Investigating the effect of temperature on the rate of photosynthesis

Before starting my investigation on how temperature affects the rate of photosynthesis I carried out some research into photosynthesis. From this initial research I made a prediction based on the evidence that I found about the enzyme rubisco that is used in the dark stages of photosynthesis, and also on the limiting factors of light intensity, carbon dioxide concentration and temperature. I then went on to carrying out a preliminary experiment from which I learnt the factors that made the investigation inaccurate, therefore improving on them for my actual experiment.

During my actual experiment I used 7 different temperatures ranging from 0oC- 65oC.

The elodea was placed in these temperatures and a light shone on them for 5 minutes. The elodea was attached to a scale and syringe that was used to pull through oxygen bubbles so we could measure the rate of oxygen released and relate this to the rate of photosynthesis. I found that the rate of photosynthesis increased with temperature.

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The temperature peaked at 42oC, after this point the rate started to decrease. We collected a class average and did 3 T tests to compare 2 sets of results. The T test allows us to see whether the means of the sets of data differ significantly. I am 95% sure that there is a significant difference in my results between 0oC and 35oC, 0oC and 65oC, and 35oC and 65oC.

Aim: The aim of this experiment is to evaluate the effect of varying the temperature on the rate of photosynthesis. This will be done by measuring the rate of oxygen released from the olodea.

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In my experiment I will be measuring the volume of oxygen released from the elodea by shining a lamp to give the elodea light energy needed for photosynthesis to occur. I will repeat the experiment with the elodea in different temperatures to see the affect of this on photosynthesis. From the volume of oxygen released we will use this to predict the rate of photosynthesis.

Photosynthesis is the process by which plants that contain chlorophyll use sunlight to convert carbon dioxide and water into carbohydrates and oxygen. ( The trapped carbon dioxide is using the hydrogen from water to form the carbohydrate (commonly hexose sugars and starch). Here light energy is converted to chemical energy. The overall equation is written as:

There are two sets of reactions involved in photosynthesis. These are the light-dependant reactions, where light energy is needed, and light-independent reactions, where light energy is not needed. In our experiment the light energy source will be a lamp shining directly on the elodea. The light dependant reactions take place in the presence of suitable pigments that absorb certain wavelengths of light. Light energy is used to split water into hydrogen and oxygen. Oxygen is a waste product of the reaction. In our experiment we will measure the amount of oxygen released by pulling the oxygen bubbles released with a syringe and measure this using a scale. Light energy is also needed to provide chemical energy (ATP) for the reaction of carbon dioxide to carbohydrate in the light-independent reaction.

Photosynthetic pigments trap light energy. Different pigments absorb different wavelengths of light. The photosynthetic pigments of higher plants form two groups: chlorophylls and the carotenoids, each absorb different wavelengths of light so that the total amount of light absorbed is greater than if a single pigment were involved.

Chlorophyll absorbs light from the visible part of the electromagnetic spectrum. Chlorophyll is made up of different pigments: chlorophyll a, chlorophyll b, and chlorophyll c etc. mainly in the red (650- 700nm) and blue (400- 450nm) regions of the light spectrum as shown by the absorption spectrum graph and also the action spectrum. It absorbs least in the green region (550nm), which means it is mostly reflected, and why plants appear green.

The carotenoids absorb mainly in the blue-violet region of the spectrum.

The light energy that is absorbed excites electrons in the pigment molecules. When a solution of chlorophyll a or b is illuminated with ultraviolet light, a red fluorescence will appear. This is because the ultraviolet light absorbed excited the electrons. In a solution that contains only extracted pigment, the absorbed energy cannot usefully be passed on to do work and electrons return to their unexcited state and the absorbed energy is transferred to the surroundings as thermal energy and as light at a longer and less energetic wavelength than that which was absorbed, this is the red fluorescence. This is the energy that drives the process of photosynthesis in the system.

The light-dependant reactions of photosynthesis

These reactions occur in the grana, and include the synthesis of ATP in photophosphorylation and the splitting of water by photolysis to give hydrogen ions. The hydrogen ions combine with a carrier molecule NADP to make reduced NADP. ATP and reduced NADP are passed from the light-dependant to the light- independent reactions. The water in our experiment will be contained in the test tube the elodea is placed in, therefore it will be taken from here to be used in photosynthesis.

Photophosphorylation of ADP to ATP can be cyclic or non-cyclic depending on the pattern of electron flow in one or both photosystems.

Cyclic photophosphorylation:

This type of photophosphorylation involves only photosystem I. Light is absorbed by chlorophyll molecules in photosystem I and is passed to chlorophyll a (P700). An electron in the chlorophyll a molecule is excited to a higher energy level and is emitted from the chlorophyll molecule. Instead of falling back into the photosystem and losing its energy as fluorescence, it is captured by an electron acceptor and passed back to a chlorophyll a (P700) molecule via a chain of electron carriers. During this process enough energy is released to synthesise ATP from ADP and an inorganic phosphate group. The ATP then passes to the light-independent reactions. The electron is then returned to the photosystem to become stable

Non-cyclic photophosphorylation:

Non-cyclic photophosphorylation involves both photosystems involves both photosystems in the electron flow. Light is absorbed by both photosystems and excited electrons are emitted from the primary pigments of both reaction centres (P680 and P700). These electrons are absorbed by electrons acceptors and pass along chains of electron carriers leaving the photosystems positively charged. The P700 of photosystem I absorbs electrons from photosystem II. P680 receives replacement electrons from the splitting of water. As in cyclic photophosphorylation, ATP is synthesised by the ADP getting added to a phosphate group, as the electrons lose energy whilst passing along the carrier chain.

