Chlorophyll-Different species of plant have different rates of Photosynthesis. This is because of the different leaf structures of the plants. Even plants of the same type may have a slight difference in the rates of photosynthesis. This is because one plant may have slightly more or less chlorophyll in the leaves to absorb the light energy than the other. The size of the plant is also important. This is because it would affect the amount of surface area for gas exchange. The only solution for controlling this variable is by using the same plant throughout the experiment.
The role of light energy in photosynthesis is to break up the bonds in the carbon dioxide and water molecules and to make new bonds to produce glucose and oxygen molecules.
The role of chlorophyll in photosynthesis is to absorb the light energy which is used to break up the bonds in the carbon dioxide and water molecules and to make new bonds to produce glucose and oxygen molecules.
LIMITING FACTORS
Light, carbon dioxide, water, temperature and chlorophyll are all limiting factors. This means that even if there is more than enough of every other variable, the rate of photosynthesis will still be limited by the limiting factor until there is a sufficient amount of the limiting factor to increase the rate of photosynthesis further. Until then, the rate of photosynthesis cannot increase.
SIMPLE PREDICTION
I predict that as the light intensity is increased, the rate of photosynthesis will also increase. This is because the plant will receive more light. Thus, the plant will be able to break up more bonds in the carbon dioxide and water molecules and create more new bonds to produce glucose and oxygen molecules. However, when one of the factors becomes limited, the rate of photosynthesis will stop to increase.
COMPLEX PREDICTION
I predict that the limited factor that will be involved is chlorophyll. This is because:
- Light will not be a limiting factor as I will be increasing the light intensity throughout the experiment by moving the source of light closer to the plant.
- Water will not be a limiting factor as the beaker containing the plant will contain more than a sufficient amount of water.
- Carbon dioxide will not be a limiting factor as I will be adding sodium bicarbonate into the water which will contain a sufficient amount of carbon dioxide.
- Temperature will not be a limiting factor as I will be doing the experiment in the summer when the temperature is suitable for the chlorophyll enzymes to work.
- I will not be able to add or remove chlorophyll from the leaf of the plant. This is why chlorophyll will not be the limiting factor.
The following graph is what I predict that my graph will look like for the rate of photosynthesis as the source of light is brought closer to the plant:
The line evens out because
Of the limiting factor
Bubbles per minute The rate of photosynthesis
(Rate of Starts to decrease as the
Photosynthesis) Lamp is moved away from
The plant
10 Distance of lamp from plant
As you can see, the rate of photosynthesis does not start to decrease immediately. This is because the limiting factor is preventing the plant to break up and produce bonds to the best of its ability because the plant always has the same amount of chlorophyll to absorb the light energy. As the lamp is moved away from the plant, the light intensity decreases. This means that the plant will not be able to break up the bonds of carbon dioxide and water and produce new bonds for the glucose and oxygen at the same rate. This is why the amount of bubbles decreases.
METHOD
The apparatus required for this experiment is:
- Pondweed
- Beaker
- Funnel
- Test Tube
- Plasticene
- Sodium Bicarbonate
-
Ruler
- Lamp
- Stop Watch
Test tube
Sodium Bicarbonate
Beaker
Water Lamp
Funnel
0 cm 100
Plasticene Pondweed Ruler
Instructions:
- Set up the apparatus as shown in the diagram above.
- Place the lamp directly in front of the plant so it is 10 cm away from the beaker and then turn it on.
- Wait one minute for the plant to adjust to the level of light timing yourself using the stop watch.
- Immediately after the minute is over, time yourself for another minute, during which you have to count the amount of bubbles emitting from the plant.
- After the minute is over, switch the lamp off and record your results.
- Repeat the experiment with the lamp at the same length, twice, recording your results each time.
- After this, repeat the whole experiment moving the lamp 10 centimetres away each time until you have completed the experiment for when the lamp is 100 centimetres away from the plant.
