Top-Rated Free Essay
Preview

How does light intensity affect the rate of photosynthesis?

Good Essays
2746 Words
Grammar
Grammar
Plagiarism
Plagiarism
Writing
Writing
Score
Score
How does light intensity affect the rate of photosynthesis?
How does light intensity affect the rate of photosynthesis?

Poorly Pondweed

Questions

1) How does light intensity affect the rate of photosynthesis?

2) How does temperature affect the rate of photosynthesis?

sunlight

carbon dioxide + water glucose + oxygen

chlorophyll

sunlight

6CO2 + 6H2O àààààà C6H12O6 + 602

chlorophyll

Prediction

I predict that the more intense the light, the higher the rate of photosynthesis. To photosynthesise, plants need light. It provides the energy for the process to happen. Chlorophyll is an enzyme and it speeds up the reaction. If a plant does not get enough of either of these things, photosynthesis will not happen as quickly, if at all. Therefore, I predict that when the light is not very intense we will not see so many bubbles being produced. This is because the plant will not have so much energy (derived from light) to activate photosynthesis. All reactions require a certain activation energy, and if this is not reached the reaction will occur more slowly.

I think that as we move the lamp away (and therefore reduce the light intensity) from the elodea pondweed the number of bubbles produced will decrease steadily. For instance, say at 10cm distance 50 bubbles are counted, it is likely that at 20cm distance 25 bubbles will be counted, as the lamp is twice the distance away. This means the rate of photosynthesis is halved. I think that if we move the lamp any further away than 50cm no bubbles at all will be produced because there will simply not be enough light for photosynthesis to work.

I predict that for temperature, it will not be a case of an increase in x = an increase in y. I predict that there will be a peak where photosynthesis happens the quickest at around 40-50°C. Chlorophyll is an enzyme, therefore it requires some heat to work, but if it is overheated it stops working. Enzymes work rather like a lock and key. It is important that they are a very specific shape for their purpose (in this case chlorophyll joins carbon dioxide and water together to form glucose). If a key is heated too much, it melts and becomes denatured. It will no longer fit the lock it was designed for. This is why enzymes start to work less well at high temperatures.

I think that at the lower temperatures (i.e. 0-20°C) we will not see many bubbles being produced. This is because enzymes need energy to work, which they get form heat (as well as light). So when the temperature is quite low the chlorophyll does not have much energy, therefore the rate of photosynthesis will be low. As the temperature increases, I predict that the rate of photosynthesis will increase (more bubbles will be produced). This is because more heat energy is being provided to the chlorophyll, meaning that photosynthesis can happen more quickly. However, I think that when the temperature reaches 50°C and above, the rate of photosynthesis will decrease, because the chlorophyll will become denatured, and unable to activate photosynthesis as well. Eventually I predict that no bubbles at all will be produced, say around 100°C. So we should see a pattern where the rate increases dramatically between 0-50°C, but then it should decrease dramatically from 50-100°C.

Plan

Apparatus

*

desk lamp

*

Elodea pondweed x 2

*

boiling tube x 2

*

paperclip x 2

*

250ml glass beaker x 2

*

test tube rack

*

thermometer

*

sodium hydrogen carbonate solution

*

stopwatch

*

ice

*

tongs

*

metre stick

*

black A4 paper

*

sellotape

*

scissors

*

1ml pipette

Safety

*

Take care of the light bulb, which may get very hot.

*

As you will be using electricity (for the light bulb) and water at the same time, special care must be taken.

*

As a precaution try not to drop any water onto the beaker in the light intensity investigation as it will be hot and may crack.

Method

Preliminary work...

Take two green, healthy pieces of pondweed, with lots of leaves on, and about 8-10cm long (you are taking two so as to find which one photosynthesises the best, and therefore produces the most amount of bubbles). Cut the ends of them diagonally, and strip part of the stem of leaves. This is simply so we can see the bubbles as they come out of the stem. Attach a paperclip to the bottom end of each piece of pondweed (the part with leaves on). This acts as a weight so the pondweed does not float above the surface of the water. Next, put each piece of pondweed in a boiling tube, and fill them with water until the top of the pondweed is well covered, but make sure there is still enough room for some sodium hydrogen carbonate.

