The temperature of the water stayed a constant at about 29.5O C throughout the experiment.
Conclusion:
From the results that I have gathered I can state that an increase in light intensity certainly does increase the rate of photosynthesis. As was also expected in my prediction, the relationship between light intensity and the rate of photosynthesis was non-linear. From both graphs there is a best-fit curved line. This means that the rate of photosynthesis increases at an exponential rate.
However, my prediction that light intensity is inversely proportional to the distance squared did not fit into my results perfectly. The rule existed but there was often quite a large margin of error.
When measuring light intensity in terms of distance, the greater the distance, the slower the rate of photosynthesis. While the rate of photosynthesis was decreasing, the rate at which it was decreasing at was also decelerating. This is where the line in graph 1 shallowed.
When measuring the light intensity in terms of LUC, the greater the distance, the slower the greater the rate of photosynthesis. While the photosynthetic rate increased, the rate at which it increased was decreasing. This is where the line in graph 2 shallows.
The shallowing of the line in graph 1 can be explained by the fact that light intensity is inversely proportional to the distance squared. This means that as distance increases the light intensity decreases at an exponential rate. If light intensity decreases exponentially, photosynthetic rates that depend on light intensity also decreases exponentially. The line in graph 1 would eventually reach "0" where photosynthesis stops as light intensity limits this rate.
The shallowing of the line in graph 2 is due to other factors limiting the rate of photosynthesis. These other factors do not immediately limit the rate of photosynthesis but rather gradually. As light intensity increases the photosynthetic rate is being limited by certain factors such as carbon dioxide and temperature. As light intensity increases further, these factors limit the rate of photosynthesis even more until photosynthesis is completely limited and the graphed line become horizontal. This is when photosynthesis is being carried out at a constant rate.
The reason that a "f 1/b2 did not apply was due to the apparatus used. The lamp that I used had a cover that directed the light energy somewhat. The light energy did not spread out as much as a plain light bulb with no cover. The distribution of the light energy was more concentrated, changing the gradient of the graph.
Evaluation:
Overall, I would state the experiment as a success since my predictions were supported by my results. This is important in reflecting success only if my prediction was sensible and logical. Just as important is where the experiment was not a success and why. This photosynthesis investigation was probably not performed as accurately as it could have been due to some controllable and uncontrollable conditions. Some mistakes can be corrected.
While performing the experiment, the piece of pond weed did not photosynthesize at a steady rate, even when the distance from the plant to the light source was kept a constant. The second reading at 0 cm was far greater than the first reading at 0 cm. While the number of oxygen bubbles was being recorded, the rate at which the plant was photosynthesizing had increased several times. This may be due to the poor circulation of sodium hydrogen carbonate at the beginning of the experiment. Carbon dioxide may have initially limited the rate of photosynthesis. The readings at 0 cm and 5 cm were repeated many times until the rate of photosynthesis had begun to settle. From then on, there were no more similar problems during the experiment. To make sure that the there
The negative effects from this problem may be inaccurate data for some readings. These would show up on my graph. However, there seemed to be few anomalies than was expected when the experiment was being performed. Almost all readings were in correlation with each other and all of the anomalies were in the high photosynthetic rate end of the results. This was when the distance from plant to light source was 0 cm or only 5 cm.
A large factor in determining data accuracy is the amount of human error during experiments. The rate at which oxygen bubbles were being produced by my plant was so high that I found it difficult to count the amount of bubbles. I estimate a margin of error of at least 3 bubbles for each reading taken. To improve the accuracy of the results, the readings would have to be taken several more times. The entire experiment could have been performed again, and the new results could be combined if the same plant is used. But the photosynthetic rate of the same piece of pond weed would eventually decrease over time anyway. Repetitions would, however, improve the overall reliability of the results.
There are quite a few factors that could affect the results of my experiment. Some of these are variables that were mentioned earlier and could not be controlled, or they were variables that were not initially considered.