- Put all your results into a table working the averages of the results at different lengths.
- Finally, record your results in a graph.
FAIRNESS
I made this experiment fair by:
- By changing only the light intensity in the whole experiment and keeping all the other variables the same. This would help to prevent any anomalous results in the experiment.
- Using the same pondweed for every experiment. This makes the experiment fair because by changing the pondweed throughout the experiment, you would change the surface area of the leaves, amount of chlorophyll, etc.
- Trying to keep the temperature of the room the same throughout the experiment. This makes the experiment fair because by increasing the temperature, you can make the chlorophyll enzymes react faster and by reducing the temperature, you can make the chlorophyll enzymes react slower.
- Keeping the same amount of sodium carbonate in the baker of water. This makes the experiment fair because by adding more sodium bicarbonate, you will also be making more carbon dioxide available for the plant to use. Thus, increasing the rate of photosynthesis.
- By using the same amount of water during the experiment. This makes the experiment fair because adding water would speed up the rate of photosynthesis and reducing water would slow down the rate of photosynthesis.
- By doing the experiment for only one minute each time. This makes the experiment fair because the plant will not have more or less time during the whole experiment to produce the bubbles.
SAFETY
To make this experiment safe, I carried it out on a dry surface. This would prevent any electrical accidents while using the lamp.
RELIABILITY
I made this experiment reliable by:
- By repeating the experiment three times at each length. This would help to prevent any anomalous results.
- Checking the apparatus to check that they were all functioning properly. This would help to make the experiment reliable because faulty equipment would encourage unreliable results.
RESULTS
RESULTS TABLE
ANALYSIS
My results show that as I moved the lamp away from the plant, the number of bubbles per minute decreases. This means that as the lamp is moved away from the plant, less of oxygen, one of the products of photosynthesis, is being produced. This is because the light energy is decreasing which means that the plant slows down the process of breaking up and producing new bonds.
I predicted that as the light intensity is increased, the rate of photosynthesis will also increase. Looking at my graph, I can see that my prediction was correct because as the lamp moves away from the plant, the rate of photosynthesis decreases which means that if I were to move the lamp closer to the plant instead, the rate of photosynthesis would increase.
I also predicted that there would be a limiting factor and that the limiting factor would be chlorophyll, but, looking at the results, this is not true. I can see this because the line on the graph does not even out as it does in my predicted graph.
EVALUATION
Overall, I would say that the experiment was successful because my simple prediction was supported by my results. However, I cannot say that the experiment was perfect for several reasons:
- I could not keep the temperature of the room exactly the same throughout the whole experiment. This means that the temperature of the plant will have changed slightly during the process of the experiment. Also, the lamp will also have created some heat during the experiment which would also alter the temperature. An improvement I could make to this experiment would be to use a heat sink, which will keep heat out but let light through. This would prevent the plant from rising in temperature.
- All three attempts of the experiment were never the same which means that they were not totally reliable. However, the results are fairly close to the line of best fit on the graph so I can say that my results were reasonably reliable.
- Some of the bubbles that were emitted from the plant were bigger than others which means that there was a slightly different amount of oxygen in each of the bubbles. This means that the results were not very reliable. Another improvement I could make would be to use a gas syringe instead of counting the bubbles emitting from the plant. This is a more accurate way of measuring the amount of gas being produced by the plant.
To improve the accuracy of the results, instead of moving the lamp 10 cm away from the plant each time, I can move the lamp 5 cm away from the plant. Also, instead of doing the experiment until 100 cm, I could do the experiment until 200 cm.
To extend this experiment, I could explore other factors that affect the rate of photosynthesis. For example, instead of using light intensity as the variable, I could use the amount of carbon dioxide as the variable. Also, I can explore how different coloured lights affect the way in which plants photosynthesize. To do this, I could place white, red, green and blue coloured filters in front of the lamp and do the experiment with a different coloured filter each time.