Photosystem II includes a water-splitting enzyme which catalyses the breakdown of water (photolysis):

Oxygen is a waste product of this process. The hydrogen ions combine with electrons from photosystem I and the carrier molecule NADP to give reduced NADP.

This passes to the light-independent reactions and is used in the synthesis of carbohydrate.

The light-independent reactions of photosynthesis

These series of reactions occur in the stroma. The fixation of carbon dioxide is a light-independent process in which carbon dioxide combines with a five-carbon sugar, ribulose bisphosphate (RuBP), to give two molecules of a three-carbon compound, glycerate 3-phosphate (GP). When carbon dioxide concentration is low less GP can be produced. The carbon dioxide in our experiment will come from the H20 from which it is dissolved. We will add sodium bicarbonate to increase the amount of carbon dioxide the elodea is exposed to, therefore will increase the rate of photosynthesis.

In the presence of ATP and reduced NADP, GP is reduced to triose phosphate (3-carbon sugar).

The enzyme ribulose bisphosphate carboxylase (rubisco) catalyses the combination of carbon dioxide and RuBP.

Some of these triose phosphates condense to form hexose phosphates, sucrose, starch and cellulose or are converted to acetylcoenzyme A to make amino acids and lipids. Others regenerate RuBP. This cycle is the Calvin cycle.

Factors affecting the rate of photosynthesis:

The main factors affecting the rate of photosynthesis are light intensity, temperature and carbon dioxide concentration.

As light intensity increases, the photosynthetic rate increases until a point is reached where the rate begins to level off. At low light intensity, photosynthesis occurs slowly because only a small quantity of ATP and NADPH is created by the light dependent reactions. As light intensity increases, more ATP and NADPH are created, thus increasing the photosynthetic rate. At high light intensity, photosynthetic rate levels out, due to other limiting factors, including competition between oxygen and carbon dioxide for the active site on RUBP carboxylase.


As this is a factor that affects the rate of photosynthesis, this could cause inaccuracies in my results if the light intensity is varied through my experiment. Therefore I will have to keep the light intensity that the elodea is exposed to equal for each experiment, in order for it to be a fair test. This will be done by measuring the distance of the lamp from the elodea on each experiment to keep the distance equal. I will also measure the light intensity using a light intensity meter

As carbon dioxide concentration increases, the rate of photosynthesis increases. At high concentrations, the rate of photosynthesis begins to level out due to factors not related to carbon dioxide concentration. One reason might be that some of the enzymes of photosynthesis are working at their maximum rate.

Carbon dioxide is found in low concentration in the atmosphere, and so atmospheric carbon dioxide levels may be a major limiting factor on photosynthesis when at low levels.


As this is a factor that affects the rate of photosynthesis, this could potentially cause inaccurate results in my experiment if different concentrations of carbon dioxide are exposed to the elodea.

As temperature increases above freezing, the rate of photosynthesis increases. This occurs because molecules are moving more quickly and there is a greater chance of a collision resulting in a chemical reaction. At some point, a temperature is reached that is an optimum temperature. The photosynthetic reaction rate is at its quickest rate at this point. Above that temperature, the enzymes begin to denature (as in RUBP carboxylase), slowing the rate of photosynthesis until a temperature is reached where photosynthesis does not occur at all.


Limiting factors:

At low light intensities, the limiting factor governing the rate of photosynthesis is the light intensity. As the light intensity increases so does the rate. But at high light intensities one or more other factors must be limiting, such as temperature or carbon dioxide supply.

At constant light intensities and temperature, the rate of photosynthesis initially increases with an increasing concentration of carbon dioxide, but again levels at higher concentrations. A graph of the rate of photosynthesis at different concentrations of carbon dioxide has the same shape as that for different light intensities. At low concentrations of carbon dioxide, the supply of carbon dioxide is the rate-limiting factor. At higher concentrations of carbon dioxide, other factors are rate limiting, such as light intensity or temperature.


I predict that when the elodea is placed in water with a temperature of 0oC, there rate of photosynthesis will be at a minimum. I predict that few if any oxygen bubbles will be produced. This is because the enzyme RUBISCO works best at higher temperatures as they gain more kinetic energy, therefore binding with active sites at a faster rate. The active site is the specific region of the enzyme that combines with the substrate. The active site has a specific shape that fits uniquely to the geometric shape of the substrate. This is the lock and key theory that only a certain substrate (key) can fit into a certain active site (or key hole) in the enzyme(lock).

At 0oC the enzyme has little kinetic energy, and as the dark stage of photosynthesis is controlled by enzymes; RUBISCO catalyses the combination of carbon dioxide and RuBp, this will be done slower than at a higher temperature. Therefore the whole calvin cycle will be completed at a slower rate.

