Temperature can change the rate of the reaction as it affects the kinetic energy. As the temperature is increased the atoms of the reactants in photosynthesis gain kinetic energy and so collide more, producing more chance for atoms to join and react together and therefore decrease the time. However, in photosynthesis, chlorophyll has an optimum temperature between 40 and 45ºC and above that it will denature and photosynthesis will not be able occur. Also below a certain temperature chlorophyll will work but as a very slow pace due to the lack of kinetic energy and possibilities to react.
The amount of chlorophyll in a leaf of a plan will be different for each plant. This is due to the amount of space available for chloroplasts in a leaf. The more chloroplasts there are in a leaf the more chlorophyll there will be therefore increasing the rate of photosynthesis as it will be able to absorb more sunlight.
The wavelength of light can change the rate of photosynthesis as different plants absorb different wavelengths of light. Chlorophyll absorbs the light and there are different kinds of chlorophyll that absorb different wavelengths of light. Plants do not absorb green light so if that was the only light available it would be reflected by the plants and so plants would not be absorbing any light. With only green light photosynthesis would not be able to occur as the chlorophyll in the plant would be unable to absorb the light to trigger off the electron in the light stage of photosynthesis.
The rate of photosynthesis is affected by light intensity. This is because if there is a higher light intensity of light reaching a plant then chlorophyll will be able to absorb more light. This means that if more light is being absorbed, more water is being split therefore increasing the amount of hydrogen to be made into NADPH and starting the dark stage of photosynthesis to produce simple sugars. A lower light intensity will decrease the amount of light available for chlorophyll to absorb and so decrease the rate of photosynthesis.
For this experiment I have decided to use light intensity my main factor. This is because it is an easy factor to change with reliable results and a wide possible range. Also, the production of bubbles will be proof of photosynthesis as light directly affects the light stage of photosynthesis. As the light is absorbed by the chlorophyll an electron will be energised and split water. The oxygen will be released form the chloroplast and out of the leaf through the stomata. To see the effect of light intensity on a plant I will change the light intensity that it receives. To do this I will use a light bulb and move it so that the plant it subject to many different light intensities which I will measure using a light intensity meter. I will then be able to count the number of bubbles of oxygen produced and work out that the volume. To be able to so this I will have to use and aquatic plant as I will see the bubbles in the water as they are produced.
As I am using light intensity as my main factor I must keep other factors the same to ensure my experiment is fair and reliable. To do this I will use a 3 percent concentration of sodium hydrogen carbonate in water to ensure that there is enough carbon dioxide available for the plant to use for photosynthesis so that it does not become a limiting factor. I will also use the same piece of elodea in my experiment so that it will have the same amount of chlorophyll and therefore be able to absorb the same amount of light. To control the temperature, the elodea will be immersed in water inside a jar which will be able to block the heat energy from the light bulb entering the jar. To ensure the wavelength of light reaching the elodea can be absorbed I will use a white light bulb which will contain all wavelengths of light and use the same bulb for all of the experiment.