Add about 3 pipettes of sodium hydrogen carbonate solution to each boiling tube. This is to provide carbon dioxide to the plant as it is vital in photosynthesis. With scissors, cut the end of each piece of pondweed diagonally while it is still under the water. It is important that you do this while submerged in water because you are removing any air locks in the xylem tubes of the plant, which would prevent oxygen bubbles from escaping. This would lead to anomalous results.

Half-fill a glass beaker with water, and leave the boiling tubes containing the pondweed there for approximately one minute. Check them to see which is producing bubbles the most rapidly. This is the one you will use for both the experiments.

You must do the light intensity investigation first, because we do not want the pondweed to be damaged after being in high temperatures. This is also why you will do the lower temperatures first in the temperature investigation.

For the light intensity investigation...

Set up the apparatus as shown in the diagram on the following page.

Make sure the black paper is attached to the beaker so that only the front of it is exposed to the light. This is to ensure that the plant takes in only the light from its own lamp. This is why you must also make sure all the main lights in the room are turned off.

Put the water bath with the boiling tube with the best piece of pondweed in on the test tube rack. This is just so it is as close to the level of the light as possible. Put the lamp 10cm away from the water bath. Allow 2 minutes adjustment time for the pondweed so it can get used to its new environment. Otherwise the plant will not produce oxygen at a steady rate. Then, start the stopwatch, and begin counting bubbles. After one minute, stop the stopwatch and note down how many bubbles were counted. Repeat this paragraph 3 times.

Place the lamp 20cm away from the water bath. Leave the pondweed for 2 minutes, as adjustment time for it to get used to its new environment. Otherwise the plant will not produce oxygen at a steady rate. Then, start the stopwatch and begin counting bubbles. After one minute, stop the stopwatch and note down how many bubbles were counted. Repeat this paragraph three times.

Repeat the previous paragraph except for 30, 40 and 50 cm away from the water bath. This should give reliable results, because of repeated readings and the range of 10-50cm in intervals of 10cm.

If the pondweed stops bubbling at any time during the experiment, this may be due to an air lock in the xylem tubes of the plant. In this case you need to cut the end of the pondweed with no leaves on while it is still under the water. This should stop the air from blocking up the xylem tubes of the plant. The other problem may be that the plant has used up all the carbon dioxide form the sodium hydrogen carbonate solution. In this case you need to add two or three 1ml pipettes of the solution to the water the pondweed is in.

For the temperature investigation...

Set up the apparatus as shown in the diagram below.

Ensure that the black paper is attached to the water bath so that only a small area at the front of the beaker is exposed to the light. Using the previous investigation, find the distance in which the pondweed produced the greatest amount of bubbles. This is the distance you will use throughout the whole temperature investigation, because then we will have more reliable results. There is no need to move the lamp at any time during the experiment.

Put some ice in the water bath, along with the thermometer. When the temperature has reached between 0-10°C, leave the pondweed for 2 minutes to adjust to its new environment. Otherwise, the plant will not produce bubbles at a steady rate. Then, start the stopwatch and count the bubbles produced. After one minute, stop the stopwatch and note down how many bubbles were counted (it does not matter if no bubbles were produced, just write down 0). Repeat this paragraph 3 times.

Take some of the ice out of the water bath, but do not remove the thermometer. When the temperature is between 11-20°C, leave the pondweed for 2 minutes to adjust to its new environment. Then, start the stopwatch and start counting the oxygen bubbles. After one minute note down how many bubbles have been produced. Repeat this paragraph 3 times.

Repeat the previous paragraph for 21-30°C, 31-40°C and 41-50°C, adding ice or warm water from the tap as necessary. If the temperature goes above or below the temperature needed, then add ice or warm water accordingly.

If the pondweed stops bubbling at any time during the experiment, it may be due to an air lock in the xylem tubes of the plant. In this case you need to cut the end of the pondweed with no leaves on while it is still under the water. This should stop the air from blocking up the xylem tubes of the plant. The other problem may be that the plant has used up all the carbon dioxide form the sodium hydrogen carbonate solution. In this case you need to add two or three 1ml pipettes of the solution to the water the pondweed is in.

Variables from studentcentral.co.uk

For the light intensity investigation...

*

the dependant variable is light intensity

*

the independent variable is the rate of photosynthesis

*

the controlled variables are 1) the power of the light bulb

2) the piece of pondweed

3) adjustment time

4) temperature

*

the range is 10-100cm in intervals of 10cm

*

number of readings - 3 for reliability

For the temperature investigation...