While performing the experiment, some of the oxygen produced from photosynthesis may have dissolved into the water. Some oxygen may have even been used by micro-organisms living on the pond weed. The amount of oxygen dissolved or used by microbes is probably insignificant to my results since the degree of accuracy at which I measured was not high enough. Some oxygen is also used during the respiration of the plant. But since only bubbles were counted, the volume of bubbles was not as important. But to volume of oxygen produced is important, since it was volume in terms of bubbles that were measured. As the rate of photosynthesis decreased due to a decrease in light intensity, the size of the bubbles produced also became smaller. This change in bubble size was no accounted for when the results were analyzed. For a more accurate analysis of the collected data, volume should have been measured instead of bubble quantity since the size of bubbles can vary. Using a capillary tube in place of the test tube so that the volume of each bubble could have been measured could have done this.
During the high intensities I had experienced counting difficulties of the bubbles being produced. There are also factors affecting accuracy at low light intensities. With low light intensity, the pond weed receives some light energy from background light such as sunlight seeping through curtains or the light from the lamp of another student's experiment. To eliminate most all background light, the experiment must be performed in a completely dark room. Even then, some of the light from the lamp in my experiment would reflect of the table and reach the plant though this amount of light is probably insignificant in affecting the rate of photosynthesis.
Temperature was also another factor that was controlled by the lamp being used. Even though a glass block was used in front of the lamp to prevent some heat from reaching the plant, not all the heat can be blocked. The extra heat, however, did not affect the temperature of the water, which stayed at between 290 and 300 C.
The method of the experiment could probably also be improved to obtain more reliable results. As already mentioned, the a capillary tube should be used in place of a test tube to accurately measure the volume of the oxygen produced. Due to the high rates of photosynthesis of the pond weed, readings should be taken within shorter time periods. I had originally chosen to count the number of bubbles in one minute but this produced miscounts in the readings. If during a repeated experiment, counting bubbles is still used, there is a smaller chance for human error when counting within a smaller time frame. If the capillary tube option was to be chosen, volume should be measured for a smaller time frame to reduce the overall time to complete the experiment. Also, during high rates of photosynthesis, it would still be difficult and impractical to measure the volume of oxygen produced for a long duration.
Due to the nature and convenience of the experiment, it could be easily modified to investigate another variable of photosynthesis. Since sodium hydrogen carbonate (NaHCO3) is used to provide the pond weed with carbon dioxide. The amount of CO2 could be varied by performing the experiment with different volumes of NaHCO3. The plant would be kept at a constant distance from the lamp and a constant volume of water would be added to the sodium hydrogen carbonate. Another experiment using almost identical apparatus would be to vary the color of the light the plant absorbs. This could be varied by using translucent color filters in front the lamps. Since light wave length has already been identified as a variable of photosynthesis, it would be interesting to actually test it. The only problem of this experiment is that there is no way to define or "measure" the color of light. Wave length would be a solution but this cannot be measured with available equipment. We only have a general idea of how to class colors. Because of this, the colored light experiment should not be taken as seriously as light intensity or carbon dioxide.
photosynthesis
PHOTOSYNTHSIS INFORMATION:
The Nature of Light
Light behaves both as a wave phenomenon and as discrete particles of energy called photons. If we look at light as a wave phenomenon, we can assign it a wavelength (the distance from one peak of the wave to the next) and an amplitude (the distance the wave oscillates from its centerline). Different wavelengths of light have different characteristic energies and properties. Light can also travel at various speeds in different media, producing a frequency at which the wave travels. The energy contained in a wave of light is related to its frequency.
Where E is energy, h is Planck's constant Energy = (6.626196 * 10^-34 Joule-seconds), and c is the speed of light. Short wavelengths have high energies and long wavelengths have lower energies.
Pigments
How is light captured by living things? Molecules, when struck by a wave or photon of light, reflect some of its energy back out, or it can absorb the energy, and thus enter into a higher energy or excited state. Each molecule absorbs or reflects its own characteristic wavelengths of light. Molecules that have evolved to absorb wavelengths in the visible region of the spectrum very well are called pigments.