To measure the rate of photosynthesis using light intensity as the main factor I will use an aquatic plant so that I am able to measure the volume of oxygen released by the plant. The oxygen will be produced in the light stage of photosynthesis when an energised electron splits water, allowing the oxygen to be released from the plant. Also, by using an aquatic plant I can control the amount of carbon dioxide and water the plant has available, which will enable me to make sure that there will be no limiting factors affecting the experiment. To measure the volume of oxygen produced I will use a microburette. A microburette is a piece of equipment that allows me to find the exact volume of oxygen produced by a plant. This piece of equipment must be used with an aquatic plant so it is possible to see the bubble of gas. At the start of the experiment the microburette will be placed in water and then using the syringe, the water will be drawn up to fill the microburette. The bulb at the bottom of the microburette holds the tip of the plant which, freshly cut, will produce oxygen. This can then be drawn up the tubing by releasing the screw-clip at the top and pulling the syringe up. As the bubble is drawn up it is possible to use the graduations to measure the volume of gas produced by the tip of the plant. Here is a picture of the microburette:
For this experiment I am going to use the following apparatus:
- Microburette
- 3% concentration sodium hydrogen carbonate
- Aquatic plant - elodea
- Water
- Light bulb
- Stand + clamp
- Meter ruler
- Scales
- 1 large jar
- 1 beaker
- Light intensity meter
- Scales
- Jug
- Scissors
- Stirring rod
- Stopwatch
I will use the microburette so that my experiment will be accurate when measuring the volume of the oxygen produced. To ensure that carbon dioxide does not become a limiting factor in my experiment I will use a 3% concentration of sodium hydrogen carbonate to water. I am going to use an aquatic plant so that I can see the oxygen being produced as bubbles being released from the tip. As I am using an aquatic plant I will need to place it in water to be able to photosynthesise. To change the light intensities I am going to use a light bulb so that I can move it away from the plant. To keep the microburette in the same position throughout the experiment I will use a stand + clamp. I will need a ruler in this experiment to measure the exact distances for the light bulb to be from the jar which will hold the elodea, the water and sodium hydrogen carbonate inside and keep the experiment as at steady temperature. To measure the amount of sodium hydrogen carbonate I need I will first use a measuring jug to measure the water and then find 3% of that and, using scales and a small beaker, I will measure 3% to be exact. For the experiment I am going to use a light intensity meter to measure the intensity of light reaching the elodea. To make sure that the elodea will photosynthesise I will cut the tip fresh using a pair of scissors. For the experiment to be precise and reliable I am going to use a stop watch to keep the time that I leave the elodea to photosynthesise at different light intensities.
For this experiment I predict that a bigger light intensity will increase photosynthesis as there is more light available for the chlorophyll to absorb to use for photosynthesis. This means that in my experiment if the light bulb is closer to the elodea then the volume of oxygen released should be larger than if the bulb was further away. This is due to there being more light available which the chlorophyll can absorb and an electron will become energised and split water into hydrogen and oxygen. This will happen more often if there is more light available because more chlorophyll will be used and therefore more electrons will be energised and be able to split more water. Also, an increase in light intensity would mean an increase in energy which would increase the rate of photosynthesis as a bigger light intensity would increase collisions between the reactants therefore decreasing the time for the products to be made. From my preliminary experiment I also found that after a certain light intensity the rate of photosynthesis will not change as a result of other factors limiting the rate at which light intensity can be the single factor affecting the rate. In my preliminary experiment I used elodea in a 3 percent solution of sodium hydrogen carbonate. I put a thermometer in the solution and then using a ruler I measured how far the bulb was to be and them timed for one minute and counted the number of bubbles produced. I used six different distances to get a good range of results which helped me to decide what distances I would use in my main experiment. In the preliminary I did not use a light intensity meter as I did not feel it necessary to because I was gathering information to use in my main experiment. The results from my preliminary are:
.My preliminary experiment, although was not very accurate and did not have any lux readings, was able to show me that after 50cm the light intensity will not change the rate pf photosynthesis. In the preliminary experiment I did not use a microburette but only counted the bubbles as they were produced. This I found to be a very inaccurate way to measure the volume produced as the sizes of the bubbles produced differed. By using the microburette in my experiment I will be able to get precise and reliable results compared to that of my preliminary.
