How Does Robert Hill Find The Rate Of Photosynthesis
Introduction
Photosynthesis takes place in the chloroplast and is the use of sunlight energy for cell processes. It happens through a number of chemical reactions and the transfer of electrons. It is used as the source of energy (ATP) for plants. The reaction equation for photosynthesis is
H2O + CO2 + (Light) (CH2O)N + CO2
In the Hill reaction, Robert Hill showed how chloroplasts in water can still function if there is light and an electron acceptor to release oxygen. He proved that the oxygen in photosynthesis comes from water instead of carbon dioxide, which had previously been the consensus. He also demonstrated the difference between light-dependent (“photo”) photosynthesis and light-independent (“synthesis”) photosynthesis (Stegenga, …show more content…
2016). The light-dependent reactions happen in the thylakoid and the light-independent reactions happen in the stroma (Hogan, K., Reece, J. B., Dickey, J. L., Taylor, M. R., Simon, E. J., & Campbell, N. A., 2015) The experiment also showed that photosynthesis’ oxidation-reduction reactions, which are initiated by light, are necessary for photosynthesis to occur. It proved that there is a conversion from light energy to chemical energy. The light-dependent part of photosynthesis is used to reduce NADP+ which forms NADPH. NADP+ is reduced by the acceptance of more electrons, it can be oxidized from NADPH by the loss of electrons. This process can be seen with the use of DPIP (blue) dye. The dye changes color based off if there is photosynthesis, which would involve the transfer of electrons so the rate and effectiveness of photosynthesis at different variables can be shown with this dye.
Based off of the Hill experiment, our new experiment was the comparison of photosynthesis rates in spinach, romaine lettuce and purple lettuce. It was designed around the idea of the use of light and a spectrophotometer to measure the rate of photosynthesis. The spectrophotometer is used to measure the amount of light that goes through a solution and the amount of light that is absorbed. It measures the percent transmittance of the solute of chloroplast solution that was used. In that experiment, the dependent variable was the percent transmittance of each tube. The independent variable was the different leaves so the different chloroplasts used in each tube. The hypothesis was that out of the unboiled chloroplast samples of each, the spinach would have the highest level of transmittance because if it has a darker green then that pigment would have a higher rate of photosynthesis. Based off of the Hill experiment data, it would seem that the spinach had a high percent of transmittance so it would also have a high rate of photosynthesis.
Methods and Materials
Our experiment used a similar solution to the one that was used in the Hill experiment. Each of the chloroplast solutions was made from spinach, romaine lettuce, or purple lettuce that had been under lamp light for 10 minutes. The lamp was used to stimulate photosynthesis by providing light energy. They were put in a pre-chilled blender and beaker so that the proteins are not denatured by heat. Sucrose (0.5M) is added to the blender, water is not added because it would affect the chloroplast by putting it in a hypotonic solution, causing the chloroplast to swell and possibly burst. It was then blended at three 10-second intervals so that there would not be much exposure to heat that could denature the proteins if they were blended for longer intervals. Once filtered through a cheesecloth to filter out the still large pieces of leaves, some of the solution is kept at the same temperature and some is boiled for each type of leaf. Each tube contained 1ml of buffer solution, 3ml of water, 1ml of DPIP and 3 drops of either chloroplast or unboiled chloroplast. There is also a tube for calibration for each type of chloroplast used to balance the spectrophotometer. There was 4mL of water in the calibration tube, no DPIP and 1mL of buffer put in along with 3 drops of each respective type of chloroplast. Each tube should have had a total of 5mL of liquid. The control for type of chloroplast solution was the boiled solution since the proteins needed for the process of photosynthesis would be denatured by the heat, allowing that to be the control since there should be no process of photosynthesis able to function. Labeled transfer pipettes were used to put together the entire solution for each tube and then the tubes were covered with Parafilm and inverted to mix all the liquids together. They were placed by a lamp in a test tube rack to continue the photosynthesis reactions however there was a flask filled with water placed between the tubes and the lamp which created a heat sink so that the tubes would get the light energy but would not be effected by the heat given off from the lamp. The percentage of transmittance was tested at five minute intervals, 0, 5, 10, and 15 minutes, using the spectrophotometer that was set at 605nm for measuring wavelengths in photosynthesis. The calibration tube was used before each test to reset the spectrophotometer and Kimwipes were used to ensure that there were no fingerprints or other things that could disrupt the data collection. We collected data on the percent of transmittance on a table at each time interval and for each trial we first used the specified calibration tube, then the unboiled tube, then the boiled tube. The relationship between percent of transmittance and the rate of photosynthesis is that if there is a greater percent of transmittance then there is a greater rate of photosynthesis. This is important in showing if there is an increase or decrease or constant in the process speed of photosynthesis. That allows us to see which chloroplast would be more effective in producing energy for cell processes and allows us to compare the differences in rate for the chloroplasts.
Results The results of our experiment showed that the unboiled spinach had the highest rate of transmittance, 1.3667, compared to the unboiled romaine lettuce and unboiled purple lettuce.