Absorption and Action Spectra
An absorption spectrum for a particular pigment describes the wavelengths at which it can absorb light and enter into an excited state. The following diagram represents the absorption spectrum of pure chlorophylls in solution:
An action spectrum, on the other hand, describes the efficiency of a particular molecule at acheiving its purpose in absorbing light; this measurement shows what wavelengths of light the molecule can trap to conduct photosynthesis. And action spectrum closely follows an absorption spectrum for a particular pigment because the molecule has to be able to absorb light to enter into its excited state and pass the energy along.
Chlorophylls and the Accessory Pigments
Chlorophyll is a generic name for green pigments in plant cells....a substance that absorbs visible light primarily in the red, violet and blue regions of the light spectrum. There are several kinds of chlorophyll with chlorophyll a being the most important for light dependent reactions in the complex photosynthesis processes. Chlorophyll a and b exist in plastids in cells of higher plants while chlorophyll c,d and e are present only in algae. Photosynthesis is the process of converting light energy into chemical energy which can only be performed by plants. All life on earth depends upon the ability of plants to photosynthesize simple sugars which are the basic source of food from which all other forms of food originate.
A chlorophyll molecule is made up of carbon and nitrogen atoms joined in a complex ring with an atom of magnesium located in the center of the ring. The molecule has a long chain of 20 carbon atoms making up an alcohol "tail" attached to the ring. Each kind of chlorophyll may vary somewhat in its molecular structure giving it slightly different chemical and physical properties.
Chlorophyll appears to have three functions:
It serves as antennae to absorb light energy. In this process it becomes "excited" (it produces electrons that exist beyond their normal "ground" state and are in a "charged"condition, so to speak, ready to move elsewhere as a source of electrical energy.
Chlorophyll transfers H+ electrons by a process known as resonance transfer across thylakoid membranes to P700 and P680 type chlorophyll a molecules.
Chlorophyll, with the aid of enzymes, converts light energy into chemical energy by a complex series of processes of oxidation involving loss of electrons. In these processes carbon dioxide and water are converted to glucose and oxygen.
aim
I aim to investigate the effects of the quantity of light and thus the light intensity on the rate of photosynthesis in Elodea.
background
Photosynthesis is the production of food compounds from carbon dioxide and water by green plants using energy from sunlight, absorbed by chlorophyll ie. photosynthesis is how plants feed.
lightlightlil
6CO2 + 6H2O ◊ C6H12O6 + 6O2
Raw materials Products
ie. Green plants make organic substances from inorganic substances.
In order to keep the equation for photosynthesis simple, glucose is shown as the only food compound produced. However, this does not mean that glucose is not the only food compound produced.
The process of taking in and giving out gases is known as gaseous exchange. When green plants photosynthesise, they take in CO2 and give out O2. This only happens in daylight when light is available as an energy supply. The exchange of gases in green plants in light is the opposite of that of animals; however this does not mean that green plants do not respire. During daylight, plants photosynthesise and respire at the same time, hence all CO2 produced by the plant during respiration is transformed into O2 and food (and thus energy) for the plant. It is only when the rate of photosynthesis is greater than the rate of respiration that CO2 will be taken in and excess O2 given out.
ie. In darkness O2 is taken in and CO2 is given out - there is no p/s; in dim light the rate of respiration and p/s is equal - there is no gaseous exchange with the air; in bright light however p/s is faster than respiration and thus O2 is given out - CO2 is taken in to use for p/s and the CO2 made from the plant's respiration is also used to make O2.
ie. The more light (the higher the light intensity), the greater the rate of p/s - unto the LSP [see below].
If a plant is given plenty of sunlight, carbon dioxide and water, the limit on the rate of p/s is the ability of the plant to absorb these materials and make them react. (eg. total number and capacity of chloroplasts and the physical limitation of carbon dioxide diffusion.) Most of the time plants DO NOT have an unlimited supply and so the rate of p/s is not as high as it might be.
Blackman's Law states that:
"The factor in least supply will be the limiting factor."
