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Yeast Experiment

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kdjsodjsdnkkkkndYeast Experiment

Yeast is a single celled fungus (commonly used to ferment alcohol).

Yeast is a facultative anaerobe. This means that it can release

energy from food through anaerobic or aerobic respiration.

Yeast will respire aerobically if oxygen is present use oxygen if it

is present, If it does so; it will break down its respiratory

substrate to release energy for the formation of ATP. The products

of this process are carbon dioxide and water. The equation for aerobic

breakdown of glucose: C6H12O6 + 6O2 6 CO2 + 6 H2O + energy

Yeast will use oxygen if it is present, and break down sugars all the

way to CO2 and H2O. In the absence of oxygen, yeast will switch to an

alternative pathway that does not require oxygen this will produce

ethanol & CO2. The anaerobic pathway is shown below:


Fermentation is the process by which sugar is converted to alcohol

using yeast, this is the anaerobic breakdown of a nutrient molecule

like glucose. This process does no release all energy in the molecule

but allows glycolysis to take place; the pathway of glycolysis is

shown below:

During respiration, high energy carbon bonds are broken. Lower energy

bonds are formed and the difference is released and used to make ATP

from ADP.

Glycolysis splits glucose in to 2 molecules of 3carbon-triose

phosphate, hydrogen is then released and ATP made. From this 2

molecules of pyruvate are made and in total 4 molecules of ATP.

However the net gain of ATP is only 2 molecules as ATP is put in to

the process at the beginning to fuel it. In the absence of oxygen

glucose is broken down in to pyruvic acid but if oxygen is needed to

act as the final hydrogen acceptor to break down the sugar further.

Pyruvic acin then enters the next stages of respiration, which are:

* The Krebs cycle - whereby hydrogen id removes from the pyruvic acid

* The electron transport chain - The hydrogen is used to make ATP

The outcome of this whole process is 6ATP molecules


Metabolism and the breakdown of substances can be measured using the

respiration quotient. The respiratory quotient (RQ) measures the ratio

of the volume of carbon dioxide (Vc) produced by an organism to the

volume of oxygen consumed (Vo). This is represented by the following

equation: Vc / Vo

Enzymes - these are a major part of respiration therefore may affect

the rate of respiration.

Enzymes speed up or catalyse biological reactions within the human

body for example hydrolysis or condensation reactions. During a

reaction the substrate will bind to the active site of an enzyme this

will only occur if it is given some extra energy referred to as

activation energy, in order to start the reaction. In order for a

reaction to take place the substrate needs to collide with the active

site, the speed at which the enzymes collide affects the rate of

reaction as more collisions means a faster reaction, this can be done

by heating. The core body temperature of humans is 37'C which is

generally higher than hat of the surrounding environment this is the

temperature at which reactions take place at a sufficient rate.


Several variables affect the rate of enzyme reaction, the table below

is based on the fact that one variable is altered at a time while the

others remain constant



Enzyme concentration

Initially, reaction rates will increase. This is because there are

more enzyme active sites available to catalyse the reaction. The rate

will slow as the substrate concentration declines. Reaction rate is

faster with higher concentrations but this slows down as the amount of

substrate starts to decline. The more enzymes the more active sites

there are for substrates to slot in to although this depends also on

there being enough substrate once this runs out the reaction will slow

Substrate concentration

Increases the rate of initial reaction but once substrate exceeds the

quantity of the active site the reaction will slow


Reactions are slow at lower temperatures; higher temperatures speed up

the movement of the enzymes and increase the chance of collisions.




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