Factors that Affect the Rate of Photosynthesis Aim: To investigate a factor that affects the rate of photosynthesis.
Outline: A piece of pondweed will be cut and placed into a beaker
containing water and sodium hydrogen carbonate. A lamp will be shined
on to the pondweed and the amount of bubbles released from the plant
will be counted. The lamp will be adjusted to different distances from
the plant to try and obtain different results.
6CO2 + 6H2O light energy & chlorophyll C6H12O6 + 6O2
Experimental Variable- Light intensity is to be the variable explored
in this investigation. Increasing or decreasing the distance from the
to the plant can vary light intensity.
Light Wavelength (color)- Light energy is absorbed by pigments in the
leaf such as chlorophyll. Chlorophyll easily absorbs blue light, in
the 400-450 nm range, and also easily absorbs red light in the 650-700
nm range. Chlorophyll does not absorb green light
or yellow light
effectively but tends to reflect them, decreasing the amount of light
absorbed and decreasing the rate of photosynthesis
. Why the rate of
photosynthesis increases or decreased from the amount of light energy
absorbed is what is being investigated in this experiment. The light
color can be fixed by using the same lamp throughout the experiment.
Carbon Dioxide- CO2 concentration can affect the rate of
photosynthesis since the more CO2 in the air, the more CO2 that can
diffuse into the leaf. This variable can be fixed by adding a fixed
amount of sodium hydrogen carbonate to the beaker and plant. The
experiment should also be completed in one session and under two hours
so the plant does not use up a significant percentage of the CO2.
Water- Water is required in the photosynthetic reaction. When plants
lack water, their stomata close to prevent further water loss. At the
same time, closing the stomata cells doesn't allow CO2 to diffuse into
the leaf. Water is also therefore, linked to the carbon dioxide
factor. Water can be kept a constant by keeping the same amount of
water in the beaker.
Temperature- Enzymes are used in photosynthesis and the respiration of
the plant. Therefore, increasing the temperature will increase enzyme
reaction and the photosynthetic rate until a certain point is reached
when the enzymes denature. The temperature can be kept somewhat a
constant by performing the experiment in one session, when the air
temperature shouldn't change enough to affect water temperature. A
transparent glass block will also be placed in front of the lamp to
retain some of the heat from the lamp.
Plant- Different species plants have different photosynthetic rates
due to the different leaf structures of the plants. Even plants of the
same species may have slightly different rates of photosynthesis since
there may be more or less chlorophyll in the leaves to absorb light.
The size of the plant is also important since this would affect the
amount of surface area for gas exchange. The only solution to
controlling this variable is by using the same plant throughout the
Limiting Factors- Light, carbon dioxide, temperature, and chlorophyll
are all limiting factors, meaning that even when there is surplus of
every other variable, the rate of photosynthesis will be limited by
the limiting factor until there is an optimal amount of the limiting
factor to increase the rate of photosynthesis further. Otherwise, the
rate of photosynthesis can no longer increase.
Prediction: I predict that increasing the light intensity will
increase the rate of photosynthesis at a proportional rate where LI is
inversely proportional to 1/d2 when LI= light intensity and d=
distance (from light source to plant). This is true to a certain point
until another factor is limiting the rate of photosynthesis.
Hypothesis: When chlorophyll absorbs light energy, the light energy
cannot be immediately used for energy conversion. Instead the light
energy is transferred to a special protein environment where energy
conversion occurs. This happens by using the energy of a photon to
transfer electrons from a chlorophyll pigment to the next. When enough
light energy has been harnessed at a reaction center, ATP can be
synthesized from ADP. During this reaction, oxygen is produced as a
by-product and it is the oxygen bubbles that are being measured in the
experiment. The greater the light intensity, the more light energy
that can be transferred and harnessed to fuel reaction in
Light intensity is inversely proportional to the distance squared
because the light energy spreads out as it travels further and further
from its source. Light energy travels along the circumference of an
expanding circle. When light energy is released from a point, the
energy is dispersed equally along the circumference. But since the
circle is expanding, the circumference increases and the same light
energy is distributed along a greater surface.
1. Set up the apparatus as shown in the diagram above but leaving out
the pond weed, funnel, test tube, water, and the sodium hydrogen
2. Fill the beaker with 450 cm3 of water and 50 cm3 of NaHCO3.
3. Select 1 or 2 pieces of pond weed each roughly 5-10 cm long and cut
off the stems.
