Temperature and Photosynthesis

Hypothesis: As the surrounding temperature increases, the photosynthesis rate increases up to a point where further increase in temperature results in a rapid decline in the photosynthesis rate.Photosynthesis is a process through which green plants and other autotrophic organisms produce high-energy, complex food molecules from simpler components, in the presence of light energy (John and Whitehouse 14). During this process, light photons are captured by the electrons within the plant's special pigment molecule. The absorbed light photons excite the electrons within these molecules, which eventually liberate their energy to cell as they fall back to their unexcited ground state (Michael 230). Many cells use this energy to convert carbon dioxide to a carbohydrate. The rate at which photosynthesis occurs therefore depends on the intensity of light and the amount of carbon dioxide it receives, as well as the temperature of its surrounding. In general, an increase in light intensity and the concentration carbon dioxide enhances photosynthesis rate- up to a certain optimal level (Jeffrey, and Enli 25). Additionally, if neither the intensity, not carbon dioxide, nor any other factor is limiting, the photosynthesis rate will increase with rising temperature up to a an optimal level beyond which further increase will result in a rapid decline in the level of photosynthesis (Otto 15).The process of photosynthesis consists of a series of complicated metabolic pathways. Through photosynthesis, light energy is transformed to chemical-bond energy, which is then used to produce complex organic molecules, such as glucose (George and Hademenos 80). The following equation summarizes the chemical reaction photosynthetic organisms use to make ATP and organic molecules:Light energy + water + carbon dioxide → Glucose + oxygen

Light energy + 6H20 + 6CO2 → C6H12O6 + 6O2Ultimately, the energy to power the process comes from the sun. The light capturing event takes place within chloroplast containing chlorophyll and other pigments that absorb specific wavelength of light. Light energy captured by chlorophyll is used to transfer electrons and other electron carriers, the most important being NADP+. It is reduced to NADPH, which is used to reduce carbon dioxide to sugar phosphates in a complex series of reactions (George and Hademenos 81). ATP is also required for photosynthetic reduction of CO2. It is generated by allowing some of the electrons to flow back through an electron transport chain in the membrane. The first stable product from reduction of CO2 in photosynthesis is 3-phosphoglycerate through a process whereby hydrogen is combined with the carbon dioxide (George and Hademenos 82).These reactions are quickened by enzymes; otherwise they would take a long time. Enzymes are protein catalysts that accelerate certain chemical reactions by providing alternative mechanisms in which all energy-of-activation barriers are lower than the original reaction mechanism. The rate of reaction is affected by temperature. Enzymes increase the rate of reaction with increasing temperature, until a temperature is reached which alters the enzymes shape and therefore function (John and Whitehouse 76).For the experiment temperature was the independent variable while air produced by the specimen was the dependent variable. Light intensity and the concentration of carbon dioxide were kept constant, as they were known to affect the rate of the process of photosynthesis. Light intensity was controlled by placing the light source at a fixed position; 10 centimeters away from the experiment set-up. It was also assumed that the concentration of carbon dioxide in the water will remain the same all through the experiment. Care was taken to avoid contact between the electric light source and water.A piece of the specimen was cut and placed in the water beaker. The specimen was anchored with a paperclip to keep it upright. The independent variable-temperature- was adjusted by varying water temperature, which was done by adding up hot water to increase the temperature or ice to cool. The water temperatures were measured using a thermometer and recorded.
The dependent variable -the generated volume of air by the plant- was measured using a photosynthometer and recorded accordingly. The 1mm diameter the photosynthometer tubing was constantly kept submerged to avoid air bubbles forming in it, which will result to imprecise results. The air volume was measured by pulling the syringe on the photosynthometer back noting the air increase on the tubing in length using a rule.

According to a pilot study carried out earlier indicated that a range of 16°Celcius to 32°Celcius will be the best range to use. The pilot study also indicated that the best results will be achieved if the recording was stated straight away, to make use of optimal conditions. At least five variables were needed..

A Table of Results: Air Bubble Length (in mm) Produced At Varying Temperature (in degrees Celsius)Temperature    17.0     21.0     23.0     25.0     26.0     30.01st reading      0.38     0.80     1.56     2.34     3.92     0.38    2nd reading    0.24     1.18     0.80     1.19     3.13     0.223rd reading     0.25     0.78     1.17     1.19     2.36     0.39Average          0.28     0.92     1.18     1.57     3.13     0.34
The first reading was recorded at a 17 ° Celsius temperature. The experiment was replicated three times. The overall results can be said to be reliable as the replicates did give more or less the same readings. However, there seems to be an anomalous result for the 25°Celcius reading, which gave the rate of photosynthesis as 2.34 mm3, as compared to 1.19mm3 per minute obtained from the other two readings. However, other readings were quite consistent.If neither carbon dioxide, light nor any other factor is limiting, the photosynthesis rate increases with rise in temperature up to a point, which further increase in temperature results into a rapid decline in the rate of photosynthesis.  In this experiment, as the temperatures increased, the photosynthesis rate increased up to a point where further increase in temperature results in a rapid decline in the photosynthesis rate. The rate increased steadily from an average 0.28 mm3 per minute at 17 ° C up to an optimal point, beyond which it declines swiftlyOne the more probable mechanisms of this effect are that of an inactivation of enzymes at higher temperatures. The temperature relations are similar to those of photosynthetic reactions (John and Whitehouse 76). Other possible components are the possible destructive effect of relatively higher temperatures upon other constituents of the protoplasm, other than enzymes.  The experiment results supports the hypothesis put forward that as the temperature increases, the level of photosynthesis increases up to a point where further increase in temperature results in a rapid decline in the photosynthesis level. In conclusion, the experiment was a success.

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