*

the dependant variable is temperature

*

the independent variable is the rate of photosynthesis

*

the controlled variables are 1) the power of the light bulb

2) the piece of pondweed

3) adjustment time

4) the distance the lamp is from the water bath

*

the range is 0-50°C in intervals of 10°C

*

number of readings - 3 for accuracy

Results

For the light intensity investigation...

Distance from lamp (m)Number of oxygen bubbles produced in 1 minute

123Average

0.125262525

0.222191920

0.311131312

0.49778

0.54333

For the temperature investigation...

Temp. range (°C)Actual temp. (°C)Number of oxygen bubbles produced in 1 minute

123Average

0-1040000

11-20151011

21-30248968

31-403610131111

41-504515141515

Graphs

Conclusion

I conclude that the greater the light intensity, the quicker the rate of reaction. For photosynthesis, plants require light and chlorophyll to make the reaction happen. They are not constituents of glucose but are still vital. So, when the lamp was further away from the pondweed the plant was unable to photosynthesis as well as when the lamp was right up close to the pondweed. When the lamp was 50cm away, an average of just 3 bubbles was produced, compared to an average of 25 for 10cm away. As the lamp was moved further away, the light intensity increased, therefore the rate of photosynthesis increased. The pondweed had more light energy for photosynthesis and was therefore able to produce more oxygen bubbles in one minute.

Looking at the light intensity graph, you can see a trend. It shows that the rate of photosynthesis and light intensity are proportional to each other. This is because there is a straight line of best fit going down as the distance increases (when the distance is increasing this is the equivalent of the light intensity decreasing).

In my prediction I said that for double the distance there would be half the amount of bubbles, but this did not happen between 10cm and 20cm. 10cm away from the lamp the pondweed produced an average of 25 oxygen bubbles. At 20cm the plant produced 20, and this is not even close to half of 25. However, 40cm away from the lamp, an average of 8 bubbles was produced by the pondweed, which is a little under half of the 20 bubbles at 20cm. So there was some truth in that prediction. Perhaps my results were slightly anomalous.

I also conclude that temperature affects the rate of photosynthesis in that there is a peak around 40-50°C. At the lower temperatures the plant was unable to produce many bubbles, if at all. Unfortunately due to time restrictions we were unable to go up to 100°C, but I have made an estimate of what would have happened on the temperature graph. It would have decreased until eventually the pondweed was not producing any bubbles at all.

Chlorophyll is used to make photosynthesis happen in plants. It is an enzyme, and all enzymes need some heat to activate them. This is why at the lower temperatures the rate of photosynthesis was so low. As the temperature increased, so did the rate of photosynthesis. At around 40-50°C was a peak. This was when the rate of photosynthesis was the highest. After that, it decreased. You might expect the trend to be that the higher the temperature, the higher the rate of photosynthesis, but this is not the case. Enzymes work rather like a lock and key. They are specifically designed for one purpose - in the case of chlorophyll it is to activate photosynthesis. If a key is heated up, it will melt and become denatured and can never be restored to its original shape. This is how enzymes work. When the temperature is over 50°C, the enzymes are damaged and no longer fit the "lock" they were designed for. This is what causes the peak.

On the graph you can see this trend of a peak (although the second half of the graph is an estimate). It is a lot clearer than looking at the results table. It supports my prediction, unlike for the light intensity investigation, although they do not support what I said about the peak, as I have only been able to estimate.

Evaluation

I think that the procedure used was quite suitable, as we managed to achieve fairly reliable results. However, when dealing with living things the results can never be that accurate, because living things do not work at a constant rate. So we cannot know if the plant was working at a high or a low rate or somewhere in between when we did the experiment. I think it might have been working at a low rate judging by the fact that the most bubbles produced in the whole experiment was 25. This is nowhere near as high as I expected. However, at least the results were not completely anomalous and I was able to draw reasonable conclusions from them.

There is not really any way in which we could improve this procedure, because living things are so unreliable. However, we could take results over a period of several weeks for more accuracy. This way we would catch the pondweed at times when it was working at a high level and at times when it was working at a low level.