4. Place the pond weed in the beaker and secure the funnel upside down
over (on top of) the pond weed using the plasticine.
5. Place a water-filled test tube upside down and over the funnel (see
6. Place the ruler so that the "0" measurement is aligned with the
side of the beaker. (distance measured from side of beaker to edge of
7.) Place the lamp directly in front of the plant so that it is 0 cm
away from the beaker. 8.) With the light shining on the plant, record
the number of bubbles emitted in a 1 minute duration. Switch off the
lamp and wait for another minute before taking another reading.
9.) Take 3 readings at the current distance and move the lamp 5 cm
further away from the plant.
10.) Repeat steps 8 and 9 until 3 readings from at least 5 intervals
of 5 cm have been taken.
11.) Proceed to the data analysis stage.
Distance (cm) Light Intensity (LUX) Bubbles per Minute Average
1 2 3
0 (off scale) 240 249 251 246.7
5 11,000 201 222 214 212.3
10 5,800 183 185 188 185.3
15 3,570 154 152 158 154.7
20 2,320 128 118 124 123.3
25 1,780 93 88 90 90.3
30 1,320 67 65 70 67.3
35 1,050 53 50 48 50.3
40 850 38 38 37 37.7
45 690 26 25 24 25
50 580 17 17 18 17.3
The temperature of the water stayed a constant at about 29.5O C
throughout the experiment.
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
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.
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
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
pondweed with carbon dioxide. Performing the experiment with different
volumes of NaHCO3 could vary the amount of CO2. 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. Using translucent color filters in
front the lamps could vary this. 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 is a very important process in nature. It is the
production of energy in the form of glucose involving water from the
soil, carbon dioxide from the air and light energy. It takes place in
all green plants, which use the green chlorophyll, held in
chloroplasts in the leaves, to trap light. The main site of
photosynthesis is the palisade mesophyll cells in the leaf of a plant.
It is these cells that contain the green chloroplasts and are very
well adapted to their task. They are near the upper side of the leaf
where they can obtain the maximum amount of light, they are packed
very closely together and as already mentioned contain green
chloroplasts clustered towards the upper side too.
Plants photosynthesise to produce food chemicals that are needed to
allow them to grow. The main reaction is to produce oxygen and glucose
to be changed into energy during respiration. Glucose is stored in the
form of starch which is insoluble and does not affect the osmosis
taking pace in the plant. As plants respire both day and night this
starch is often used up during the night when photosynthesis cannot
take place. The uses of glucose within the plant are for active
transpiration, cell division, the production of protein and the
production of cellulose. However many other things can also be
produced with the addition of special mineral salts.
In photosynthesis the raw materials are carbon dioxide and water. They
react to form the products of the reaction-oxygen and starch (glucose
that has been stored). The reactions need energy and this comes from
light. The green chloroplasts allow light to be used as energy and
therefore both of these things are like helpers in the reaction.
Glucose is formed firstly then turned into starch to be stored up for
when it is needed.
Although photosynthesis is a complicated process it can be summed up
in this equation:
6CO2 + 6H2O C6H12O6 + 6C2
carbon dioxide water glucose oxygen
It is important to the reaction that certain factors are present when
it is occurring. We know that these are carbon dioxide, water, light
and chlorophyll. Without these the reaction will not take place at
all, but some of them also determine how quickly the reaction takes
place. Water, carbon dioxide and light, along with temperature, all
have a particular effect on the rate of photosynthesis. In terms of
carbon dioxide the levels in the atmosphere do not really alter very
much, but if gardeners wish to increase the rate of photosynthesis
then sometimes carbon dioxide is pumped into greenhouses. Up to a
certain point as temperature goes up so does the rate of reaction.
After it reaches a certain point though the enzymes involved in the
reaction become denatured and stop working properly. A drop in the
amount of water present may cause photosynthesis to occur at only half
the normal rate. The reason for this is the stomata are being closed.
The final factor which contributes is light. We decided to investigate
how this affects the rate of reaction also.
We need to find out how the of presence light and the intensity of it
contributes to the rate of photosynthesis. To be able to measure the
rate we need some type of visible sign that photosynthesis is actually
taking place. We will use a type of plant that grows in water and
produces bubbles when photosynthesising. By counting these bubbles we
can tell how fast oxygen is being given off and therefore produced
from photosynthesis. We will place the pondweed in a beaker containing
water and also a bit of sodium hydrogen carbonate-NaHCO3-(0.5%). This
is put in as it acts as carbon dioxide. If it wasn't there then
another limiting factor may be the cause of the rate changing instead
of just light.
