Investigate how temperature affects the rate of reaction of the enzyme catalase on its substrate hydrogen peroxide.

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Aim

To investigate how temperature affects the rate of reaction of the enzyme catalase on its substrate hydrogen peroxide.

Scientific Background

Enzymes are biological catalysts which increase the rate of reactions by lowering the activation energy needed for the reaction to tale place. The activation energy is the amount of energy needed for molecules to react when they collide. Molecules need to collide in order to react, this is known as the collision theory. When they collide they may not react as a certain amount of energy is required to break bonds, this energy is the activation energy.

Enzymes are made of a long amino acid chain, within this some molecules are attracted to each other, so the chain folds in on itself to form a 3D shape.




How enzymes are shaped.


An area on the surface of the enzyme is known as the active site. This is where reactions take place to form or break down substances. Enzymes are specific which means a particular enzyme only works on one substance known as its substrate. For example, the substrate of amylase is starch and the substrate of lipase is fats. They only have one substrate because the active site is formed in a different shape for each enzyme, where only one substance can fit. The 'lock and key' hypothesis states that the enzyme is like a lock which will only have one key.

'Lock and Key' hypothesis

The substrate shown is the only substance that fits the enzyme. An enzyme substrate complex is the compound formed when the substrate is attached to the active site, it is only in this form for a short time while the substrate is being broken down.

Enzymes can break own substances, known as catabolism, or can join substances together, known as anabolism. Together they form metabolism which is every chemical reaction in the body.

catabolism and anabolism.

Enzymes are affected by four factors which are

1. Temperature

2. pH

3. Enzyme concentration

4. Substrate concentration

A temperature increase gives ore energy to gives more energy to the substrate and the enzyme so they are more likely to collide and react. The frequency of the collisions with the right activation energy will increase so the rate of reaction will increase. The rate of increase is shown by a mathematical coefficient known as Q10, which states that a ten degree rise in temperture will cause the rate of reaction to approximately double. However at high temperatures enzymes will begin to denature. This means the attractions holding together the shape of the enzyme will begin to break so the active site loses its unique shape and is unable to react with its substrate. The optimum temperature for most enzymes is 37?C, after this they begin to denature. The enzymes in the body have this optimum temperature and the body has adapted to control its temperature so the enzymes are working at there best.

Enzymes also have an optimum pH level, where they work best, any changes to this level will cause the enzymes to begin to denature.


Pepsin works best in acidic conditions because it is used in the stomach along with stomach acid. Lipase works best in alkali conditions because it works with bile in the intestines.

Increasing the concentration of either the enzyme or the substrate will increase the number in the solution meaning there is more chance of collisions and reactions. There is a limit to the rate of reaction. For example if the enzyme concentration is increased from the same concentration of enzyme and substrate then the rate of reaction will not increase as there are not enough subsrate molecules to react with.

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Hypothesis

I predict that a rise in temperature will cause a rise in the rate of reaction until 40?C, after which enzymes will denature so the rate will fall. This will happen because a rise in temperature will mean the are moving faster and are more likely to collide with the catalase on the potato resulting in a greater frequency of collisions. A higher temperature will also mean more hydrogen peroxide molecules will have an energy above the activation energy, so there will be more collisions with the right activation energy. This will result in the rate of reaction increasing.

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