At the start of this experiment I am going to first get a jar and fill it with 700ml of water. Then I will measure 21g of sodium hydrogen carbonate and using a stirring rod dissolve the sodium hydrogen carbonate into the water. Once I have placed the jar on a table I will place the end of a meter ruler next to the end of the jar. This will ensure that as I place the light bulb next to the meter ruler it will be the exact measurement away from the jar and elodea. Then I am going to get a stand and clamp and attach the microburette to it. I will then cut a piece of elodea fresh and place it in the water and the fresh tip in the bulb of the microburette. Once the equipment is set up I will turn the light on at 10cm, start the stopwatch, and allow 1 minute for the elodea to adjust to the light. When doing this the clip of the microburette will be unscrewed to allow any bubbles produced to be released straight into the tubing. After 1 minute I will draw any bubbles up and then close the screw-clip. When closed I will start the stopwatch. I am going to time for 2 minutes to allow the elodea to produce oxygen. When 2 minutes is over I will open the screw-clip and slowly pull the syringe to draw up the oxygen and measure the volume produced using the graduations of the tubing. I will repeat the method for each measurement of which I will get 3 readings. Due to my preliminary experiment I have chosen to use the measurements of 10, 20, 30, 40, 50 and 60cm. This is because in my preliminary after 50cm the amount of bubbles produced stayed the same. However, due to the lack of reliability from my preliminary I decided to check this and measure up to 60cm. Also, in my preliminary I did not use a microburette, only counted the bubbles which is not an accurate measurement of the volume of oxygen produced. Using the microburette will give a more precise measurement and the actual volume of oxygen produced. Also, in my preliminary experiment I only timed for 1 minute to count the bubbles but using the microburette I think it will be better to leave it for 2 minutes to get a larger volume of oxygen being produced. This should help when the light bulb is at a further distance so the plant has more time to photosynthesise.
Here are the results from the experiment:
As you can see from the results I have my experiment was accurate and I got a good range of reliable results. They showed me that as light intensity increases so does the rate of photosynthesis. This is due to there being more light available for chlorophyll to absorb and use for photosynthesis and therefore produce more oxygen. It also means that my prediction was also correct in that a bigger light intensity would increase the amount of chemical energy being used to split more water. However, my results show that the rate at which plants photosynthesise is not constant as the difference between the different lux readings changes as does the difference between the volumes. This means that light intensity does not change at a constant rate and so must mean that other factors are still affecting the rate of photosynthesis so light intensity cannot affect photosynthesis at a constant rate.
I feel that my experiment was very accurate as I used a microburette to get a good set of results. However, one inaccuracy I had was that I was not sure of the temperature inside the beaker. This means that if the temperature increased during the experiment it may have jeopardized the results and made them inaccurate.
To make the experiment more accurate I would have used a thermometer in the jar to check the temperature. This would have ensured that the temperature stayed the same as if it increased then I would have been able to add water to reduce the temperature. Also, to make the experiment more accurate I would have liked to keep the time more precise. This is because at times it was hard to open the screw clip at the same time on every result and so some bubbles may have formed. However, as my results are very similar I do not believe that this caused a problem. In the experiment I found no anomalous results which suggest accurate and reliable results. All of the results for each lux reading were the same except for the first readings but they evened out when I averaged them.
I feel that my experiment was very accurate and as a result there is very little I could do to carry out my experiment in a better way. If it had been possible it may have been better to complete the experiment in darkness. This would have meant that the only light reaching the elodea would have been from the light bulb. This is likely to have improved the reliability of the experiment as no extra light could have changed the rate of photosynthesis. However, as the other light was constant it should not have made any effect on my results.
The results I received from my experiment are very good and show the reliability of my experiment. I do not know of any way to improve the reliability of my experiment as I had no anomalous results. Also, my results from each experiment were the same except for at 10cm which means that another set of results would not be needed.
From this experiment I believe that I have found enough evidence to support a firm conclusion. The experiment shows that as light intensity increases the rate of photosynthesis also increases. Therefore, the light stage of photosynthesis is a quick reaction, quickly splitting water to produce hydrogen and oxygen. My experiment also proves that the oxygen produced is a by product and so released from the plant.
To extend my investigation on the rate of photosynthesis I think it may be useful to experiment other factors to see how they affect the rate of photosynthesis. This would ensure that all factors affect photosynthesis in a similar way to light intensity.
