 5 mL of dishwashing soap in 250 mL of water) * 2 plastic syringes without needle (10 mL or larger)
* Plant leaves (spinach, ivy, C4 plant, and multicolored plant.) * 2 clear plastic cup

Procedure:
1. Prepare 300 mL of 0.2% bicarbonate solution for each experiment. (The bicarbonate will serve as a source of carbon dioxide for the leaf disks while they are in the solution.) 2. Label the first cup “CO2”

3. Pour the bicarbonate solution into a clear plastic cup to a depth of about 3 cm 4. Label the second cup “No CO2”
5. Fill a second cup with only water, this is to be used as the control group for this experiment 6. Prepare the materials for both cups simultaneously so that the results are not skewed 7. Add one drop of a dilute liquid soap solution to each cup using a pipette. If there are bubbles present, make sure to get rid of them before continuing the experiment. The soap in this case is used to wet the hydrophobic surface of the leaf, allowing the solution to be drawn into the leaf and enabling the leaf disks to sink in to the fluid. 8. Use a hold puncher to cut 10 leaf disks for each cup. Avoid hold punching around the ribs of the leaf. 9. Draw the gases out of the spongy mesophyll tissue and infiltrate the leaves with the sodium bicarbonate solution. This should be done as follows: 10. Place 5 of the leaf disks into each syringe

11. Place the plunger back in to the syringe, without crushing the disks. Push in the plunger until only a small volume of air along with the leaf disks remain in the syringe 12. Put a small volume (around 5 cc) of sodium bicarbonate with the soap solution from the prepared cup into one syringe and a small volume of water with soap into the other syringe. 13. Tap each syringe. Assure that the disks are in the solution, after the plunger is inverted. Also, assure that there is no air remaining.

Make sure no air remains. 14. At this point, a vacuum is to be created within the syringe to draw the air out of the tissue of the leaf disks. After this step, the experiment is really quite simple. 15. To create the vacuum, hold one finger over the narrow part of the syringe while drawing back the plunger. 16. While holding the vacuum, swirl the leaf disks to suspend them in the solution. 17. Release the vacuum. The solution will infiltrate the air spaces in the leaf disks, which will cause them to sink. This procedure may have to be repeated a couple of times if it does not work the first time. 18. Pour the solution, along with the disks, from the syringe into the appropriate clear plastic cup. 19. Place both cups under the light source and start the timer. At the end of each minute, record the number of disks that have risen, if any. Assure that no disks are stuck to the side of the syringe. 20. Report observations, and repeat process until all of the types of leaves have been tested.

Results
Shown in the following charts is the number of disks floating in each solution along with the time that it took for each disk to rise. The light sours used was placed 29.5 cm away from the cups in which the disks were placed in. Spinach leaf disks in Sodium Bicarbonate

Number of disks floating| 1| 2| 3| 4| 5|
Minutes| 1:57| 5:58| 6:14| 10:02| 18:33|
The spinach leaf in this experiment was used as the control. All other data was compared to that of the spinach leaf disks.

Spinach leaf disks in distilled water
Number of disks floating| 1| 2| 3| 4| 5|
Minutes| 0:00| 0:00| 0:00| 0:00| 0:00|
When the spinach leaf disks were dislodged in to the distilled water, none of them rose at any given time. For this reason, “0:00” was put in to the time row.

English Ivy in Sodium Bicarbonate
Number of disks floating| 1| 2| 3| 4| 5|
Minutes| 1:13| 5:07| 12:09| 15:13| 21:07|
All 10 disks had floated by 21 minutes and 7 seconds.

English Ivy in distilled water
Number of disks floating| 1| 2| 3| 4| 5|
Minutes| 17:09| 18:31| 19:16| 21:48| 28:14|
The English Ivy leaf disks took a longer time to rise, however they did end up rising towards the end of their timing.

Multicolor Plant in Sodium Bicarbonate
Number of disks floating| 1| 2| 3| 4| 5|
Minutes| 1:04| 11:43| 19:12| 26:05| 32:11|

Multicolor Plant in distilled water
Number of disks floating| 1| 2| 3| 4| 5|
Minutes| 1:08| 22:16| 23:52| 27:37| 33:02|

C4 plant in Sodium Bicarbonate
Number of disks floating| 1| 2| 3| 4| 5|
Minutes| 1:12| 1:26| 1:28| 7:09| 14:11|
The disks of the C4 plant rose rather quickly, much faster than the other plants did in the bicarbonate.

C4 Plant in distilled water
Number of disks floating| 1| 2| 3| 4| 5|
Minutes| 14:38| 23:04| 26:48| 30:52| 34:45|

Discussion

The hypothesis made at the beginning of the experiment proved to be wrong. It was hypothesized that all of the disks would have risen by 10-15 minutes, which was not the case. Also, it was predicted that the plants submerged in to the distilled water would have no results, which was also proven wrong. All but one of the plants that were put in to water had shown results. Likewise, all but the C4 plant in Sodium Bicarbonate solution had taken over 15 minutes to have all of the leaves float to the top of their solution. It was proven in this experiment that the rate of photosynthesis can be affected by the type of plant that is being tested on. For example, the Ivy plant in water and the multicolored plant in water had completely different results. It took a little over 1 minute for a disk to rise in the multicolored plant, while it took around 17 minutes for a single disk to rise in the Ivy plant. Many errors could have occurred in this experiment. Precise timing was crucial, and if the disks were not submerged in to their solution simultaneously, the results could have come out inaccurate. There were issues regarding the spinach leaf disks, which could have been the reason why the ones that were put in to water showed no results.

Conclusion
Photosynthesis and the rate at which it occurs was shown in this experiment. The different results from each type of leaf in the Bicarbonate solution and water shows how photosynthesis can be affected by different types of plants and the substance they are soaked in. The hypothesis posed before the experiment had taken place was proven wrong.

References

Cellular Processes: Energy and Communication lab packet.
http://www.ncsu.edu/labwrite/Experimental%20Design/explabs_checklist.htm http://www.mathsisfun.com/data/standard-deviation.html