By placing the beaker next to a lamp we can alter the light intensity.
We will move the lamp further away every time and then count the
number of bubbles that are produced within one minute. The weed will
be given two minutes each time to adjust to the new level of light
intensity. To start with the lamp will be 1cm away from the beaker,
then the following distances:
The diagram will help to explain this more clearly.
The rate of reaction will be in number of bubbles per minute (b.p.m).
VARIABLES AND CONSTANTS
The factor that will be changed is light intensity. This is the only
factor that will be changed. The factors that will be kept constant
are the amount of water the weed is put in, carbon dioxide levels,
lamp that is used and temperature. This means that out of all the
possible factors we have chosen only one to monitor.
I predict that as the light intensity is increased the rate of
photosynthesis will also increase. However at a certain point the
light will reach a certain point where the rate will not increase any
more. The chloroplasts will no longer be able to absorb any light so
the rate will stay at its optimum level or even decrease. At this
point light is no longer limiting.
The graph of results will probably look something like this:
Light is limiting at this point Maximum rate of photosynthesis
light is no longer limiting.
1 145 240 189 145 240 189 148 146 222
2 130 210 127 130 210 127 125 130 183
4 97 150 114 97 150 106 118 106 816
8 55 60 40 14 60 45 76 94 600
16 8 5 1 8 5 4 40 48 30
The last set of results is very anomalous and we won't be using it for
And here are the averages of these results.
DISTANCE-CM NUMBER OF BUBBLES PER MINUTE
This is a graph of the averages. The light intensity for the distances
used will be shown in the following units:
1cm- 1000 units
2cm- 250 units
4cm- 62.5 units
8cm- 15.6 units
16cm- 3.9 units
As you can see our results have turned out quite similarly to how we
expected. In the first table of results there are some slightly
different results according to the different experiments that were
done. This shows that it can't have been 100% reliable. It does prove
however that as light intensity is increased the rate of
photosynthesis is increased also. This is because the more light there
is available the more light the chloroplasts can absorb. They use this
light in the reaction as energy; therefore the more energy there is
available the faster the reaction can take place.
On the graph there wasn't a point where the rate started to level off.
We assumed that this would happen, as the chloroplasts would not be
able to absorb any more light energy. However this did not happen so
it may be that we did not take the pondweed close enough to the light
so it would reach a point where the rate could no longer increase.
There was one set of results in the first table that I decided to
leave out. These results were very unusual and anomalous so to include
them would have greatly affected the average. I felt it was best to
leave them out so they would not give us results that were inaccurate.
These anomalous results, among others, can be explained by many
things. First off all our experiment was not completely fair. We did
not attempt to regulate the temperature as well as we could have done
which as we know is a limiting factor of photosynthesis. We could have
put the test tube into a beaker filled with water of a certain
temperature. This would have helped to regulate the temperature so we
would have been certain that light was the only limiting factor. Also
the size of the pieces of pondweed were not all the same so some
people may have achieved different results depending on the size of
their pondweed and therefore how much surface area was available for
photosynthesis to take place in the palisade mesophyll cells. The
distance may not have been completely accurately measured and we could
also have taken each set of results twice to make doubly sure we were
getting an accurate picture.
I think that another way we could have gone about doing this
experiment would have been to use a method where the amount of carbon
dioxide being produced displaces some water held in a burette. The
experiment could be set up as shown:
This would help to give us a greater idea of how much carbon dioxide
is being produced and therefore how fast photosynthesis is occuring.
As the burette fills with the gas water is displaced and the level
drops. By measuring the level every 10 second we would easily be able
to work out the rate of the reaction in the pondweed.
I think that overall our evidence is very reliable and that our
results show what we thought they would. It could have been more
accurate than it is but I think we achieved what we set out to do
which was prove that as light intensity is increased photosynthesis
Investigation into the factors that affect the rate of photosynthesis
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
Glucose can provide energy or carbon, which can manufacture other
molecules in the plant. Which can make new living matter and this is
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
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.
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
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
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
· Increase/Decrease in bubbles
· Temperature Increase/Decrease
· Change in Elodea
· Size of bubbles
· 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.
No. of bubbles
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.
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.