When the elodea is in water with a temperature of 15oC I predict the rate of photosynthesis will increase from when it was in 0oc. This is because the dark stage is controlled by the enzyme rubisco, which catalyses carbon dioxide and RuBP. Enzymes work best at warm temperatures, as they have more kinetic energy therefore colliding with active sites at a faster rate. Therefore I predict the elodea will produce more oxygen bubbles at 15oC. Learn what is the optimum concentration of pectinase

When the elodea is placed in a water bath of 35oC, I predict the rate of photosynthesis will increase further; this is because the enzyme rubisco is working nearer to its optimum rate. This is the temperature at which enzymes work at their maximum rate. The optimum temperature for enzymes in plants is around 40oC. Therefore I predict more oxygen bubbles will be produced at this temperature.

When the elodea is placed in a water bath of 65oC, I predict the rate of photosynthesis will decrease steeply. This is because enzymes control the dark stage of photosynthesis. Enzymes get denatured after the optimum temperature (40oC), as its three-dimensional shape changes and intra and intermolecular bonds are broken, so that the enzyme and substrate cannot be held in place long enough to react, and because of the shapes changing they also do not bind as specifically as before. Therefore I predict after the optimum temperature the rate of photosynthesis will decrease, releasing a smaller volume of oxygen.



1. Fill less that half the beaker with water, at room temperature.

2. Place the elodea in a test tube and fill with water to the top.

3. Make sure the elodea is at the top of the test tube and place it upside down in the beaker of water, keeping the test tube filled with as much water as possible. Water level must be higher than elodea in order to count carbon dioxide bubbles.

4. Place light directly shining on the test tube and beaker, and leave to acclimatise for one minute. Use a stop clock to time this.

5. After it has acclimatised, reset the stop clock and start the time again.

6. Count the bubbles released from the elodea for 5 minutes. Check stopwatch regularly so that time does not overrun.

7. Note down results in results table.

8. Repeat this experiment in a beaker of ice water (0oC), and at temperatures of 30oC and 40oC.


Number of bubbles released after 5 minutes

Temperature (oC)

Number of bubbles released










During our preliminary experiment, many errors occurred which would affect the accuracy and results of the experiment. Changing the following will do this:

The room the experiment was carried out in was not dark enough, therefore light intensity is affected and cannot be controlled. Therefore in our actual experiment the windows will be blacked out so that the elodea get light only from the lamp and use a light intensity meter.

We did not measure the distance from the lamp to the experiment, therefore light intensity may have been different, making the experiment unfair and could lead to inaccuracies. In the actual experiment I will keep the distance between the lamp and experiment constant.

It was difficult to keep the temperature of the water constant, to do this we had to add ice/water to keep the temperature constant. However this wasn’t very accurate. Therefore in our actual experiment we will use a water bath, as this will keep the temperature constant. We could also use a heat shield.

In our preliminary experiment we left the elodea to acclimatise for 1 minute. This may not have been enough time for the experiment to be accurate. Therefore in our actual experiment we will leave it to acclimatise for 5 minutes.

The experiments took place at different times of the day, therefore there would have been different light intensities for different experiments, which would cause inaccuracies in our results. This shows it was not a fair test. For our actual experiment the room will be blacked out, therefore the light from outside will not affect the experiment.

In our preliminary experiment we measured the rate of photosynthesis by counting the amount of oxygen bubbles released. This was not very accurate as bubbles could have been missed. Therefore instead of counting bubbles we will pull through all oxygen bubbles after the time is finished. Therefore all bubbles will be together and give a more accurate reading as bubbles will not be missed.

The rate of photosynthesis is measured by oxygen released. However in our preliminary we did this by counting bubbles. However this is also inaccurate as bubbles are all of different sizes, therefore volume is not measured accurately. In our actual experiment we will use a scale. This measures the volume of the bubbles, therefore will be more accurate to measure rate.

In our experiment we did two repeats. This is not enough repeats to make the results reliable. Therefore in our actual experiment we will do at least three repeats. If results are not similar to each other, then more results will be obtained, in order for a more accurate and reliable average.

We only experimented with four different temperature variations. This is not enough to get an accurate idea of how temperature affects photosynthesis. Therefore in our actual experiment we will do at least ten different temperatures, in order to make the results more reliable. Therefore we can get a better idea of how temperature affects the rate of photosynthesis.






So that photosynthesis can be carried out, light is compulsory.

Test tube


To contain the elodea



To contain the test tube, and water of different temperatures.

Water tub


Larger volume of water than a beaker, therefore changing temperature less easily.

Thermometer (accurate to 1oC)


To make sure the water is of the correct temperature.

Light intensity meter (1-10) (not very accurate as lever fluctuates)


To check whether light intensity is the same in all experiments, therefore making sure it’s a fair test.

Plastic tube


To attach to the syringe and scale, in order for bubbles to be pulled through.



To pull oxygen bubbles through.



To measure to volume of oxygen released.

Ice cubes


To decrease temperature until wanted temperature is gained.

Boiling water


To increase the temperature until wanted temperature is gained.

Water bath


Large volume, therefore temperature of water changes less quick, maintaining the desired temperature,

Clamp and stand


To hold up and support the scale and also the test tube if it is placed in the water bath.

