Light Intensity Analysis draft for BY6 assessment-
Analysis (A)-
(a) Description of trend shown by results:
It is clear from my graph that there is a negative correlation. As the distance between the lamp and cabomba sp increased, the mean distance moved by the NAHCO3 solution in the manometer over 3 minutes decreased. The mean distance moved by NAHCO3 solution in the manometer over 3 minutes falls rapidly by 100 mm between the distances 4 and 12 cm. Yet, the mean distance moved by the NAHCO3 solution in the manometer over 3 minutes falls at a slower rate between the distances 12-20 cm from 31 mm to 2 mm.
(b) Comment made on the consistency of results:
At distances x,y and z cm between the cabomba sp and the lamp, the repeated sets of data have a small range which is representative of the short error bars. This conveys that the means of these data sets are reliable. However, for distances x and y cm between the cabomba sp and the lamp, the related sets of data have a large range which is representative of long error bars. These data sets are less reliable and it must be questioned as to whether the mean obtained from these data sets is truly representative.
(c) Comments on the use or suitability of error bars:
For the distances x and y the data obtained does not overlap. It therefore may be argued that the mean values for these data sets are significantly different. However, some of the results that I obtained for different distances between the lamp and cabomba sp do overlap. The error bars for the distances x, y and z overlap which indicates that the mean distances moved by NAHCO3 solution in the manometer over 3 minutes for these data sets are not truly different. Furthermore, it means i cannot be confident that varying the distance between the lamp and cabomba sp, significantly affects the distance moved by NAHCO3 solution in the manometer over 3 minutes.
(d) Statement commenting on sources of uncertainty/accuracy of measurement,
(e) Two suitable suggestions for improvement:
The first source of uncertainty is the ability to take an accurate measurement. The accuracy of my measurement is limited to the nearest mm by the manometer scale. The ability to take an accurate reading may also be affected by parallax error. This is where the distance moved by the NAHCO3 solution in the manometer over 3 minutes can be distorted as a result of taking a reading at a different angle. Furthermore, the continuous movement of the NAHCO3 solution in the manometer can also affect the accuracy of measurement. Accuracy of measurement can be improved by fixing a camera parallel to the manometer and taking a photograph directly on 3 minutes. This will eliminate the problem of parallax error as well as the issue of the NAHCO3 solution constantly moving.
The second source of uncertainty regards the temperature. It is expected that as the distance between the lamp and cabomba sp decreases the temperature of the test tube containing the cabomba sp will be higher. Therefore the rate of photosynthesis will be greater, as the enzymes involved in the process will have a greater kinetic energy and therefore more successful collisions between enzyme and substrate will occur resulting in more enzyme-substrate complexes being formed. This in turn would affect the reliability of my results. In attempt to reduce the effect that varying temperature has on the distance moved by the NAHCO3 solution in the manometer over 3 minutes a heat barrier could be positioned between the lamp and test tube containing the cabomba sp. Furthermore, an LED bulb could be substituted in which would generate less heat.
(f) Concise explanation of results using relevant and sound biological knowledge or comparison with theoretical expectations if appropriate:
The NAHCO3 solution is displaced in the manometer as a result of oxygen production via the process of photosynthesis (6CO2 + 6H20 C6H12O6 + 6O2). The oxygen is produced from the photolysis of water a process which occurs during the light dependent stage of photosynthesis. The distance between the lamp and cabomba sp is proportional to light intensity with the equation 1/d^2. Therefore as the distance between the lamp and cabomba sp decreases there is an increase in the number of photons of light which are being absorbed by photosystem II. These photons are passed to chlorophyll a in the reaction centre which in turn cause two electrons to be emitted and raised to a higher energy level before being picked up by an electron acceptor. Photosystem II is now unstable and requires electrons which are provided by the process of photolysis. Photolysis involves the splitting of water into electrons, hydrogen ions and oxygen. Oxygen is a waste product of photolysis and therefore as light intensity increases (proportional to distance between the lamp and cabomba sp), photolysis occurs more as electrons are required to replace the ones displaced from photosystem II, meaning more oxygen is produced as a result. The oxygen produced causes the NAHCO3 solution to be displaced along the manometer as pressure is increased. (g) Using your biological knowledge and your results draw a suitable valid conclusion related to your aim.
It was predicted that as the distance between the lamp and cabomba sp decreased the distance moved by the NAHCO3 solution in the manometer over 3 minutes would increase. This is because as the distance between the lamp and cabomba sp decreases the light intensiy increases (distance is proportional to light intensity with the equation 1/d^2). Therefore it is fair to assume that as the light intensity increases so would the distance moved by the NAHCO3 solution in the manometer over 3 minutes. As you increase the light intensity more photons of light are absorbed by photosystem II which are then consequently passed on to chlorophyll a in the reaction centre. This causes two electrons to be emitted and raised to a higher energy level before they are then picked up by an electron acceptor. Photosystem II as a result is unstable and requires the electrons that it has lost to be replaced. The process of photolysis provides these electrons and involves the splitting of water into electrons, hydrogen ions and oxygen. Oxygen is a waste product of photolysis and therefore as light intensity increases (proportional to distance between the lamp and cabomba sp), photolysis occurs more as electrons are required to replace the ones displaced from photosystem II, meaning more oxygen is produced as a result. The oxygen produced causes the NAHCO3 solution to be displaced along the manometer as pressure is increased. This explanation matches the trend outlined in my results. Having said this some sets of data do overlap and therefore we cannot be confident that these data sets are significantly different and in fact the true means may be very similar.
Further Work (F)
Plan an investigation using a different independent variable:
(a) Independent variable:
The independent variable for this experiment will be the concentration of NAHCO3 solution, which will be measured in moldm-3. The independent variable range for this experiment would be 0.2moldm-3, 0.4moldm-3, 0.6moldm-3,0.8moldm-3 and 1.0moldm-3.
(b) Two appropriate controlled variable each plus values:
1. The first controlled variable would be the distance between the lamp and cabomba sp which will be measure in cm and maintained at a distance of 15 cm. The distance will be measured accurately using a ruler to ensure this distance is maintained.
2. The second control variable will be the mass of Cabomba, which is measured in grams. With the use of electronic scales I will maintain the mass of the Cabomba at 20grams, which will aid my attempt to standardise the number of chlorophyll molecules there are in each Cabomba sample. This will allow me then to compare my results.
(c) Suggest the expected results of this investigation:
It is expected that as the concentration of NAHCO3 solution increases, the distance moved by the NAHCO3 solution in the manometer over 3 minutes will increase.