As the light intensity (LI) increases, the rate of p/s increases, until the plant is photosynthesising as fast as it can - the LSP - Light Saturation Point. When the LSP is reached, plants cannot photosynthesise any faster, even when the light gets brighter. From this point on, according to Blackman's Law, the factor in least supply will be the limiting factor ie. either CO2, H2O or temperature will be the limiting factor.
As the amount of CO2 available increases, the rate of p/s increases, until the plant is photosynthesising as fast as it can - the CSP - CO2 Saturation Point. If both CO2 and light supply are increased together, the rate of p/s will level out. Henceforth it is limited, according to Blackman's Law, by the factor in least supply, either H2O or temperature. however there is a physical limitation of the carbon dioxide diffusion and the plant's sunlight absorption.
At a lower temperature, the rate of p/s is increasing with increasing LI or CO2 availability, but the LSP or CSP is quickly reached. At a higher temperature, the rate of p/s increased further and reaches the LSP / CSP slower. Thus we can se that temperature affects the rate of p/s - it is higher at higher temperatures.
From this information, one can see that if one wants to investigate solely the effect of the quantity of light on Elodea, one must keep both the amount of CO2 and the temperature constant.
Light intensity will decrease as the distance between the light source and the object increases, and vice versa.
Thus the relationship between LI and distance can be described as
1 This value will be very small; multiplying the LI 1000
LI = ---- by 1000 makes the LI a more 'workable' number. LI = ------
D2 D2
ie. Light intensity is inversely proportional to the square of the distance
Now, I must use this information to make a hypothesis and a plan for the experiment.
hypothesis
I believe that as the LI is increased, the rate of photosynthesis will increase fairly constantly as long as the other limiting factors of p/s are kept constant. This is because increasing the LI (unto the LSP) causes an increase of the rate of p/s, until the plant is photosynthesising as fast as it can, as long as changing the LI is the only variable of the experiment. If there are other variables at the same time as the varying light intensity, this will affect the rate of photosynthesis, and prevent the experiment from being a fair test.
planning
The apparatus used will be as follows:
Clamp stand etcϖ
Beaker (Water bath)ϖ
Boiling tubeϖ
0.5%ϖ Na+ HCO3- solution
ϖ Elodea Candensis specimen
Electric bench lamp with 100W filament bulbϖ
Thermometerϖ
Plasticene / Blu-Tac / Paperclipϖ
Stopwatchϖ
The apparatus will be set up as follows.
The water bath is used to keep the temperature constant - the water bath absorbs the heat from the lamp and thus prevents the Elodea specimen from photosynthesising at a faster rate due to temperature increase. The Na+HCO3- releases a constant supply of CO2 for p/s. The Elodea specimen is inverted so that the CO2 can be released more easily - the CO2 is released by the stomata which are on the underside of the leaf of the plant. Thus when the plant is inverted, the CO2 is not trapped beneath the plant's leaf, and is free to move. The Blu-Tac / Plasticene / paperclip is used to weigh down the Elodea specimen in the boiling tube.. This makes sure that the entire plant is submerged in the Na+HCO3- solution and therefore the entire plant is exposed to the CO2 released by the Na+HCO3-. However, this weight covers as few leaves as possible, thus reducing the chance that the CO2 production / release will be interfered with. Also, the weight must not cover the very tip of specimen, the meristem; this tip of the plant is where the plant is growing the most, and thus photosynthesising the most. The end of the plant should be cut at an angle, in order to release CO2 most effectively. The thermometer monitors the temperature of the water bath, thus checking whether or not there is a temperature increase or decrease, resulting in the change in the rate of p/s in the Elodea specimen. A change in the temperature would prevent the investigation from being a fair test. Hence, maintaining a constant temperature and CO2 level maintains a fair test, with only one variable changing - the LI. Counting the number of bubbles produced by the Elodea would be a fairly reliable way of measuring the CO2 produced. Obviously affixing a gas syringe to the top of the boiling tube would be far more reliable, but I doubt that there would be a sufficient volume of CO2 in a short time (max 3 mins) produced to make a considerable difference when reading the volume of gas produced by the Elodea specimen. By counting the number of bubbles, we are assured of a sufficiently large reading. The Elodea must be left for a sufficient amount of time for it to adjust to the new LI; I believe that five minutes should be ample enough - this will be consolidated by the preliminary results. Repeat readings must be taken to establish that there are no anomalous results - two extra readings should be sufficient (again the number will be determined by the preliminary results). The repeat readings will be taken after the original reading has been taken in the same manner as the original result. Anomalous results (if there are any) should be ascertained by the repeat readings.