Ruler (accurate to a millimetre)


To measure the distance from the lamp to the elodea, therefore light intensity will be more even.



To test the rate of photosynthesis for different temperatures.

Elodea water


Will be in the test tube, and contain the elodea.

Sodium bicarbonate


To increase rate of photosynthesis if not occurring.


1. Cover the windows and doors in black paper. This is so no light gets through and affects our experiment, which can cause inaccurate results.

2. We started our experiment with a temperature of 15oC. We will get a water tub and fill it with water from the tap. Start with tap water, as the temperature of this would be nearest to 15oC.

3. Measure the temperature with a thermometer. If the temperature is a little higher than 15 degrees then we will add some ice cubes into the water tub to lower the temperature. When exactly 15 degrees is reached, we will remove the ice cubes. If they were left to melt further, the temperature would drop to under the desired temperature. If the temperature is slightly lower than 15 degrees we will add minuet amounts of warm water until exactly 15 degrees is reached. We used thermometers to measure temperature, as it is relatively accurate, to the nearest degree.

4. Set up experiment as shown in the diagram, and hold the scale and syringe using a stand and clamp.

5. We will cut the elodea to exactly 7 cm at a slant. The elodea is cut at a slant, as less air bubbles will be trapped. Note down length of elodea so that it will be kept the same for each experiment.

6. Using a syringe, place some elodea water in the test tube along with the elodea.

7. Hold test tube up with stand and clamp, and hold elodea upside down by putting it inside the tubing. Pull through any bubbles before starting the experiment. This is done so that no excess bubbles are already there, which will make the experiment inaccurate.

8. Measure with a ruler the distance the lamp is away from the elodea. This is so that the lamp is an equal length away from the elodea at all times in order for it to be a fair test.

9. The light intensity will be measured with a light intensity meter. This will need to be the same for every experiment. This is because light intensity affects the rate of photosynthesis, therefore needs to be kept equal throughout. This however is not very accurate as the meter constantly fluctuates.

10. When experiment is set up correctly, start the stop clock for 1 minute. This is so the elodea can acclimatise.

11. When the elodea has acclimatised for 1 minute, set the stop clock again, and leave for 5 minutes. Watch the stop clock well, so that the time dos not overrun.

12. Make sure temperature does not change from 15 degrees, if it does, add ice or warm water to make it to the exact temperature. The temperature needs to be monitored as it can change during the course of the experiment as it can vary slightly, causing inaccuracies in the results.

13. Straight after stopping the stop clock, we will slowly pull through the oxygen bubbles, with the syringe. This has to be done slowly as the bubbles come through fast, therefore if not careful it can go straight to the syringe, therefore the bubbles cannot be measured.

14. Pull the bubbles so that they line up with the scale, note down the volume of oxygen released.

15. At the experiment of 0oC, set up apparatus as before, only using a beaker instead of a water tub. A beaker is used instead, as 0 degrees is hard to reach, therefore if is easier to decrease the temperature more dramatically in a smaller volume of water.

16. Use the same equipment in all experiments. This is so that it is a fair test, and results will be more accurate.

17. Repeat procedure, and note down volume of oxygen produced.

18. For temperatures of 35oC, 45oC, 55oC and 65oC, a water bath is used instead of a beaker or water tub. This holds the largest volume of water and temperature is controlled electronically. This makes the temperature more accurate as less likely the temperature will fluctuate.



During our experiment we need to take precautions to carry out our experiment as safely as possible. For this we need to:

Wear safety goggles- this is because we are working with water, and in some experiments the water will be hot. If water is accidentally splashed in our eyes it can be very serious, therefore goggles need to be worn to prevent this.

Be careful not to slip, therefore walk and not run in the class. This is because water can easily be spilt in during the experiment, therefore a chance it will be on the floor, making it a hazard.

The water bath needs to be plugged in to electronically keep the temperature accurate. Therefore we will need to be careful not to get water near the plug points, as their could be a risk of an electric shock.

Key Variables

During my experiment I will vary one factor, this factor will be temperature. The temperature of the water will be changed for all experiments, this will be what we will measure. We will also change the water baths. In some experiments we will use a beaker, some a water tub and some a water bath. This is because of how efficient it is for that particular temperature.

The factors we will keep the same in order to make the experiment accurate are: the length of the elodea for each temperature. This will be 7cm each time. This will be because a longer elodea may mean more leaves, which provides a larger surface area in total, allowing more light to be absorbed, therefore increasing the rate of photosynthesis. The time to allow the elodea to photosynthesis will be kept the same; this will be 5 minutes and will be measured using a digital stop clock, as this is more accurate than a non-digital stop clock. We will try to keep the amount of sodium bicarbonate the same, at 2g that will b measured using scales. It will be added to the water by a spatula. The amount of spatulas of sodium bicarbonate will be kept equal throughout all experiments.

The light intensity will be kept the same, by keeping the lamp an equal distance from the elodea in each experiment. This will be done by measuring the distance between these using a ruler (correct to 1mm), and also using a light intensity meter.


