Download The Effect of Light Proximity On the Rate of Photosynthesis

INVESTIGATION 5: PHOTOSYNTHESIS
The Effect of Light
Proximity On the Rate of
Photosynthesis
by Hadeel Haidar
AP Biology, Mr. Harrison
January, 2014
Lab Partners:
Jordan Works
Fatima Albrehi
Sarah Anderson
ABSTRACT
Many factors affect the rate of photosynthesis in living leaves. In this lab, the distance between
the plant and its light energy source was being controlled by the experimenters. To do so, living spinach
leaf disks were placed into cups filled with a sodium bicarbonate mixture. Three of these cups were
placed at different distances from a clamp light containing a 42Watt fluorescent light bulb. It was found
that the disks in the cup closest to the light seemed to have risen the fastest, while the cup furthest away
from the light took triple the amount of time. It can be concluded through this experiment that the
hypothesis tested was in fact true. The rate of photosynthesis was increased as the plant’s proximity to
the light source increased.
INTRODUCTION
Autotrophs sustain themselves through a process called photosynthesis. This is a process by
which plants and other specific organisms transform light energy into chemical energy. Although, this
process goes beyond just this. Photosynthesis underlies nearly all life on earth, directly or indirectly, it
nourishes almost the entire living world (Campbell and Reece’s Biology, 7th Edition, 2005). This lab
primarily focuses on the rate of photosynthesis, specifically, different factors that may affect it. A point
that illustrated itself to be a factor when it comes to the rate of photosynthesis is the type and quantity of
chlorophyll. The concentration of chlorophyll directly affects the rate of photosynthesis in that it absorbs
the light energy that sets off the reaction. Special pigments in a plant help it to create energy by
absorbing this light energy. Pigments absorb and reflect certain types of light waves with particular
wavelengths. All green plants have a large amount of chlorophyll to reflect green light, but they also
contain carotene and xanthophylls, but these pigments are overpowered by the strong pigment of
chlorophyll a and chlorophyll b (Molecular Cell Biology, 4th Edition, 2000). A way to analyze and
compare these photosynthetic pigments is through chromatography. This type of chromatographic
experiment was put to action, and the results clearly showed the four pigments. It’s known that plants
with a dark green tint have the fastest rate of photosynthesis because it contains a high abundance of
chlorophyll a.
Another way to determine the rate of photosynthesis is by controlling the amount of light energy
that reaches the plant. Light energy is a key factor in the process of photosynthesis, as shown in the
chemical formula for photosynthesis,
6H2O + 6CO2 + light energy­­­­­­­­­­> C6H12O6+ 6O2 ,so by controlling the distance the plant is from
the light is the way the rate of photosynthesis was measured in this lab. The main objective of this lab
was to test the hypothesis that the closer a plant is to the light source, the faster the rate of
photosynthesis. To test this hypothesis, an experimental lab was conducted with a very specific
procedure. The purpose of this lab was to find a strong factor that plays a key role in the rate of
photosynthesis and manipulate it to create the optimal photosynthesis rate. To test this hypothesis, the
experiment involved the preparation of leaf disks derived from living spinach leaves. These spinach disks
were placed in three cups filled with a mixture of a sodium bicarbonate solution and dish soap. The dish
soap served as a water­repellent barrier on the leaf surface so sodium bicarbonate can get inside, and
the sodium bicarbonate served as a source of carbon dioxide when dissolved in the solution. These
three cups were then placed at different distances from the light source. The light source used was a 42
Watt fluorescent light bulb placed in a clamp light. The results of this procedure helped come to a
conclusion that supported the hypothesis that the closer a plant is to the light source, the more the rate of
photosynthesis increased.
METHODS
Procedure: Floating Leaf Disks
Materials:
Baking Soda (HCO3)
350 mL Beaker
Hole Punch
Liquid Soap (Approximately 5 Plastic syringe without needle Glass Stirring Rod
mL of dishwashing soap in 250 (10 mL)
mL of water)
Three Plastic Cups
(30mL/30cc)
Living Spinach Leaves
Timer
Light Source (42Watt)
Clamp Lamp
Electronic Balance
Pipette
(This photo derived from lab)
Prior to beginning the lab, safety precautions were taken into account to avoid the risk of
harmful injury. Precautionary measures such as wearing goggles throughout the duration of the lab were
put to action, for the most part. Working in close proximity to exposed light bulbs can be a safety
hazard. These light bulbs can easily be shattered, so extra stress on light bulb treatment was put into
account. With the supervision of a licensed teacher, the lab was put into action.
