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Running Head: THE EFFECTS OF FRUCTOSE AND SALT WATER ON THE RATE OF
PHOTOSYNTHESIS
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The Effects of Fructose and Salt Water on the Rate of Photosynthesis
Photosynthesis Experiment
Rebecca Morra
Longwood University
THE EFFECTS OF FRUCTOSE AND SALT WATER ON THE RATE OF
PHOTOSYNTHESIS
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The Effects of Fructose and Salt Water on the Rate of Photosynthesis: Photosynthesis
Experiment
Introduction
Photosynthesis is the process by which solar energy is converted into chemical energy
that is necessary to sustain plant life (“BioCoach”). The chemical reactions of photosynthesis are
summarized in the following equation (“BioCoach”).
6CO2 + 12H2O → C6H12O6 + 6H2O + 6O2
Photosynthesis occurs in the middle tissue of leaves, specifically in the chloroplasts of
mesophyll cells (Raven). The chloroplast contains the thylakoid membrane, which is the internal
membrane (Raven). This membrane is organized in stacks called grana (Raven). Light reactions
occur in this thylakoid membrane (“Fast”). As the membrane absorbs the light from the sun, the
water in the cell is separated into individual hydrogen and oxygen atoms (“Fast”). The light
reactions create NADPH, ATP, and oxygen (which is released back into the atmosphere)
(“Fast”). The Calvin Cycle also occurs in the chloroplast, but it occurs outside of the thylakoid
membranes (“Fast”). The carbon dioxide that the plant absorbs from the atmosphere bonds with
the hydrogen atoms that were from the splitting of water (“Fast”). The ATP is converted to ADP
and the NADPH is reduced to NAD (“Fast”). The final product is glucose (“Fast”).
Photosynthesis can be affected by many factors, including light intensity, carbon dioxide
concentration, and temperature (“Photosynthesis”). Another factor that affects the rate of
photosynthesis is the salinity of the water used to hydrate the plant (Murad). Because of these
factors, this lab was conducted to test whether or not the addition of salt and fructose would
THE EFFECTS OF FRUCTOSE AND SALT WATER ON THE RATE OF
PHOTOSYNTHESIS
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affect photosynthetic rate. It was hypothesized that the addition of fructose to the water used to
hydrate the plant would increase the rate of photosynthesis, and the addition of salt to the water
would decrease the rate of photosynthesis.
Methods
An experiment was conducted to test whether or not the rate of photosynthesis would be
affected by the addition of fructose or salt to the water used to hydrate the plant. Three test tubes
were cleaned and labeled according to the type of water that would be put into them. Plain tap
water was poured into one test tube to serve as the control. This was used to measure what the
regular rate of photosynthesis would be without the addition of compounds into the water. Plain
tap water was poured into the second test tube, this time with the addition of 2g of fructose. The
test tube was then shaken until the fructose was completely dissolved into the water. Plain tap
water was also poured into the third test tube, but with the addition of 2g of salt. The test tube
was also shaken until the salt was completely dissolved into the water. Three branches of an
Elodea plant were cut into 14.5 cm pieces. A branch was then placed into each test tube, cut side
up (see Figure 1). Additional water was added to each test tube to top it off. A stopper was then
fitted into each test tube and the solution filled the tube to about ¼ of the length of the horizontal
portion. The meniscus was marked on each tube to note the starting point of photosynthesis. The
test tubes were then placed into a rack under a 60-watt lamp. Each test tube received the same
amount and type of light, environment, and temperature. The Elodea branches were left under
the light for 20 minutes to photosynthesize (see Figure 2). After 20 minutes, the level that the
meniscus had risen to was recorded. A ruler was then used to measure the distance between the
initial meniscus mark and the final meniscus mark using millimeters. The net photosynthesis was
THE EFFECTS OF FRUCTOSE AND SALT WATER ON THE RATE OF
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calculated by dividing the millimeters of movement by twenty minutes. The net photosynthesis
of the salt and sugar water was then compared to the net photosynthesis of the tap water.
Figure 1
Figure 2
Results
Tube #1: Tube #1 was filled with plain tap water. The meniscus rose 12 millimeters (see Figure
3).