Table of results showing the average rate of oxygen produced at different temperatures



Length of bubble in 5 minutes (mm)

Volume of oxygen made in 5mm (mm3/ 5mins)

Rate of oxygen produced per min (mm3/ min)

Average rate of oxygen produced (mm3/ min)

LUX (light intensity value) 1-10




0 R

0 R2















15 R

15 R2















25 R

25 R2















35 R

35 R2















45 R

45 R2















55 R

55 R2















65 R

65 R2














Class results

Average rates of photosynthesis for each group (mm3/min)

Temp (oC)














Avg rate of p/s (mm3/min)











































































































Statistics: T-Test

A t-test allows you to see whether the means of sets of data differ significantly. Therefore we will do 3 t-tests on 2 sets of class results to determine whether these figures vary greatly.

We first thing we do is calculate the mean. To do this the values in each set will need to be added and divided by the total number of measurements. The general formula is:

At 0oC:

Mean: 2.38 = 0.1830769231


With the mean, we can now calculate the standard deviation. The standard deviation is a measure of the extent to which individual measurements vary around the mean. The greater the variation among the individual measurements, the bigger the standard deviation; the less the variation among the individual measurements, the smaller the standard deviation.

The standard deviation, Sx, is given by the following formula:


Sx = ?x2 – n


?x2 = (0.42 + 0.102 + 0.072 + 0.102 + 0.132 + 0.082 + 0.102 + 0.102 + 0.102 + 0.402 + 0.132 + 0.272 + 0.402)

= 0.648

(?x)2 = (0.4+ 0.1+ 0.07+ 0.1+ 0.13+ 0.08+ 0.1+ 0.1+ 0.1+ 0.4+ 0.13+ 0.27 +0.4)2

n 13

= (2.38)2


Sx = 0.648- (2.38)2



= 0.648 – 0.4357


= 0.1330027954

At 35oC:

Mean :

445.55 = 34.27307692


Standard deviation for 35oC:

?x2 = 16820.3291

(?x)2 = (445.55)2

n 13

= 15963.52327

16820.3291 – 15270.36942

Sx = 12

= 129.1633067

= 11.36500358

At 65oC:

Mean: 64.08 = 4.929230769


Standard deviation at 65oC:

?x2 = 649.8602

(?x)2 = 64.082

n 13

= 315.8651077

Sx = 649.8602 – 315.8651077


Sx = 27.83292436

Sx = 5.275691837

We will now use the standard deviations to calculate the significance of the difference between two means.

T- test of 0oC and 35oC

1. Work out the means of the two sets of data:

0oC = 0.1830769231

35oC = 34.27307692

2. Subtract the smaller mean from the larger one.

34.27307692 – 0.1830769231

= 34.09

3. Work out the standard deviation of one set of data and square it. Divide by the number of pieces of data in that set of data.

For 0oC:



= 1.360749506 x 10-3

4. Complete step 3, for the second set of data.

For 35oC:



= 9.935638952

5. Add together the figures from 3 & 4.

1.360749506 x 10-3 + 9.935638952

= 9.936999701

6. Find the square root of this figure.

= 3.1523007

7. Divide the figure in step 2 by the figure calculated in step 6. This is the t value.

34.09 I


= 10.81432365

8. Use the table to see whether your value of t could be expected by chance. For the t- test, the degrees of freedom are simply 2 less that the total number of individual measurements in the two samples.

Degrees of freedom: (13 x 2) – 2 = 24

T value = 2.06

Since the value of t is bigger than the critical value -the one that corresponds to a 5% probability that chance could have produced it- in the table I can be at least 95% confident that the difference between the means is significant.

T- test for 35oC and 65oC

1. Mean volume of oxygen released at 35oC = 34.27307692.

Mean volume of oxygen released at 65oC = 4.929230769.

2. Difference between means = 29.34384615.

3. Standard deviation of the volume of oxygen released at 35oC squared, divided by number of pieces of data = (11.36500358)2 = 9.935638952


4. Standard deviation of the volume of oxygen released at 65oC squared, divided by number of pieces of date = (27.83292436 )2 = 2.120994181


5. The sum of the figures calculated in steps 3 and 4 =

9.935638952 + 2.140994181 = 12.07663313

6. The square root of the figure calculated in step 5 = 3.475145052

7. The difference between the two means (step 2) divided by the figure calculated in step 6 = 29.34384615 = 8.443919812.


8. 8.44 is greater than the critical value of t, which for of 24 degrees of freedom equals 2.06. This means that we are at least 95% confident that the mean volume of oxygen released at 35oC and 65oC differs.

T- test for 0oC and 65oC

1. Mean volume of oxygen released at OoC = 0.1830769231.

Mean volume of oxygen released at 65oC = 4.929230769.

2. Difference between means = 4.746153846

3. Standard deviation of the volume of oxygen released at 0oC squared, divided by number of pieces of data

= (0.1330027954)2 = 1.360749506 x 10-3


4. Standard deviation of the volume of oxygen released at 65oC squared, divided by number of pieces of date

= (27.83292436 )2 = 2.120994181


5. The sum of the figures calculated in steps 3 and 4 =

1.360749506 x 10-3 + 2.120994181= 2.122354931.