The rate was still calculated for each experimental tube. It is important to calculate the rate because if one experimental value stays at a relatively high constant rate yet another changes from a low value to a high value then that won’t be shown unless the rate of each is taken. The rate is able to show the change in values rather than just the individual values of the data. It is calculated by the change in percent of transmittance over the change in time. There were some unexpected results in our data. For example, the boiled purple lettuce had a higher rate of transmittance than the unboiled purple lettuce. That would be expected to be the opposite since the boiled chloroplast would have denatured proteins. Figure 1 displays the increase or decrease in the percent of transmittance for each tube over the 15-minute test period. It shows the relationship between the unboiled and boiled purple lettuce, where the boiled purple lettuce had a higher percent of transmittance than the unboiled purple lettuce. Also, the unboiled romaine lettuce had a negative rate of transmittance which would mean that there were less photosynthetic processes happening over time. Figure 2 displays that the unboiled spinach had the highest rate of transmittance by about 0.9734, boiled purple lettuce had the second greatest rate of transmittance. It also shows how boiled spinach and boiled romaine lettuce had decreases in rate of transmittance yet boiled purple lettuce had an increase in the
rate.
Discussion
The data that was gathered during this experiment is a bit contradictory to the thoughts that we had before this experiment. For example, the increase in light that the chloroplast is exposed to over time would seem to increase the rate of photosynthesis reactions however with the unboiled romaine lettuce the rate decreased. There could have been slight errors in reading the spectrophotometer, the exact amount of time each tube was given before the transmittance percentage was taken again, and also with inconsistencies in the control tubes, that could have a negative effect on the validity of our data. The control, boiled, tubes for both spinach and purple lettuce had increases in the percentage of transmittance. That was an odd encounter in our data since the proteins should have been denatured by the heat which would cause for a decrease in photosynthetic reactions, not an increase. This experiment could be modified so that data is produced clearly and could be used to find the differences on a wider scale of pigmentations of chloroplast. That information could be used to know which plants are more effective at taking in carbon dioxide and producing oxygen at a faster rate than others, which could be useful in environmental science. Overall, the spinach did have a higher percent transmittance so the hypothesis can be partially supported however we cannot draw conclusions as to if there is a correlation between that and the dark pigmentation of the spinach chloroplast and the rate of photosynthesis since there are inconsistencies in the data we gathered. The different chloroplast solutions had lower rates of photosynthesis for the lighter pigmentations of the romaine and purple lettuce and the spinach, which had a darker pigmentation, had a higher rate of photosynthesis. The control seemed to not work as a textbook control since there were still increases in the photosynthetic processes. For it to have been a valid control, the rate of photosynthesis should have remained constant or decreased from the original measurement.
Photosynthesis takes place in the chloroplast and is the use of sunlight energy for cell processes. It happens through a number of chemical reactions and the transfer of electrons. It is used as the source of energy (ATP) for plants. The reaction equation for photosynthesis is
H2O + CO2 + (Light) (CH2O)N + CO2
In the Hill reaction, Robert Hill showed how chloroplasts in water can still function if there is light and an electron acceptor to release oxygen. He proved that the oxygen in photosynthesis comes from water instead of carbon dioxide, which had previously been the consensus. He also demonstrated the difference between light-dependent (“photo”) photosynthesis and light-independent (“synthesis”) photosynthesis (Stegenga, …show more content…
2016). The light-dependent reactions happen in the thylakoid and the light-independent reactions happen in the stroma (Hogan, K., Reece, J. B., Dickey, J. L., Taylor, M. R., Simon, E. J., & Campbell, N. A., 2015) The experiment also showed that photosynthesis’ oxidation-reduction reactions, which are initiated by light, are necessary for photosynthesis to occur. It proved that there is a conversion from light energy to chemical energy. The light-dependent part of photosynthesis is used to reduce NADP+ which forms NADPH. NADP+ is reduced by the acceptance of more electrons, it can be oxidized from NADPH by the loss of electrons. This process can be seen with the use of DPIP (blue) dye. The dye changes color based off if there is photosynthesis, which would involve the transfer of electrons so the rate and effectiveness of photosynthesis at different variables can be shown with this dye.
Based off of the Hill experiment, our new experiment was the comparison of photosynthesis rates in spinach, romaine lettuce and purple lettuce. It was designed around the idea of the use of light and a spectrophotometer to measure the rate of photosynthesis. The spectrophotometer is used to measure the amount of light that goes through a solution and the amount of light that is absorbed. It measures the percent transmittance of the solute of chloroplast solution that was used. In that experiment, the dependent variable was the percent transmittance of each tube. The independent variable was the different leaves so the different chloroplasts used in each tube. The hypothesis was that out of the unboiled chloroplast samples of each, the spinach would have the highest level of transmittance because if it has a darker green then that pigment would have a higher rate of photosynthesis. Based off of the Hill experiment data, it would seem that the spinach had a high percent of transmittance so it would also have a high rate of photosynthesis.