In this experiment, there is little opportunity for accidents; however, the lamp will get somewhat hot during the experiment, and one must be careful not to burn oneself during the experiment. Also, utmost care must be taken, as ever, when working with glass apparatus, due to the risk of the shattering of the glass leading to injury.
The method will be as follows:
Set up apparatus as in diagramϖ
Leave the cutϖ Elodea for five minutes to adjust to the altered LI
Record the numbers of bubbles ofϖ CO2 produced in one minute
preliminary results
Using this setup and apparatus, I encountered the following problems:
9cm of Elodea did not fit into the boiling tube. Hence, the length of the specimen was reduced to 7cm, which did fit into the boiling tube. Five minutes was left for the Elodea to adjust to the LI. Then the number of bubbles of CO2 produced in a minute by the Elodea was measured. Two repeat readings were taken, and the three results averaged out. The averages are:
Distance / cm LI (1000?up>2) Bubbles / min Temp of water bath / ?c
5 40 immeasurable 26
10 10 immeasurable 25
15 4.444 (to 3dp) 46 22
…
35 0.816 (to 3dp) 16 22
40 0.625 9 22
45 0.494 (to 3 dp) ? 22
When the distances were less than 15cm, there were so many bubbles produced that it was impossible to count them, and also, the temperature was raised, thus preventing the experiment from being a fair test. However, at 15cm, it was possible to count the number of bubbles produced, and from this point onwards, the temperature remained constant. Ergo, I will take readings from 15cm onwards. Yet, when the distances were more than 40cm, there was only a maximum of one bubble produced every other minute (ie. ? a bubble per minute). 40cm.≥As this is less than 1, I have chosen to ignore readings of d
The 5 minutes adjustment time appears to have worked, as the readings are constant. Hence this time will be kept the same in the final experiment.
Consequently, I will change the following:
I will take measurements between 15cm and up to 40cm inclusive onlyϖ
I will use 7cm of Elodeaϖ
method
The apparatus was set up as in the planned diagram. The lamp was set fifteen centimetres from the Elodea specimen, and the specimen was allowed to adjust to the new light intensity for five minutes. Then amount of bubbles produced in one minute were counted. This was repeated twice, and the distance increased by five centimetres. The plant was left to adjust, readings taken and the distance changed up to 30 cm, this being the only number of measurements time allowed.
results
The followings results were obtained
Distance / cm LI (1000?up>2) Bubbles / min Temp of water bath / ?c Observations
56 22 22 Bubbles⎫15
4.444 63 22 22 produced⎬15
57 22 22 erratically⎭15
49 22 22 Steady⎫20
2.5 49 22 22 stream of⎬20
51 22 22 bubbles⎭20
33 22 22⎫25
1.6 37 22 22 None⎬25
40 22 22⎭25
22 22 22⎫30
1.111 24 22 22 None⎬30
21 22 22⎭30
Average - plot points
These results have been plotted on graph paper
analysis / conclusion
From the graphs we can see that as light intensity increases, the production of CO2 increases (and thus the rate of photosynthesis) unto the LSP (Light ≈Saturation Point). The graphs suggest that the LSP for Elodea is when the LI 4.5. Thus the distance at which the Elodea should reach its LSP is:
1000
LI = ---
d2
1000 ? √ d = ∴
֠(1000 ?5)∴ ≡ 15≈14.90711985
Thus, one could predict that at distances less than ~15 cm (and therefore light intensities greater than ~4.5) the number of bubbles of CO2 produced by an Elodea specimen would be approximately uniform.
