Photosynthesis Reaction:
Materials and method:
Materials used in this experiment are as follows:
- Syringes.
- Cork borer and rubber stopper
- Beaker
- Light filters [green, blue, red]
- Light source [fluorescent]
-
Sodium bicarbonate [NaHCO3] 0.2% solution
- Broad bean seedlings.
In a nutshell, by the use of vacuum, produced O2 [by photosynthesis] is sucked out of the leaf discs [which were cut from a young broad bean seedling] with no air in the leaves the disc start to sink to the bottom in either a dH2O or a NaHCO3 solution, then a fluorescent light is placed [different or no filters for different groups] so that the discs can once again start photosynthesis. If the photosynthetic reaction is a success O2 will be produced again and the disc will once again surface.
This experiment involves a few variables, one variable which will be varied are the quality of light, chlorophyll best absorbs light in the wavelength range of 400-450 nm [blue light] and 650-700 nm [red light]. Chlorophyll does not absorb green light or yellow light effectively but tends to reflect them, decreasing the amount of light absorbed and decreasing the rate of photosynthesis. Another variable that is varied is CO2 as seen in equation [1] CO2 is a necessity alongside water and light energy, some groups used dH2O while others used NaHCO3, NaHCO3 is actually a source of CO2. Other variables such as temperature, water etc are fixed variable and are tried to be kept at a constant.
Results
The following results were obtained [table 9.1 and fig. 9.2]:
Discussion
The above figure and table clearly prove that the rate of photosynthesis is controlled by many different factors, light and CO2 being the one used. Light quality [nm range] was different for each group, as mentioned before photosynthesis best occurs in the range of 400-450 and 650-700 nm which is blue and red light. No filter would be regarded as the whole spectrum; where not only chlorophyll a and b would kick into action but also beta carotene, phycoerythrin and phycocynanin could also absorb light [ 450 ~ 650 nm]. Clearly only the discs under the red and no filter light responded and the discs underwent photosynthesis thus resurfacing. Therefore one can conclude that quality of light affects the rate of photosynthesis.
Ironically beakers under red and no filter with only H2O did not undergo photosynthesis, while beakers under red and no filter with NaHCO3 underwent photosynthesis and resurfaced as indicated on figure 9.2. Since we already know that NaHCO3 is a source of CO2, therefore one can conclude that not only does the quality of light affect photosynthesis but also the availability of CO2 is essential to the process.
While trying to prove the above to conclusions, there were certainly some errors involved in the process. Some of the major sources of error would be that fact that some of the oxygen which was being produced by the discs was being used by the disc for respiration. Furthermore some of the oxygen produced would have dissolved into the medium the disc was suspended in. Another more unlikely, yet possible error source would be the microscopic animals living on the disc might have used some [very very very minute] oxygen. The light source itself could be regarded as a source of error! The source itself wasn’t the only source in the room, the rooms fluorescent lighting was surely getting to the discs while quantities of photons from other groups would also have reached the discs. Other sources of error would involve the lab partners themselves; while creating the vacuum the index finger may have not fully sealed the chamber thus reaching only partial vacuum; hence not a complete extraction of oxygen present in the discs.
In a nutshell, this experiment proves the equation [1] that both CO2 and light energy both affect the rate of photosynthesis:
In this specific experiment the leaf discs that undergo photosynthesis are the one under the red or no filter with NaHCO3.
