Why does the rate of respiration slow down and drop when yeast reaches a certain temperature?
Yeast contains enzymes which are needed for anaerobic respiration. Enzymes are sensitive to temperature changes up to a certain temperature and their actions will also increase until this temperature. The reactions that take place in the enzymes will be quicker and so will create more of their products. This optimum temperature is usually around 50 degrees C and once this temperature is reached, the respiration rate starts to slow down and drop. All the enzymes are made up of protein chains of amino acids which exist in the form of a helix structure with hydrogen bonds holding them together. When heat is applied to the enzyme, energy is ‘given off’. The active enzyme cell deforms and the hydrogen bonds break, denaturing the yeast enzyme- it won’t be able to function as usual and is irreversible (this is why it is called denaturing).