Another thing that was not very suitable was the way of measuring the rate of reaction. Counting the bubbles got very boring and I could easily have miscounted, leading to anomalous results. A better way would be to find some way of collecting the oxygen bubbles in a capillary tube and measuring how far along the oxygen goes. We would have to fill the capillary tube with water and seal the top, and attach the tube to the pondweed. Although fiddly this would be more reliable.

There were no anomalous results, but if there were there are many reasons why it could be. For a start, I could have miscounted the bubbles. Also, the pondweed might not have been bubbling properly due to an air lock that I did not notice. Similarly, there might not have been enough sodium hydrogen carbonate solution, which provides carbon dioxide for the plant. Also, there is the possibility that the piece of pondweed used was damaged - for example perhaps it had been heated up too much and the chlorophyll had become denatured. Because there were no anomalies, this supports my prediction in that they were reliable.

You May Also Find These Documents Helpful

  • Good Essays

    This lab has been created in order to find what extent does distance from a light source (5cm, 10cm, and 15cm) affect the rate of photosynthesis (measured in bubbles / 3 min) in Elodea water plants. Hypothesis: More amount of time under the light will cause the plant to give out more glucose and O2. Also, if the light is closer, the process will be faster. The procedure for this would be to leave the Elodea plant in water with sodium bicarbonate (baking soda increases carbon dioxide in water), set up the lamp at 5cm distance and start the timer for 3 minutes. Overall results are that after 9 minutes (3 minutes intervals between the light distance), the solution gave off 4 bubbles.…

    • 611 Words
    • 3 Pages
    Good Essays
  • Better Essays

    Research question: How does the concentration of sodium bicarbonate relate to the amount of oxygen produced by Elodea (Canadian pond weed) in the process of photosynthesis?…

    • 1242 Words
    • 7 Pages
    Better Essays
  • Satisfactory Essays

    Case Brief

    • 290 Words
    • 2 Pages

    As light intensity increases then the rate of photosynthesis increases linearly until a point is reached when the rate levels off. The light intensity beyond which the light response curve plateaus is called the light saturation point of photosynthesis. At this point increases in light intensity do not cause increases in photosynthetic rate, so other factors (eg. CO2 levels) apart from the supply of light must be limiting the photosynthetic process.…

    • 290 Words
    • 2 Pages
    Satisfactory Essays
  • Better Essays

    Figure 2. The rate of photosynthesis in elodea plants with different color light filters which include clear, red, blue, and green. The color that produced the highest rate of photosynthesis was clear at .48, then red at .28, and finally green at…

    • 1719 Words
    • 7 Pages
    Better Essays
  • Satisfactory Essays

    Photosynthesis Lab Report

    • 566 Words
    • 3 Pages

    The closer the light is the plant, and the higher the wattage of the light, the faster the rate of Photosynthesis. So, the 150 watt light bulb at 5centimeters will have the highest rate of photosynthesis.…

    • 566 Words
    • 3 Pages
    Satisfactory Essays
  • Better Essays

    So big plants can produce more oxygen that little ones. In my experiment I am going to take pieces of pondweed of different length, I predict that this change will increase the number of oxygen bubbles, because there will be more surface to get more light. For example, Some plants in rainforests are very tall and have giant leaves, so they can get more sunlight. In this experiment I am going to simulate all the necessary conditions for the plant to produce oxygen (and…

    • 1045 Words
    • 5 Pages
    Better Essays
  • Good Essays

    The higher the light potential is the more packets of light are said to be hitting the plant. At low intensity’s of light photosynthesis is know to be low, while at higher light intensity’s the rate of photosynthesis is higher. With this being said As the light intensity is risen from low light intensity to high light intensity, the rate of photosynthesis will increase because there is more light available to drive the reactions of…

    • 2047 Words
    • 9 Pages
    Good Essays
  • Satisfactory Essays

    Photosynthesis Review

    • 470 Words
    • 3 Pages

    A student prepared two beakers with identical sprigs of a water plant as shown below. She placed one beaker in the shade and the other beaker beside a fluorescent lamp. She then systematically changed the distance of the beaker from the lamp. She counted the bubbles given off by each sprig of the water plant. Shown here is the graph of the data for the beaker she placed in the light.…

