Investigate how temperature affects the rate of anaerobic respiration in a sucrose & yeast solution.

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Investigating the Fermentation of Yeast

Aim:         

To investigate how temperature affects the rate of anaerobic respiration in a sucrose & yeast solution.

Hypothesis:        

Temperature will affect the action of yeast. The rate of respiration will increase with temperature until the heat becomes too much & the enzymes in the yeast are denatured. Very low temperature will slow the rate of respiration & make the enzymes dormant/inactive.

Theory:  

Yeast lives as single cells, its name ‘saccharomyces’ means sugar fungi. It is a fungus which acts as a biological catalyst.

It has been used for many years in the process of fermentation. It is added to rice & barley to produce beer by anaerobic respiration. It is also used in dough, where it ferments in heat with the sugar forming carbon dioxide gas, which therefore causes the dough to rise.

When added to a monosaccharide sugar (e.g.-Sucrose, Maltose, fructose, glucose etc.) it acts as a catalyst speeding up the reaction of anaerobic respiration (fermentation).

The equation for anaerobic respiration is:

Glucose (C6H12O6)  → Energy (ATP) + carbon dioxide (6CO2) + alcohol (2C2H5OH)

It acts as a catalyst due to the enzymes it contains.  Enzymes are substances made of amino acids that join with specific substrates to break them down. They have weak bonds joining them which can be easily broken. High temperature for instance will deform the active site & denature the enzyme.  

They work as follows:

As with all other enzymes the enzymes in yeast are also affected by temperature & pH levels.   I know this from both secondary and first-hand sources.  Earlier in the year, I conducted numerous experiments whilst studying digestion, including investigations of both the action of pepsin and amylase.  

My results were as follows:-

Investigating Temperature and the Action of Amylase:

I set up test tubes filled with amounts of starch and amylase solution and then put each in a water bath, one at room temperature and one at 37ºC.  We then took a sample of solution every minute and tested for levels of starch, using iodine.  My results showed that there was a slight change in levels of starch in the solution at room temperature. However, the change in levels of starch in the amylase/starch solution that was heated to 37ºC showed a much more dramatic change.  This indicated that not only are enzymes affected by heat, but that they also are inclined to catalyse the reaction much more rapidly at higher temperatures.  

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Another experiment shown as an example in the Key Science Biology textbook showed that pepsin (an enzyme that catalyses the breakdown of proteins) works best at around 35ºC and denatures (is destroyed) at temperatures above 50ºC.  

A final experiment I carried out using pepsin investigated the relationship between Ph and the breakdown of protein. It showed that pepsin although did work in neutral conditions was much more effective and efficient in low/ acidic Ph levels.

The results of these experiments allow me to be able to come to the conclusion that enzymes including those in ...

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