The investigation to find the effect of glucose concentration on fermentation of yeast.

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Planning

Aim;

The investigation to find the effect of glucose concentration on fermentation of yeast.

In this experiment I am going to investigate the fermentation of different Glucose concentration by yeast.  To do this I am going to change the glucose concentration and see how different glucose concentration ferment with yeast. I am going to measure how long it will take the fermentation of yeast to take place, I am going to do this by adding phenolphthalein which is pink when it is alkali to the solution and I am going to measure the time it takes for the phenolphthalein to become colourless which is acidic.

How does it effect the rate and which type of glucose concentration works best?

Glucose -> Ethanol + Carbon Dioxide + Energy (C6H12O6 => 2 C2H5OH +2 CO2 + 2 ATP +heat)

Glucose ethanol + carbon dioxide

C6H12O6 (aq) 2C2H5OH (aq) + 2CO2 (g)

The factor I have chosen is to vary is the concentration of glucose. The concentration will be 1.0M 0.8M 0.6M 0.4M 0.2,M 0.0M

Fair test

 There are many factors that could effect my investigation such as temperature, the volume of yeast and the volume of glucose. To make a fair test I am going to keep this three factor constant, I will also leave the experiment undisrupted during the course of reprising, this mean I won’t stir the substrate.

I also made sure that the thermometers were checked and regularly changed throughout the experiment.  As if I had used the same thermometer during the whole experiment the results would be inaccurate, as I would have to wait for the thermometer to reach the certain temperatures again.

I made sure that I used the same amounts of yeast accurately, so that I could get the most accurate results.  As if we had more or less water in the boiling tube than we should have, the results would obviously be affected, and the experiment would be very unfair.

Upon looking back at the adjustments made, I believe that I am confident in saying that, I made sure that my experiment was as fair as I could possibly make it.

Prediction.

In my investigation I predict that the fermentation of yeast will increase in speed as I increase the concentration of glucose.

As I increase the concentration of glucose, I am increasing the substrate, which will bind to the active site of the enzyme (zymase), which is in the yeast. The rate of fermentation will increase proportionally as the glucose concentration increase but it will eventually stop.

This is a summary of all evidence so far collected to support a prediction.

1. Yeast cell respiration

Yeast cells require glucose for metabolism. They respire it aerobically, then oxidise the ethanol produced. Lack of oxygen causes the build-up of toxic ethanol, which can lead to their death. The larger the population, the greater an effect this will have, leading to the population levelling out as mortality rate increases to mortality rate. This causes the transition from the exponential phase to the stationary phase.

2. The phospholipid bilayer

Yeast cells gain glucose from the medium in which they are suspended, and because glucose is a polar molecule, the rate of its transport across the membrane depends on the availability of hydrophilic protein channels. An increase in glucose concentration has less of an effect at higher glucose concentrations. Therefore, when the rate of reproduction relies on rate of diffusion, it follows the same trend with concentration as facilitated diffusion does.

3. The reproduction of yeast cells

The rate of reproduction can be limited by progress through the cell cycle (in the lag and exponential phases) or, if the level of glucose is low enough, can be limited by the rate at which glucose can be obtained. A higher glucose level could therefore increase the rate of reproduction.

4. Environmental constraints on the population

These, strictly speaking, should include availability of oxygen and glucose and the build up of toxins. Their effect is the same: when the number of yeast cells is sufficient, they have the effect of either putting constraints on the size of the population, or increasing the mortality rate to the natality rate. The effect of either is the levelling-off of the [living population]-[time] graph. A limitation to the experiment arises if one of these other than glucose concentration affects the population growth rate.

5) Stop clock

This is to make sure that all the times are correct therefore no guessing or estimation

Also it can be stopped and the time that the sample is removed from the culture and it can be checked later after one has concentrated on the cell count.

6) Water bath

This is to keep the solution at a constant temperature and to optimise the temperature for of the yeast cells to reproduce so that the limiting factor is the glucose concentration.

7) Concentrations using ratios

This enables me to easily gain highly accurate dilutions of my glucose solution because it to eliminates human error due to taking measurements beyond the accuracy of the measuring vessels or the human eye or using several measuring vessels. The percentage concentrations are irrelevant as these can easily be plotted on a graph afterwards and change anyway when the yeast culture is added. This will reduce the percentage error.

Preliminary Work

Respiration in yeast and the effect of temperature

In an experiment, which we looked at how, temperature affects yeast.  This was done by looking at how much Carbon Dioxide was produced from identical samples of yeast. We measured the CO2 given off in a gas syringe. Then we placed these samples into different water baths, where the water is at different temperature such as 10c, 20c, 30c, 40c, and 50c.

After this we could see from the results that as the temperature increased, the rate at which gas accumulated also increased.  However, when it reached around 40c it slowed down and it was even slower at 50c.  We can see that the temperature is a variable that we will have to control.  By reading (Biology 2) I have found out that the optimal temperature for the yeast to work at is 37c. I am going to do my experiment at 40c.

Conclusions from Trials

Prior to this investigation I carried out a pilot test for the same kind of experiment, but just carrying out one test for each glucose concentrations. But with different amount of glucose, yeast and phenolphthalein.

Although this was a very basic experiment I found that 1.0M of glucose concentration would respire the fastest.  

  • It became apparent that 1cm3 of yeast was not enough and after several trials I found that 4cm3 of yeast worked well. This meant that more of the substrate was needed.
  • The temperature was important in deciding how quickly the yeast would respire and at 40oC a better yield. At higher temperatures the yeast started to stop respiring.
  • Instead of collecting the gas via a measuring cylinder and collecting the CO2 produced I used phenolphthalein to see the color change as an alternative. This was found to be more accurate as I could see the colour change-taking place, and practically it was easier to set up.
  • It was found that the predictions on the rate at which the substrates were respired were correct. The highest Glucose concentration was the quickest.                        
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Apparatus, equipment


Variables

In this experiment I will need to monitor these variables,

  • Temperature
  • Volume of glucose concentration
  • Volume of yeast
  • Volume of phenolphthalein.

In order to make sure that the variable being manipulated is the one making the difference, other possible variables need to be controlled.

Temperature affects both the times required to attain maximum activity and the maximum rate of gas production and the time taken for the color change to take place.

Generally, the gas production rate doubles over a range of 0-40°C. this ...

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