Rate Of Photosynthesis And Respiration

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A study that uses Spinacia oleracea to show that oxygen is produced by photosynthesis and consumed at the same time by respiration. An oxygen electrode recorded the concentration of oxygen in the chamber, throughout each stage of the experiment. This was used to calculate the rate of photosynthesis and respiration.


Photosynthesis is the most important process on earth. It provides the energy for photoautotrophs to make their food for heterotrophs and is an anabolic process (Reece et al, 2015). Photosynthesis occurs in the chloroplasts. Photons hit the chlorophyll molecules surrounding the Photosystem II complex and excite them. Two electrons and transported into plastoquinone Qb from Phostosystem II and these are replaced
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Rate of oxygen production and rate of photosynthesis of S. oleracea in response to varying light intensities. To calculate the rate of photosynthesis, the rate of oxygen production in the dark is added to the measured rate of oxygen consumption at each light level. The rate o photosynthesis increases rapidly originally and plateaus at full light intensity. These results were taken from Workstation 1 & 2.


As light intensity increased, so did the measured rate of oxygen consumption and photosynthesis in S. oleracea, in a linear fashion until a plateau was reached. This is due to the fact that the rate of photosynthesis is dependent on light, and if the light intensity is not increased, then the rate of photosynthesis cannot increase.

Before CO2 was added to the reaction, photosynthesis occurred at a slower rate because carbon dioxide is a reactant in the photosynthesis equation and by adding CO2, this increases the reactant available to produce glucose and oxygen. With a low supply of CO2, this reaction occurs much more
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At the light compensation point the rate of photosynthesis is equal to the rate of respiration and this occurs at a light intensity of 40 µmoles photons/m2 /s1. At this point the chloroplasts are producing glucose and oxygen at the same rate as the mitochondria are breaking down these reactants into CO2 and water, to produce ATP to drive the cell’s reactions(Reece et al, 2015). At 0 light intensity, no photosynthesis is occurring and oxygen is being consumed; this is due to aerobic respiration.

The results of this study show that an increase in light intensity will increase the rate of photosynthesis until full light intensity is reached. It also shows that while plants release oxygen through photosynthesis, they also need it for respiration and hence oxygen is consumed while also being produced. They use the oxygen for aerobic respiration, a catabolic reaction, which uses glucose and oxygen to form carbon dioxide and water and releases

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