To calculate the net photosynthesis in mm/min:
12 millimeters / 20 minutes = .6 millimeters/minute
Tube #2: Tube #2 was filled with tap water mixed with 2g of fructose. The meniscus rose 6
millimeters (see Figure 3). To calculate the net photosynthesis in mm/min:
6 millimeters/ 20 minutes = .3 millimeters/minute
THE EFFECTS OF FRUCTOSE AND SALT WATER ON THE RATE OF
PHOTOSYNTHESIS
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Tube #3: Tube #3 was filled with tap water mixed with 2g of salt. The meniscus remained at the
initial marking (see Figure 3). To calculate the net photosynthesis in mm/min:
0 millimeters/ 20 minutes = 0 millimeters/minute
The Elodea plant that was put into tap water had a net photosynthesis double of what the
net photosynthesis of sugar water was. The Elodea plant had the best photosynthesis rate in the
regular tap water. The addition of salt to the water appeared to have no benefit, and actually
inhibited the rate of photosynthesis.
Figure 3
THE EFFECTS OF FRUCTOSE AND SALT WATER ON THE RATE OF
PHOTOSYNTHESIS
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Movement of Meniscus
Movement of Meniscus (Millimeters)
14
12
10
8
6
Movement of Meniscus
4
2
0
Tap Water
Fructose Water
Salt Water
Soultions
Figure 4
Net Photosynthesis (Millimeters per Minute)
Net Photosynthesis
0.7
0.6
0.5
0.4
0.3
Net Photosynthesis
0.2
0.1
0
Tap Water
Frustose Water
Soultions
Figure 5
Salt Water
THE EFFECTS OF FRUCTOSE AND SALT WATER ON THE RATE OF
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Discussion
The results of the experiment both supported and contradicted the hypothesis. The rate of
photosynthesis was inhibited by the addition of salt to the water, but the rate was not increased
due to the addition of fructose. In fact, the fructose also inhibited the rate of photosynthesis.
Perhaps this is due to osmosis.
Osmosis is the process of water moving across a membrane toward a higher solute
concentration (Raven). Osmotic concentration is the concentration of all solutes in a solution
(Raven). If there are unequal osmotic concentrations between two different solutions, the
solution with the higher concentration is considered hypertonic (hyperosmotic), and the solution
with the lower concentration is hypotonic (hypoosmotic) (Raven). Solutions are isotonic
(isosmotic) when they have equal osmotic concentrations (Raven). When a cell is in a hypotonic
solution, the cell swells because the solution diffuses through the cell wall and enlarges the body
of the cell (Raven). The pressure from inside the cell causes the entire cell to bulge (Raven).
When a cell is in a hypertonic solution, however, water diffuses out of the cell into the
surrounding solutions, causing the cell to or shrink (Raven). The control in this experiment (the
tap water) was isotonic because the rate of photosynthesis was not inhibited or increased, and the
cells therefore remained the same size. Perhaps the salt water in this experiment inhibited the
photosynthetic rate because it was a hypertonic solution, causing the plant cell to shrink from the
cell wall and therefore decrease the meniscus’s movement (the rate of photosynthesis) (Raven).
Perhaps the fructose water also inhibited the photosynthetic rate because it was a hypertonic
solution as well, but not as hypertonic as the salt solution (since the movement of the meniscus
was inhibited, but not as much as the salt solution). Though the hypothesis of this experiment
THE EFFECTS OF FRUCTOSE AND SALT WATER ON THE RATE OF
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was not proven completely correct, this experiment did lead to some interesting findings. It
would be intriguing to apply these discoveries to the outside world and determine how
environmental factors such as drought would affect photosynthetic rate. It would also be
interesting to discover how increasing the salinity in water could affect not only the plants
themselves, but also the surrounding environment.
THE EFFECTS OF FRUCTOSE AND SALT WATER ON THE RATE OF
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Works Cited
"BioCoach Activity." Pearson. N.p., n.d. Web. 07 Oct. 2015.
Murad, A. M., Molinari, H. C., Magalhães, B. S., Franco, A. C., Takahashi, F. C., de Oliveira-, N. G.,
& ... Quirino, B. F. (2014). Physiological and Proteomic Analyses of Saccharum spp. Grown
under Salt Stress. Plos ONE, 9(6), 1. doi:10.1371/journal.pone.0098463
"Photosynthesis and Limiting Factors." Structure and Functioning of Seminatural Meadows
Developments in Agricultural and Managed Forest Ecology (1993): 193-210. Web. 7 Oct. 2015.
"Photosynthesis Fast and Simple." YouTube. YouTube, n.d. Web. 07 Oct. 2015.
Raven, Peter H., and George B. Johnson. Biology. Boston: McGraw-Hill, 2002. Print.