To begin, a homogenous mixture of bicarbonate and water was prepared. A 350 mL beaker
was obtained and filled with 300 mL of water straight from the tap. Using an electronic balance, 1.5g of
sodium bicarbonate was measured out. The baking soda was then poured into the 350 mL beaker filled
with the 300 mL of water. Using a glass stirring rod, the two compounds were mixed together evenly,
creating a bicarbonate solution
Three plastic 30 mL cups were filled with this solution prepared previously. To distinguish
between the cups, the cups were labeled using masking tape. The cups were labeled, “Cup 1,” Cup 2,”
and “Cup 3.”
With the help of lab partners, the next preparations were completed simultaneously for the three
cups.
Using a pipette, one drop of a diluted liquid soap solution was added to each cup. To avoid the
formation of suds, the soap was not mixed into the solutions. These cups were then put aside to prepare
the living leaves.
To prepare the spinach leaf disks, living spinach leaves were provided by the teacher. Using a
hole punch, and avoiding major veins, 10 circular disks were punched out of the spinach leaves. This
was done thrice totalling to 30 spinach disks.
(This photo derived from lab)
The pistons on each of the three 10mL syringes were then removed and put aside. 10 leaf disks
were then placed into each of the syringes. To get the disks to the bottom of the syringe without getting
crushed, air was blown in from the top opening. To target any specifically that didn’t follow suit, a thin
glass mixing rod was used to detach the disk away from the inner wall of the syringe and into the
bottom.
The pistons were then replaced back into the syringes and pushed in until only a small volume of
air and leaf disks remained in the barrels. Pulling back on the plungers, 5mL of the sodium bicarbonate
solution was pulled into each syringe from its coordinating cup (each syringe to a cup). The syringes
were then inverted and tapped a few times to suspend the disks in the solution.The plungers were then
adjusted in which there was no air remaining.
Next, vacuums were created in the plungers by holding a finger over the narrow syringe
openings whilst drawing back the plunger. These vacuums were held for 10 seconds while shaking the
syringes vigorously until the plungers sprung back and the leaf disks sunk to the bottom of the solutions
with the syringes inverted.
The disks and solutions were then poured into their appropriate clear plastic 30mL cups. To do
this, the solutions were first pushed out from the spouts of the syringes. The pistons were then removed
and the leaf disks were poured out. Air was blown in from the nozzle for the troublesome disks to help
them get into the cup.
At this point, the light was to be set up. A clamp lamp with a 42W fluorescent light bulb was set
28cm from the top surface of the lab table. To set the three cups different distances from the same light
bulb, a staircase like set was created using numerous text books. In doing this, the 1st cup was set
11.75cm away from the lamp on the top book, the 2nd cup was set 17cm away from the lamp, and the
3rd cup was set 28 cm away, at the base of the “staircase.”
As soon as the cups were positioned so that they all received their designated amount of light,
the timer began. The timer used for in this lab came from an app called Lab Timer; an app suggested by
the teacher. At the end of each minute, the number of leaf disks that floated to the top of the plastic cups
were recorded. This data was collected until all of the disks from all three of the cups floated.
In completing this past step, all materials used were put away responsibly. Suggested caution is
to be taken particularly when disassembling the light bulb from the clam light. This cautionary step goes
out to putting away the rest of the materials in their designated spot.
RESULTS
Procedure 1: Floating Leaf Disks
The data from this procedure demonstrates the rate of photosynthesis by measuring the rate in
which spinach leaf discs floated to the top of a Sodium Bicarbonate solution at different distances from
the light source.
Figure 1.1 shows the rate of leaf disks that floated per minute, while also keeping track of the
total number of disks. Container 1 was placed 11.75cm away from the clamp light, the closest of the
three cups. No visible change occurred within the first minute of being exposed to the light energy
source. Within two and three minutes a pattern arose of 1 per minute. Unfortunately, no disks arose
within the fourth minute. A boost of three disks floated within five minutes, and another three within 6
minutes. The last two disks floated at seven minutes. The entire process for the first container took 7
minutes and 2 seconds.
Figure 1.1
Figure 1.2 shows the rate of spinach leaf disks that floated during the procedure in cup 2. This
cup was distanced 17 cm away from the clamp lamp light source. The disks began to rise slowly, not
rising until the 3rd minute. The three that floated within 4 minutes made up for lost time, and then the rate
slowed down again going into the 5th minute. One rose at the 5 minute mark, but none going into the 6th
minute. Another disk rose at 7 minutes, but again, nothing at 8 minutes. When it came to the 9th minute,
two more disks popped up. One more rose at the 10 minute mark, and the final disk rose within 11
minutes. The total time for all 10 disks to rise was 11 minutes and 2 seconds.
Figure 1.2
Figure 1.3 shows the rate of rising leaf disks in the third cup. This last container was placed
28cm away from the clamp light, the furthest of the three cups. No visual change occurred to the third
cup until the 4th minute that two leaf disks rose to the top. The next disk that floated to the top was at
the 6th minute. For the next two minutes, no change occurred until 3 disks quickly rose. One disk arose
at at 10 minutes, and two more came up at 11 minutes. One more disk remained, and it took 14
minutes for it to finally come up. It wasn’t until 25 minutes that all 10 disks were risen.