When it comes to the slightly anomalous result shown on the LI vs. Bpm graph, there is a simple way to explain this; Elodea is a living organism, and no living organism follows a regimented pattern. Thus we can say that this anomaly is due to the specimen being not entirely infallible.
As I predicted, the rate of photosynthesis increased constantly unto the LSP because all limiting factors, other than light, were kept consistently the same. Thus these results support my prediction.
evaluation
I feel that this experiment has been successful in fulfilling the objective. The planned procedure worked fairly well, needing only a few minor adjustments to obtain good results. The evidence obtained supports photosynthetic theory and my prediction; it appears to be sound.
As mentioned before, the only (slightly) anomalous result is simple to explain; Elodea, being a living organism will not produce uniform results - thus the anomaly, it can be said, is due to the fallibility of the specimen.
No problems were encountered; the only circumstance which would have been a difficulty would have been controlling the temperature. However, this was eliminated by putting the boiling tube into a water bath which absorbed the majority of the heat energy from the lamp, and by keeping the specimen far away enough from the lamp for there to be no significant change in temperature.
This experiment is rather crude, and the method of measuring the rate of photosynthesis especially; counting the number of bubble of CO2 produced in a minute is not very accurate - measuring a volume would be far more precise, but the time for a reasonable amount of CO2 to be produced would be rather long, I feel; this would be inappropriate I believe, where time is limited.
Further work could be carried out, investigating the effects of the quality of light on the rate of photosynthesis; different coloured light for example could be used. This could be of commercial benefit, as finding out the effect of the colour of light on the rate of photosynthesis could aid plant growers to find out which type(s) of light make(s) plants grow quickest.
bibliography
Textbooks
Title Author Publishers
GCSE Biology (Second Edition) D. G. Mackean John Murray Publishers (Ltd.)
Biology (Nelson Science) Michael Roberts Thomas Nelson and Sons
Biology (Cambridge) Jones & Jones Cambridge University Press
Investigation into the factors that affect the rate of photosynthesis in Elodea
Introduction
Photosynthesis is the chemical process, which takes place in every green plant to produce food in the form of glucose. Plants use the suns energy to join together water and carbon molecules to make the glucose, which is sent around the plant to provide food. Cells in the root or stem can use the glucose to make energy, if the plant does not need to use all the glucose immediately then it is stored which is difficult because glucose is hard to store in water. Plants solve this problem by joining hundreds of glucose molecules together to make starch. Starch does not dissolve in water very well so it makes a better food store.
Photosynthesis takes place mainly in leaves and depends on an important green pigment called chlorophyll, which is found in chloroplasts. To obtain the most sunlight as possible, leaves have a large surface area and the more sunlight the plant receives, the better it can photosynthesize. Chloroplasts are found in palisade cells in large numbers and to allow as much light to get in as possible, the cells are arranged like a fence. This helps the energy entering the surface of the leaf to travel a long way through the palisade cells.
Glucose can provide energy or carbon, which can manufacture other molecules in the plant. Which can make new living matter and this is called biomass.
The chemical equation for photosynthesis is:
Carbon dioxide + Water = Glucose and Oxygen
6CO2 + 6H20 = C6H1206 + 6O2
Key Factors: CO2 is vital in photosynthesis because the plant takes in CO2 from the air and joins with water molecules to make glucose. The CO2 comes in through the stomata pores on the surface of the leaf and only 0.03 % of the air around is CO2 so it's pretty scarce.
Temperature has to be kept at a certain level because if it gets too hot, about 45`C then the enzymes in the chlorophyll will be killed and photosynthesis will stop altogether. If the temperature is too cold then temperature becomes a limiting factor and the enzymes will stop working.
Light As chlorophyll uses light energy to perform photosynthesis, it can only do it as fast as the light is arriving. Chlorophyll only absorbs the red and blue ends of the visible spectrum but not the green light in the middle, which is reflected back. If the light level is raised the rate of photosynthesis will increase steadily but only to a certain point.
Water is important because it is needed to join with CO2 molecules to make glucose and the amount of chlorophyll needs to be enough so that the plant can photosynthesize to the best of its abilities.
