Plan for an experiment - How does temperature affect the rate of photosynthesis?
by
ribbonrebel31 (student)
An investigation into the effects Temperature has on the Rate of Photosynthesis
Aim: The aim of this experiment is to investigate the effect of various temperatures on the rate of photosynthesis by measuring the volume of oxygen produced by elodea.
Introduction: Temperature is one of the main factors that can speed up as well as limit the rate of photosynthesis in plants because it has a direct effect on plant enzymes, which are essential to photosynthesis. Enzymes are globular proteins which act like ‘biological catalysts’, as they’re able to increase the rate of reactions within living organisms by lowering the activation energy needed for a reaction without actually being used up themselves. Enzymes have an active site, which is a region on the surface of the enzyme that substrates bind to and catalyses a chemical reaction. The active sites are specific to certain substrates, as only a few substrates can fit the active site, this is called enzyme-substrate specificity. Enzymes have a small range of temperatures within which they’re able to work. When there’s an increase in temperature, enzyme activity generally tends to double with every increase of 10 degrees, as both the enzymes and substrates have more kinetic energy and are therefore moving faster and having more collisions, which would speed up the rate of photosynthesis. All enzymes have an ‘optimum temperature’, where they’re able to work at their best by having more kinetic energy and collisions, however after the optimum temperature, the temperature tends to be too high for the enzymes to function properly, as their active sites began to denature. For most plant enzymes, the optimum temperature is around 25 degrees C []. When temperature denatures enzymes, the causes vibrations within the enzyme that ends up destroying the shape of the active site by breaking the hydrogen bonds in the enzyme, which would stop it from being able to function properly as it can no longer fit the specific substrate required. This would slow down the rate of photosynthesis. On the other end of the spectrum, if the temperature is too low, enzyme activity would decrease as there’s a decrease in collisions between enzymes and substrates because they have little to no kinetic energy, which would also slow down the rate of photosynthesis.
In photosynthesis, enzymes are prominent in both the light dependent and independent reaction. Ribulose-1,5-bisphosphate carboxylase oxygenase, also known as RuBisCO is an enzyme that’s particularly important in the Calvin Cycle to bond carbon molecules, from carbon dioxide that’s diffused into the stroma, to ribulose molecoles. This is where oxygen is evolved as a by-product of photosynthesis, thus the volume of oxygen that’s produced by the plant can be taken and measured using setting up a photosynthometer to give an accurate indication of the rate of photosynthesis.
My hypothesis for this experiment is therefore that as temperature increases, the volume of oxygen that’s produced by the plant will also increase, as more successful collisions are taking place, with temperatures between 20 - 30