    • 470 Words
    • 3 Pages
    Satisfactory Essays
  • Good Essays

    Photosynthesis Lab

    • 1665 Words
    • 7 Pages

    Temperature, light, and carbon dioxide are all variables that affect the rate of photosynthesis. Temperature was tested through the experiment. The scientific concept explains that higher temperatures produce a higher rate of photosynthesis. This conclusion was supported by the data found because the higher temperatures had a higher rate of photosynthesis. In most chemical reactions, the reaction rate increases with temperature. If temperature is cold (between 0 and 10 C), the enzymes responsible for photosynthesis move to slowly to meat the substrate and will be too cold for a reaction to occur. In medium temperatures (10 to 20C), the enzymes responsible for photosynthesis are functioning at their optimal level. This means that the rate of photosynthesis is high. At high temperatures (usually above 30C), enzyme function begins to slow down and at 40C, the enzyme denatures and no longer functions. The data from this experiment support the concept. However, the enzyme did not denature at the 45C and 55C temperatures. This could be due to external factors such as the fact that the algae was encapsulated in beads as well as in a solution in a test tube, therefore the algae might never have reached…

    • 1665 Words
    • 7 Pages
    Good Essays
  • Satisfactory Essays

    Different wavelengths of light will effect to rate of photosynthesis. I will test this by exposing the pondweed to different wavelengths of light to see how it reacts.…

    • 400 Words
    • 2 Pages
    Satisfactory Essays
  • Good Essays

    We can see through the results that there isn’t a normal proportional relationship between the wavelength of the light and the rate of photosynthesis and instead it starts relatively high then decreases and increases again. The colour red gives the highest rate of photosynthesis (89 bubbles per minute) with blue giving the second highest rate of photosynthesis (70 bubbles per minute), and yellow giving the third highest rate of photosynthesis (64 bubbles per minute) and green with by far the least (44 bubbles per minute). Although, we can see no direct correlation between the rate of photosynthesis and the wavelength of the light used, we can see a relationship between the colour of the leaf, the rate of photosynthesis and the colour of light used. With colours that are similar to the colour of the leaf such as green and yellow, lower rates of photosynthesis were identified while colours that were opposite to the colour of the leaf gave the highest rate of photosynthesis such as red. All of the results compared to the control showed a lower rate of photosynthesis as white light is made up of a mixture of all wavelengths of light, including wavelengths that cause a very high rate of photosynthesis.…

    • 585 Words
    • 3 Pages
    Good Essays
  • Good Essays

    Photosynthesis Lab Report

    • 894 Words
    • 4 Pages

    Determining the Effect of Light Intensity on Photosynthesis Avalon Pernell, et al Abstract: The purpose of this lab was to determine how light affected photosynthesis, specifically the production of O2 bubbles. It was predicted that when the light was more intense the O2 bubble production will be high. Conversely, when the light was less intense the O2 bubble production will be lower.…

    • 894 Words
    • 4 Pages
    Good Essays
  • Powerful Essays

    Photosynthesis Lab Report

    • 1335 Words
    • 6 Pages

    This process occurs in plants and some algae. Plants need only light energy, CO2, and H2O to make sugar. The process of photosynthesis takes place in the chloroplasts, specifically using chlorophyll, the green pigment involved in photosynthesis.…

    • 1335 Words
    • 6 Pages
    Powerful Essays
  • Good Essays

    Light intensity will have an effect on plant growth. With an increase in light intensity there will be plant growth at a faster rate in comparison to when the light intensity is low where plant growth is limited and will take place slowly. When there’s too much light intensity, the light intensity will no longer become a limiting factor. A limiting factor is a factor that controls any particular process at the minimum rate. This control the rate of the process which in this case is the light intensity. This can also be called the rate limiting factor as it affects the rate of photosynthesis.…

    • 797 Words
    • 4 Pages
    Good Essays
  • Good Essays

    A few requires more, and some can either do photosynthesis in less light source however with temperature and carbon dioxide, daylight is additionally a noteworthy need for each plant in this world. Without sun there can't be any presence of life on Earth. Taking a gander at the theory and perception done of both the investigations, I might want to presume that more dislodging happens, more photosynthesis happens, accordingly expanding the rate of photosynthesis. Test 2 with relentless light given had more relocation when contrasted with the first investigation in which the light source was been switch on and off in some timeframe. Another variable which is the room temperature, will likewise influence the test in light of the fact that with daylight and carbon dioxide, plants have their own particular prerequisite for temperature to develop and do the photosynthesis handle as well thus does the Hydrilla plants…

    • 830 Words
    • 4 Pages
    Good Essays