INVESTIGATION INTO THE EFFECTS OF USING DIFFERENT RESPIRATORY SUBSTRATES ON THE RATE OF ANAEROBIC RESPIRATION OF YEAST

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Haris Ali

A2 Biology Coursework

INVESTIGATION INTO THE EFFECTS OF USING DIFFERENT RESPIRATORY SUBSTRATES ON THE RATE OF ANAEROBIC RESPIRATION OF YEAST

INTRODUCTION

Yeasts are single celled organisms like bacteria, their name saccharomyces means `sugar fungi`, but unlike fungi they do not grow hyphae.

Yeasts are commonly found wherever sugar occurs. It has been used for thousands of years to ferment sugar into ethanol i.e. alcohol. Yeast added to dough ferments the sugar in the dough to produce carbon dioxide. This makes the dough rise.

 Aerobic respiration releases far more energy than anaerobic respiration, this is because it completely oxidises glucose into carbon dioxide and water.

Reducing sugars such as glucose and fructose are readily oxidised. When this reaction occurs the sugars lose electrons to another substance, which is said to be reduced.

Some disaccharides are not easily oxidised, notably sucrose, these types of sugars are non-reducing.

Monosaccharides combine by a condensation reaction, and they can be turned back into their single units by hydration. When yeast acts upon a disaccharide it converts it to a monosaccharide so it becomes easier to oxidise. This suggests that it will take longer; therefore the dissacharrides will have a slower rate.

Sucrose is made up of fructose and glucose, and lactose is made up of glucose and galactose.

The higher the temperature the faster the reaction will be up until the optimum temperature is reached. So the yeast culture should be stored at a high temperature to obtain the best results.

C6H12O6        2CO2 + 2C2H5OH

The rate at which carbon dioxide is produced can be used to measure the rate of anaerobic respiration of yeast.        

PROCEDURE

Apparatus:         12 fermentation tubes

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        12 test tubes

        Pipette

        Stopwatch

        Test tube rack

        Glucose, fructose, sucrose and lactose

        Water bath

        Yeast

Plan:

  1. You will be provided with a yeast culture already set up. It will be labelled A (glucose) B (fructose) C (sucrose) and D (lactose) and contained in a water bath to allow fermentation to begin.
  2. Using a pipette transfer culture A into three fermentation tubes, make sure it goes right to the top of the tube. We are doing it three times to ensure we have enough results to do the t-test
  3. Insert the fermentation tubes into test tubes ...

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