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Investigating the Effect of Glucose Concentration On the Rate of Reproduction of Yeast Cells

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Introduction

INVESTIGATING THE EFFECT OF GLUCOSE CONCENTRATION ON THE RATE OF REPRODUCTION OF YEAST CELLS Prediction In this section I will look at all the factors involved in the rate of reproduction of yeast cells, bring them together at the end of the section and deduct a scientific conclusion as to what I would expect to happen. Yeast Cell Respiration Yeast cells, like any other organism, need a substrate to respire. Respiration in general In respiration, they use the substrate to produce ATP for cell metabolism. The overall equation for respiration using glucose is: C6H12O6 + 6O2 � 6CO2 + 6H2O Figure 1: Aerobic respiration in detail Therefore, the more glucose available, the greater the rate of respiration and the easier it is for cell metabolism to take place. The more detailed version of the respiratory pathway is shown in Figure 1. However, one cannot merely assume that a greater rate of respiration can occur with a higher level of glucose concentration because it is a living organism involved. This means that high levels of glucose concentration could cause the yeast cells to become crenated and therefore the reproductive mechanisms would not function because of the physiological strain caused by the low pressure potential. This would mean that the initial rate of reproduction would be much less than that of cells in solutions of glucose concentrations on the limit of the cell's pressure potential. However, this need not be a worry because I will not use glucose of such a high concentration. Also, because it is an organism, other factors like waste products and method of uptake need to be taken into account. These are discussed below. Glucose catabolism in yeast In the case of yeast, something else also needs to be considered. This is that it is an anaerobe. This means that yeast cells first respire the glucose anaerobically and then break down the ethanol produced to manufacture ATP aerobically using the available oxygen in the solution. ...read more.

Middle

These are calculated in step 8) � This can also be calculated later � This calculates the doubling time in 105 seconds. 11) Run one additional experiment with 0.57143% (30/40) glucose, taking a cell count every thirty minutes. Record the results for this in the time/population table Reasons for apparatus These are the explanations for each choice made above. 1) 100cm3 conical flask with cotton wool plug I chose this because it holds larger volume than a test tube/ boiling tube and sits easily in the water bath. The cotton wool plugs prevents gas exchange. 2) Haemocytometer This is the most accurate way of measuring cell content of the solution: actually counts the number one in a precise volume. Other methods of population measurement would be: density of solution, change in mass and changes in the acidity of the solution due to increase in carbon dioxide concentration. These are all indirect ways of measuring population growth. The haemocytometer method actually measures the amount of yeast cells per unit volume. It also involves taking a small sample out, rather than having to measure the mass/density of the whole solution, which would mean removing the entire experiment from of the water bath, which would disrupt the rate of or reproduction. 3) Slide with cover slip The cover slip makes sure that the correct volume is on the slide and that the cells are visible (in focus). 4) 1ml pipette This is most accurate for measuring out the 1ml of yeast solution needed. This is because it is graduated to a higher degree of accuracy than a wider measuring vessel could be - if the lines are closer together it is harder to get the level in the pipette exactly right and if the same difference in height corresponds to the smaller volume, the effect of human error is reduced. This reduces the percentage error for yeast solution added 5) ...read more.

Conclusion

The rate of diffusion therefore curves off at higher concentrations. See Figure 2. Comparison to prediction My prediction was: " During the times for which I plan to run my experiment, I only expect to see the period from the lag phase to the end of the exponential phase. Not many cells will be dying during these initial phases (although possibly a few during the lag if they do not successfully adapt), so the total count will be approximately equal to the living population. The rate of growth will therefore follow the pattern: " I ran my experiment for longer than I had planned. The culture therefore reached the beginning of the stationary phase. The first sentence was therefore probably a correct estimation. The prediction of the rate of growth in relation to the concentration of glucose was supported by my results. I can therefore conclude that my results did support my qualitative prediction and the rate of population increase does follow the pattern of facilitated diffusion rate. Evaluation In this section I will consider the values from the standard deviation test and the number of anomalies, and decide how confident I can be that the results were not purely by chance. The values obtained are shown on the last column of the table. The greatest standard deviation from the average is 39% at 0.784% glucose. This, however takes the results that I called anomalous into account- hence the high value. Apart from this, the highest value is 30%. This is not very high considering that this is the deviation of the raw data. There were few results that seemed to vary significantly to be recognised as anomalies. These were all mentioned earlier. More generally, my results are fairly consistent, as well as being consistent with the prediction, which is an indication that they are reliable. Some of the finer points of the progress of the population with time remain to be conclusively proven, but the primary quantitative prediction as to the effect of glucose concentration on the rate of reproduction appears to be conclusively and reliably proven. ?? ?? ?? ?? ...read more.

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