6. The square root of the figure calculated in step 5 = 1.45683044.

7. The difference between the two means (step 2) divided by the figure calculated in step 6 = 4.746153846 = 3.257862903.


8. 3.26 is greater than the critical value of t, which for of 24 degrees of freedom equals 2.06.

The critical value of the table at 5% confidence is 2.06.

My t value is bigger than the value from the table therefore I am 95% confident that there is a significance difference in the results between the two temperatures.

By looking at my graph of average results from the class, the best fit curve starts to increase slowly from 0oC to 15oC, where is goes from 0.4mm3/min to 6mm3/min. This is an increase of 5.6mm3/min in a range of 15 degrees. Over the next 15 degrees, as the temperature increases from 15 degrees to 30 degrees, the volume of oxygen goes from 6mm3/min to 28.4mm3/min. This is an increase of 22.4mm3/min, which shows the volume of oxygen increases more rapidly as the temperature increases. The shape of the graph shows this as steepness of the best-fit curve increases till around 25oC. This is the same pattern for graph 1, as after 25 degrees the curve of best fit increases steadily. After around 25 degrees the line increases steadily till around 32 degrees on graph 2, and the same on graph 1, where after the steepness of the curve starts to decrease. The curve peeks at around 42oC where the elodea releases an average rate of 41.2mm3/min of oxygen on graph 2. On graph 1 the curve of best fit peeks at around 42 degrees as well but with a rate of 35.4mm3/min. After this temperature the best-fit curve decreases as steeply as it increased before it peeked. At 50oC, on graph 2, the average rate of oxygen released is 35mm3/min and at 65oC the rate of oxygen released is 5.6mm3/min. The difference between these results with a range of 15 degrees is 29.4mm3/min.


By looking at the class average graph and our group graph they both follow the same trend. On graph 1 (group average) the curve increases rapidly from 0oC to around 22oC, where the average rate of oxygen released rises from 0.6mm3/min to 12mm3/min. This large increase occurs between 0oC and 24oC on graph 2 (class average). The average rate of oxygen released rose from 0.4mm3/min to 17mm3/min. This happens because as the temperature starts to increase, the enzyme rubisco gains more kinetic energy. This enzyme is needed in the dark stage of photosynthesis to catalyse the conversion of ribulose bisphosphate and carbon dioxide into gycerate 3-phosphate in the Calvin cycle.

The enzyme works as its active site, which is a specific part of the enzyme that reacts, binds to a substrate molecule. The substrate and active site have a specific 3-D shape that fit together in a ‘lock and key’ form, so that only a particular active site and substrate can combine and react.

The substrate is then released forming a product, which in this case is GP. As the temperature increased from 0oC to 22oC on graph 1, and 0oC to 24oC on graph 2, the enzymes gain more kinetic energy, therefore colliding and binding with the substrate at a faster rate and also with more energy. This will cause reactions to speed up, hence the graph increases rapidly. I correctly predicted the rate of oxygen produced would rise, as temperatures get warmer, due to the increased kinetic energy of the enzyme rubisco.

The line of best-fit increases steadily from 22oC and 35oC on graph 1, where the average rate of oxygen released went from 12mm3/min to 30.8mm3/min. It increased steadily from 24oC to 33oC on graph 2, where the average rate of oxygen released goes from 17mm3/min to 34.1mm3/min. This is because as the temperature increases the kinetic energy the enzyme rubisco has will also increase. Making the substrate bind to the active site of the enzyme at a faster pace, increasing the rate of reaction. Therefore rubisco will catalyse carbon dioxide and ribulose bisphosphate to GP faster as temperature increases. The curve increases steadily during these temperatures as the enzymes and substrate acclimatise to the gradual rise in temperature. I correctly predicted that at 35oC the temperature would increase further as the kinetic energy rubisco has increases.

The graph peaks at 44oC on graph 1, where the average rate of oxygen released is 35.2mm3/min. On graph 2 the curve of best-fit peaks at 43oC, where the average rate of oxygen released is 41.2mm3/min. This is the enzyme rubisco’s optimum temperature, meaning the temperature where the enzyme works at its maximum rate. This is where the enzymes have the maximum amount of kinetic energy, therefore the active site and substrate will collide more, with more energy forming the product GP at the fastest possible rate. My prediction was close to my results, as I predicted the optimum temperature would be 40oC, although this is slightly lower that the results I obtained, it is still relatively near to 44oC and 43oC.

Above the optimum temperature the rate decreases as more and more of the enzyme molecules denature. The thermal energy breaks the hydrogen bonds holding the secondary and tertiary structure of the enzyme together, so the enzyme (and especially the active site) loses its shape to become a random coil. The substrate can no longer bind, and the reaction is no longer catalysed. At very high temperatures this is irreversible. Only the weak hydrogen bonds are broken at these mild temperatures.

The graphs starts to decrease after 44oC for graph 1, and 43oC for graph 2. Graph 1 rapidly decreases from 44oC to 75oC where the average rate of oxygen decreases from 35.2mm3/min to 0mm3/min. Graph 2 begins to decrease from 43oC to 75oC where the average rate of oxygen released goes from 41.2mm3/min to 0.4mm3/min. This is because as temperature increases above optimum temperature, more bonds break, and the 3D shape changes further, making it less likely for the enzyme and substrate to bind, as the lock and key theory will no longer work. When GP cannot be made the Calvin cycle cannot be completed, therefore the dark stage of photosynthesis cannot occur, releasing less and less oxygen.