Figure 1.3
Figure 1.4 shows how many disks floated within a time frame of 7 minutes. This is the time it
took for all 10 of the disks in cup 1 to float to the top. Just over half of the disks in cup 2 floated to the
top within this time. Only two of the 10 disks in cup 3 floated up in 7 minutes.
Figure 1.4
Figure 1.5 compares the time it took for 50% of the disks to rise between the three cups. This
graph shows that it took 5 minutes for both container one and container two to reach their ET50. Unlike
the first two cups, cup three did not follow through with this trend. It took nine minutes for cup three to
reach its ET50 of 5 leaf disks.
Figure 1.5
DISCUSSION
The hypothesis stating that the rate of photosynthesis was increased as the plant’s proximity to
the light source increased was supported by the results of this lab experiment. As shown in figure 1.4,
cup one took the least amount of time to fully photosynthesize. Cup one was the closest to the light
source; it was 11.75 cm away from the lamp. Comparing this to container three, it can be seen in figure
1.5 that this container took the longest amount of time to reach its ET50 of 5 disks. Container three
took 9 minutes, as opposed to the first and second container that only took 5 minutes to reach their
ET50. Container three was the furthest away from the lamp light with a distance of 28 cm. Figures 1.1,
1.2, and 1.3 show the individual cup results. These graphs show the rate of photosynthesis per minute.
It measured the number of spinach leaf disks risen per minute.
The amount of light that reaches a plant while undergoing photosynthesis is a factor that can limit
it. If the plant is brought closer to the light source, the plant is exposed to more light, while increases the
light intensity the plant is absorbing. The reason that more light allows for an increase in the rate of
photosynthesis is that light excites chlorophyll molecules, which in turn provides the energy for
production of carbohydrates (glucose). As light is added to a plant, more and more energy is used to
stack H+ ions across the membrane from water around the cell to create a concentration gradient. As
these H+ protons begin to float back to the outside of the cell, they go through ATP synthase, thus
creating ATP energy. So as the distance between the plant and the light source is increased, more ATP
is created.
The experiment described in this report was designed to answer the question of, “What factors
affect the rate of photosynthesis in living leaves?” As proven in this lab, the proximity of a plant to its
light source is an important factor in the way that it affects the rate of photosynthesis in living leaves.
Through the procedure created, it was shown that the cup of HCO3 mixture and living spinach leaves
closest to the light source, 42 Watt fluorescent light, had the quickest rate of photosynthesis. When
considering distance as an important factor, it should be considered that there is also a point to where
too much light can in turn harm the plant and decrease the rate of photosynthesis. Photosynthesis has an
optimal temperature of approximately 30 degrees Celsius. If this lab were to be redone, the temperature
would have been taken to add to distance having an affect on the plant.
CONCLUSION
This lab was a great way to learn about the depths of photosynthesis. It seems that these factors
that affect the rate of photosynthesis can be supremely underated, when in fact they have a huge impact
on the way plants develop. Using and studying these types of factors can lead scientist to large
breakouts in science. Studies revolved around the rate of photosynthesis can be used to create seeds to
plants that can grow fully within weeks. These plants can then be tested on, manipulated, all to a
scientists’ liking.
Being put in a position where the opportunity to chose a factor to focus on was a great way to
pick up on the lab and create an almost personal relationship with the procedure created; especially the
little spinach leaf disks. A particularly interesting aspect of this lab was learning to create a vacuum with
a syringe. This was a skill that the experimenters can hold for future lab experiments.
QUESTIONS
What causes the disks to rise?
If an opposing factor acted against one that was proven to increase the rate of photosynthesis, which
would ultimately have a great impact?
Does the concentration of CO2 effect the experiment?
If a light bulb with a stronger wattage was used, would this change the response to the hypothesis?
RESOURCES
Campbell and Reece’s Biology, 7th Edition, 2005
http://www.ncsec.org/cadre2/team24_2/Plantpigments.htm
http://www.courseworkbank.info/courseworkbank.info.php?f=R0NTRS9CaW9sb2d5L0ludmVzdGln
YXRpbmcgRmFjdG9ycyBBZmZlY3RpbmcgdGhlIFJhdGUgb2YgUGhvdG9zeW50aGVzaXMucGRm
http://www.ncsu.edu/labwrite/Experimental%20Design/explabs_intro1­2.htm
http://answers.yahoo.com/question/index?qid=20091025162503AAPNklS
http://www.ncsu.edu/labwrite/res/labreport/res­sample­labrep1.html
http://wiki.answers.com/Q/How_does_the_distance_from_the_light_affect_photosynthesis?#slide=2\
http://www.ncbi.nlm.nih.gov/books/NBK21598/