Methods and Materials
Our experiment used a similar solution to the one that was used in the Hill experiment. Each of the chloroplast solutions was made from spinach, romaine lettuce, or purple lettuce that had been under lamp light for 10 minutes. The lamp was used to stimulate photosynthesis by providing light energy. They were put in a pre-chilled blender and beaker so that the proteins are not denatured by heat. Sucrose (0.5M) is added to the blender, water is not added because it would affect the chloroplast by putting it in a hypotonic solution, causing the chloroplast to swell and possibly burst. It was then blended at three 10-second intervals so that there would not be much exposure to heat that could denature the proteins if they were blended for longer intervals. Once filtered through a cheesecloth to filter out the still large pieces of leaves, some of the solution is kept at the same temperature and some is boiled for each type of leaf. Each tube contained 1ml of buffer solution, 3ml of water, 1ml of DPIP and 3 drops of either chloroplast or unboiled chloroplast. There is also a tube for calibration for each type of chloroplast used to balance the spectrophotometer. There was 4mL of water in the calibration tube, no DPIP and 1mL of buffer put in along with 3 drops of each respective type of chloroplast. Each tube should have had a total of 5mL of liquid. The control for type of chloroplast solution was the boiled solution since the proteins needed for the process of photosynthesis would be denatured by the heat, allowing that to be the control since there should be no process of photosynthesis able to function. Labeled transfer pipettes were used to put together the entire solution for each tube and then the tubes were covered with Parafilm and inverted to mix all the liquids together. They were placed by a lamp in a test tube rack to continue the photosynthesis reactions however there was a flask filled with water placed between the tubes and the lamp which created a heat sink so that the tubes would get the light energy but would not be effected by the heat given off from the lamp. The percentage of transmittance was tested at five minute intervals, 0, 5, 10, and 15 minutes, using the spectrophotometer that was set at 605nm for measuring wavelengths in photosynthesis. The calibration tube was used before each test to reset the spectrophotometer and Kimwipes were used to ensure that there were no fingerprints or other things that could disrupt the data collection. We collected data on the percent of transmittance on a table at each time interval and for each trial we first used the specified calibration tube, then the unboiled tube, then the boiled tube. The relationship between percent of transmittance and the rate of photosynthesis is that if there is a greater percent of transmittance then there is a greater rate of photosynthesis. This is important in showing if there is an increase or decrease or constant in the process speed of photosynthesis. That allows us to see which chloroplast would be more effective in producing energy for cell processes and allows us to compare the differences in rate for the chloroplasts.
Results The results of our experiment showed that the unboiled spinach had the highest rate of transmittance, 1.3667, compared to the unboiled romaine lettuce and unboiled purple lettuce.
The rate was still calculated for each experimental tube. It is important to calculate the rate because if one experimental value stays at a relatively high constant rate yet another changes from a low value to a high value then that won’t be shown unless the rate of each is taken. The rate is able to show the change in values rather than just the individual values of the data. It is calculated by the change in percent of transmittance over the change in time. There were some unexpected results in our data. For example, the boiled purple lettuce had a higher rate of transmittance than the unboiled purple lettuce. That would be expected to be the opposite since the boiled chloroplast would have denatured proteins. Figure 1 displays the increase or decrease in the percent of transmittance for each tube over the 15-minute test period. It shows the relationship between the unboiled and boiled purple lettuce, where the boiled purple lettuce had a higher percent of transmittance than the unboiled purple lettuce. Also, the unboiled romaine lettuce had a negative rate of transmittance which would mean that there were less photosynthetic processes happening over time. Figure 2 displays that the unboiled spinach had the highest rate of transmittance by about 0.9734, boiled purple lettuce had the second greatest rate of transmittance. It also shows how boiled spinach and boiled romaine lettuce had decreases in rate of transmittance yet boiled purple lettuce had an increase in the
rate.
Discussion
The data that was gathered during this experiment is a bit contradictory to the thoughts that we had before this experiment. For example, the increase in light that the chloroplast is exposed to over time would seem to increase the rate of photosynthesis reactions however with the unboiled romaine lettuce the rate decreased. There could have been slight errors in reading the spectrophotometer, the exact amount of time each tube was given before the transmittance percentage was taken again, and also with inconsistencies in the control tubes, that could have a negative effect on the validity of our data. The control, boiled, tubes for both spinach and purple lettuce had increases in the percentage of transmittance. That was an odd encounter in our data since the proteins should have been denatured by the heat which would cause for a decrease in photosynthetic reactions, not an increase. This experiment could be modified so that data is produced clearly and could be used to find the differences on a wider scale of pigmentations of chloroplast. That information could be used to know which plants are more effective at taking in carbon dioxide and producing oxygen at a faster rate than others, which could be useful in environmental science. Overall, the spinach did have a higher percent transmittance so the hypothesis can be partially supported however we cannot draw conclusions as to if there is a correlation between that and the dark pigmentation of the spinach chloroplast and the rate of photosynthesis since there are inconsistencies in the data we gathered. The different chloroplast solutions had lower rates of photosynthesis for the lighter pigmentations of the romaine and purple lettuce and the spinach, which had a darker pigmentation, had a higher rate of photosynthesis. The control seemed to not work as a textbook control since there were still increases in the photosynthetic processes. For it to have been a valid control, the rate of photosynthesis should have remained constant or decreased from the original measurement.