BIOLOGY PRACTICAL-yeast and gas production

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Yeast and Gas production

Planning (a)

Aim: To investigate gas production by yeast in a glucose mixture.

Theory: The process by which living organisms release energy from their food is called respiration. It is the oxidation or break down of glucose molecules to release energy. Respiration can be of two types Aerobic and Anaerobic. During Aerobic respiration glucose is burnt in the presence of oxygen to produce energy and carbon dioxide. However in Anaerobic respiration glucose is burnt in the absence of oxygen to produce energy and alcohol or lactic acid (animals). Yeast cells respire anaerobically to produce ethanol and carbon dioxide. Yeast cells have enzymes which are used in this process, Zymase enzymes.

        Enzymes are biological catalysts that alter the rate of reaction without being chemically changed during the reaction. They help to speed up the bio-chemical reactions in living organisms. Enzymes are substrate-specific. That is a particular type of enzyme only catalyses few reactions. This means that there are very less possible substrates that can combine with the active site of the enzymes. The active site of an enzyme is the region on the surface of an enzyme to which the substrates bind and are catalyzed by the enzyme. This active site has a particular shape and different chemical properties. Only the few possible substrates with the right shape and the chemical properties are attracted towards the active site and bind together to be catalyzed. This is often referred to as the lock and key mechanism.

 the food substances.

                

                                                An Enzyme

A graph showing the rate of enzyme activity against temperature:

Enzymes speed up biological reactions by reducing the activation energy required and hence enabling the reaction to take place more readily.

The enzyme activity is dependant on temperature. At a low temperature the enzyme activity is slow, as the substrate molecules collide with the enzyme molecules less frequently. As the temperature increases the molecules vibrate faster and collide more frequently. This increases the rate of reaction as now more substrate molecules bind with the free active site and are catalyzed. However, as the temperature further increases >60˚C, the vibrations and the frequency of collisions increases, however the enzymes start to become denatured. At very high temperature the increases vibrations in the enzyme molecules break the bonds and the active site is lost. When this happens the enzyme is said to have denatured that is: lost its shape so that it can no longer perform its functions.

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Hypothesis:

It is known that yeast respires anaerobically in a glucose mixture to produce carbon dioxide gas and alcohol (Ethanol-C6H5OH). This process is catalyzed by enzymes. Thus the rate of gas production will be the highest when the enzyme activity is maximum. The optimum temperature that is the temperature at which the enzymes work the fastest is around 40˚C-45˚C. Therefore this is the temperature at which the rate of respiration will be the fastest. At a low temperature (<20˚C) the rate gas production will be slow as the enzyme activity is slow. At a very high temperature (>60˚C) ...

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