My graphs for both my group and the class average generally follow this pattern; therefore I correctly predicted the effect of temperature on the rate of photosynthesis.


Anomalous results:

During my experiment I got one anomalous result (graph1), which was a considerable distance from the trend curve. This was the rate of oxygen released at 25oC, the average rate of oxygen released for this temperature was 6mm3/min. For it to fit exactly on the best-fit curve the average rate of oxygen should be 15.4mm3/min. On the class average graph (graph 2), there is also one anomalous result. This is the result for 35oC with an average rate of oxygen released of 34.27. To fit the trend line exactly, the average rate of oxygen released should be around 37mm3/min.

There are many possible reasons that could result in these anomalous results. Human error could have affected them, this is because the elodea was changed in between the days. This could have a drastic affect on the results as even thought the length of it was the same on both occasions, the number of leaves could have been different, the surface area of the leaves could vary and the amount of chlorophyll on both elodea could be different, therefore absorbing different amounts of light, affecting the rate of photosynthesis. The light intensity varied between 6 and 7 on the light intensity meter, even thought this is not a big difference it could still be significant enough to cause inaccuracies in the results. The light intensity meter was not digital and was constantly fluctuating, therefore exact readings were not possible. Other human errors could be the measurement of the volume of oxygen against the scale. This is because on many occasions the bubbles did not show as one continuous bubble, but in fact many small ones. Therefore we had to add these up separately, this could have been done inaccurately, and as the scale was against graph paper, it is difficult to get an exact reading. The temperature of the water could be inaccurate; where the water was not monitored electronically the temperature could fluctuate. Adding ice and warm water is not an accurate way to keep the temperature constant. This could have caused the enzymes to work at different speeds, causing the rate of photosynthesis to alter.


We could not fully control the light intensity, as even thought the room was blacked out to ensure no excess light contributed to the experiment, there were many other experiments occurring in the same room, therefore many other lamps. This means that light from lamps other than ours could have affected our experiment, as it means the chlorophyll received a higher intensity than was intended, therefore increasing the rate of photosynthesis. The light intensity meters were not digital, therefore did not give a definite reading. The meter was constantly fluctuating therefore it is not completely certain how constant light intensity was in each experiment.

The elodea was changed between days; this could have made a big difference to our results. This is because both elodeas will most likely have a different number of leaves, and also the leaves will have different surface areas. This means there will be different numbers of chlorophyll on each, therefore light absorption will vary between elodea, meaning different rates of photosynthesis and different amount of oxygen released as a result of this.

The distance of the lamps from the elodea was measured by only a ruler. This was very inaccurate, as the curvature of the lamp was different, therefore affecting the height of it also. As some of the experiments took place in a water bath, the lamp had to be held higher than it otherwise would, therefore shining on a different part of the elodea, this could be a part where there are more or less leaves, affecting the rate of photosynthesis. Also if light is shining from the top, the bottom leaves will be shielded from this light, which in other experiments will more often not.

The temperature of the water may not have been completely accurate. This is because during the 5 minutes the elodea was left, the temperature often drifted from what was needed. In this case, we added ice or warm water to allow the temperature to return to the desired. This is not a very accurate way to keep the temperature level. The temperature in the electronic water baths, were sometimes not on the temperature programmed, therefore we had to change it with ice and warm water also.

Sodium carbonate was added to speed up the rate of photosynthesis; the amount of this however was not measured. Therefore this will mean the rate of photosynthesis was sped up by different amounts, causing the oxygen bubbles to be released at different rates than it might have, if sodium bicarbonate levels were the same.

During the experiment, the whole of the elodea was not emerged in water. This is because the top of it had to attach to the tube. This means that not all the oxygen bubbles released could be counted, as it would be released into the atmosphere rather than the water.

Significant Limitation:

The most significant limitation is that we cannot fully associate the rate of photosynthesis with the amount of oxygen released by the elodea. This is because some of the oxygen in the elodea is used to allow the plant to respire. Respiration releases energy, of which is needed in photosynthesis. This means the oxygen released is only part of the oxygen produced by the plant, as some has already been used up.


I believe my results were quite accurate. This is because most results are close to the trend line, and both graphs follow the same pattern. However, some of the equipment we used was not as accurate as it could have been.

The light intensity meter was not digital, and the arm fluctuated constantly, therefore not giving an accurate reading of the light intensity. This piece of equipment was the least accurate in our experiment.

The temperatures of the water often varied, therefore we had to add ice and warm water. This was not very accurate; therefore all experiments should be carried out in a water bath, which will electronically keep the temperature constant. However in some water baths, even though the temperature was set, when we checked with the thermometer, it wasn’t that temperature exactly. Therefore even the water bath is not completely accurate.

The distance of lamp to the experiment was not kept as constant as it could have. This is because the distance was measured by a ruler, and is only accurate to the nearest mm. Also the distance was only measured and not the height of the lamp compared to the elodea.