Investigation
Prediction
I predict that the plastic sheets coloured green, yellow and orange will produce the least amount of bubbles because the light will be transmitted. Whereas placing red and blue sheets in front of the Elodea will result in the greatest amount of bubbles because the light is absorbed. Certain colours of light can limit the rate of photosynthesis depending on how well it is absorbed into the plants chlorophyll to photosynthesize. Also the wavelength can change the rate of photosynthesis. If the lamp supplying heat for the plant were placed twice as far away, I predict that there would be half as many bubbles. Also if it were moved twice as far closer then there would be twice as many bubbles. This is backed up with knowledge from previous experiments and ones done by other people and scientific understanding.
Diagram
Previous experiment
Method
For our experiment we chose as accurate equipment as possible to give us the most accurate results. The equipment is as follows: 1 lamp
A boiling tube
A small piece of Elodea
Plastic sheets of different colours
A beaker
The boiling tube was filled with water and the Elodea placed in. The boiling tube was placed in the beaker and the lamp placed at a set length away. He plastic sheets were individually wrapped around the beaker with an elastic band. For every new plastic sheet we counted the number of bubbles each time for a minute. It was important to keep the experiment the same each time to ensure it was fair test for example: The lamp stayed the same distance from the beaker, we used the same plant each time and the plastic sheets were all the same size. The experiment was repeated three times and the results were averaged to ensure they were regular and as expected. Results were recorded each time and patterns observed. Previous results for an experiment of this kind have been recognized and compared. Throughout the experiment we made observations for a number of distinctive things:
? Increase/Decrease in bubbles
? Temperature Increase/Decrease
? Change in Elodea
? Size of bubbles
Variables include:
? Length of Elodea
? Amount of water
? Distance of lamp
? Size of boiling tube
? Transparency of sheets
? Time spent counting
Changing either of the variables would have had effects on the end results; we kept ours all the same each time to ensure a fair test.
Results
As predicted, the results conclude that using sheets with colours near the red and blue end of the spectrum produce a higher amount of bubbles than those near green. Thereby proving that photosynthesis is increased with certain colours of light.
Conclusion/Evaluation
In observation of the results, I have seen how the rate of photosynthesis in the Elodea has been affected by the various factors. In reference to the prediction, I was correct in that the red and blue coloured sheets produced the highest rate of photosynthesis, whereas the sheets, which were green and yellow, resulted in the least bubbles. I feel that we had taken enough measurements to be sure of a fair test as the experiment was repeated several times so. Each plastic coloured sheet we used had the same time, and variables as the others so we obtained precise results for every test. We did not find anything, which stood out too much from the pattern except that the red plastic sheet, when used resulted more bubbles generally than the blue sheet. This shows that chlorophyll absorbs red light more easily than blue. We acquired similar results with each repetition and found ours to be similar to previous experiments. The Elodea produced more bubbles with sheets at each end of the spectrum because the chlorophyll in the plant absorbs all the colours but transmits green. When the light is absorbed the plant converts it into energy to photosynthesize. The more light energy it receives the better and faster it can do this so when the sheets near the blue and red parts of the spectrum are held in front of the Elodea it absorbs the light and can photosynthesize better. If plastic sheets are held up which are have a colour near the green part of the spectrum then the light will be transmitted and the plant will not be able to photosynthesize as well. In this experiment we have covered the main colours of the visible spectrum and they are sufficient to produce the results that we are looking for.
If we were to repeat the experiment then there are several ways we could improve it. For example to get around the problem of the heat from the lamp producing more bubbles then a thick glass panel could be placed in the middle to prevent any heat reaching the Elodea. To improve the accuracy of counting the bubbles, you we could only count the ones, which are a certain size, and only the ones coming from the very end of the Elodea. If there were lots of people counting the bubbles and the results averaged then that would be a more accurate way of obtaining the information necessary. To extend the investigation you could change certain variables for example the type of plant that you are using to count the bubbles from. You could try an entire species of plant and see if the results are similar for every type. You could use different chemicals in the water each time to see which chemicals result in the greatest rate of photosynthesis.