The thermometer was not as accurate as it could have been, as it was only accurate to 1oC. Therefore this is the closest we could measure the temperature to. Also as it is thin, it is hard to measure with the human eye exactly the temperature desired, which can cause inaccuracies.

The syringe pulls the bubbles through fast; therefore we need to pull very slowly to align the bubbles correctly with the graph paper beneath. This was often done inaccurately, as the graph paper is only correct to a mm. Also there usually is more than one bubble, therefore they all need to be added. This could make it inaccurate, as each measurement is accurate to the nearest mm.


During my experiment, we did 2 repeats for each temperature. For the temperature of 0oC, the maximum difference between the three results for rate of oxygen produced per minute is 0.4mm3/min. This is a small difference, therefore the set of results for 0 degrees is very accurate. For 15 degrees the maximum difference in rate of oxygen between the 3 results is 0.8mm3/min. This is a relatively small difference, although not as minor as for 0 degrees, it is still accurate. For the temperature of 25oC the rate of oxygen released from the 3 sets of results has a maximum difference of 0.4mm3/min. This is a very small difference, therefore the results for 25 degrees is very reliable. For the temperature of 35oC the maximum difference between the results for the rate of oxygen released is 6.44mm3/min. This is a significant difference, therefore the results for 35 degrees is largely inaccurate. For 45oC the maximum difference between the results is 4.42mm3/min. This is a big difference; therefore the results for 45 degrees are unreliable. For the temperature of 55oC, the maximum difference between the 3 sets of results for rate of oxygen released is 1.21mm3/min. This is quite a significant difference therefore the results for 55 degrees were slightly inaccurate. For the results for 65 degrees the maximum difference for the set of 3 results is 1.24mm3/min. This is also slightly inaccurate as there is a significant difference.

Errors and their effects:

Errors that could have been made during our experiment were:

* The bubbles could be pulled through too fast, therefore going into the syringe, causing inaccuracies when being pushed back out. This will cause our measurements to be wrong when we are reading off the scale. Also as there were often many small bubbles, which we had to add together to get one reading, this was often done inaccurately because it is hard to measure the size of small bubbles.

* The timing was another inaccuracy. This is due to human error, as the clock was not stopped at exactly 5 minutes. Also after the clock was stopped, different times were taken to pull the bubbles through, therefore allowing photosynthesis to occur a few moments longer. This could affect the results in that there was less photosynthesis taking place than our results show. Read the answer what is the optimum concentration of pectinase

* The amount of sodium bicarbonate added to the experiment is different in each experiment, as the amounts were not measured. This means that the rate of photosynthesis will be at different rates in all experiments, releasing oxygen at rates that are inaccurate.

* The temperature was rarely kept completely constant during the experiment. Therefore we had to always add ice, and warm water to the water bath. This was very inaccurate as even small amounts of warm water affect the temperature by a large amount. This means if the temperature goes higher than needed, ice needs to be added. It takes long for the ice to melt and for it to affect the temperature. The time taken for the correct temperature to be reached could affect the results and cause inaccuracies, which could make the volume of oxygen released more or less than it otherwise would be


The first improvement I could make to my coursework if I had to repeat it is measure the mass of sodium bicarbonate being put into each experiment. Making sure that each experiment gets the same mass in order for the results to be accurate.

I would also use a water bath for all experiments, and not just some. This will mean that the temperature in all experiments will stay constant, as adding ice and warm water is not accurate.

A data logger will be a lot more accurate way of measuring fluctuations in temperature. A data logger is an electronic instrument that records measurements (temperature, relative humidity, light intensity, on/off, open/closed, voltage, pressure and events) over time. Temperature is measured in my experiment. Typically, data loggers are small, battery-powered devices that are equipped with a microprocessor, data storage and sensor. Most data loggers use turn-key software on a personal computer to start the logger and view the collected data. First, the data logger is connected to a personal computer. Then the turn-key software is used to select logging parameters (sampling intervals, start time, etc.) and initiate the logger. The logger is then disconnected and deployed in the desired location. The logger records each measurement and stores it in memory along with the time and date. The logger is then reconnected to the personal computer and the software is used again to readout the data and see the measurements as a graph, showing the profile over time, this will allow us to see any fluctuations that may occur.

A digital light intensity meter should be used instead of analogue; this is so the light intensity can be measured in exact figures. Therefore on all experiments, the elodea can receive the same light intensity, allowing the experiment to be more accurate and fair.

We could also experiment with more temperatures, this will allow our results to be more accurate, as they would be tested more and a clearer trend can be seen. These temperatures will all be between 0oC and 70oC.

I would also do more repeats, if I could do the experiment again. As I have shown, the reliability of some results is low; therefore I would do more repeats for these results in particular. This will make the results more reliable.

We should also use the exact same equipment for each temperature e.g. same elodea. This is necessary as it can cause inaccurate results due to different number of leaves the different elodea contain. This will affect the rate of photosynthesis, as each will have a different total surface area, therefore absorbing different amounts of light. Other equipment will also need to be kept the same so that all results will be reliable.

Cite this page

Investigating the effect of temperature on the rate of photosynthesis. (2021, Jun 02). Retrieved from

Investigating the effect of temperature on the rate of photosynthesis

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