Plan:
Firstly I will include my background knowledge about making immobilised yeast cells;
- Using a syringe, put 4cm³ of sodium alginate in a beaker.
- Put 6cm³ of yeast suspension to the sodium alginate and mix well.
- Draw the mixture into a syringe.
- Add this mixture into a solution of calcium chloride in another beaker.
When these beads are made add ten beads to an 8% sugar solution. Do two at a time to find an average.
Repeat at room temperature, 30º, 40º, 50º, and 60º. To record the results count to ten minutes and record how many beads have risen. Also when the first bead rises, this time will be recorded. The results are recorded like this to try to prevent anomalies For example if nine beads rise in ten minutes then one is an anomaly and we can recognise this.
The controlled variables are kept constant throughout the tests to insure a fair test is carried out. All tests are carried out twice for added accuracy and therefore an average can be made.
A problem with this experiment is the fact that water temperature will not remain constant for any length of time. The water baths could be left to cool and assume that all experiments cool at the same rate but this could lead o inaccuracies when working out optimum temperatures. So I will keep topping up the water baths to try to keep the temperature constant.
Risk assessment
The main risk in this assessment is the fact the fact that we will be using very hot water. When filling up beakers and boiling tubes we must be extremely careful in order not to burn ourselves.
The yeast cells can also be irritable if they get in eyes, so some care must be taken when using these cells.
Diagram
Results
Analysis
From my results you can see that the basic relationship is that as the temperature gets higher it takes less time for the beads to rise.
The graph shows the relationship as a negative correlation. The graph is not a straight line; this is because the temperature does not increase at a proportional rate to the time taken for the yeast balls to rise. This is explained in the conclusion. The graph dips at 45º and then goes up again afterwards.
For the basic results it does not prove or disprove my prediction. At room temperature, 21º it took 26 mins 38 secs for the balls to rise. Whereas at 50º the beads took an average of 5 mins and 21 secs to rise.
There is one result which clearly does not fit the pattern, this is the result at 60º C. The beads did not rise at all in this case.
Evaluation
There are various ways in which my results could have been improved. As a whole my results appear very reliable. This is shown by a good graph of results.
The 60º C result was not anomalous, as I will explain in the conclusion.
A way I think I could have improved my results is by the way I recorded my results. This was a very important aspect of this experiment as timing was the input variable and the experiment was dependable on it. If I recorded the number of beads that rose per minute then there would have been a more accurate set of results, the graph would have looked better.
There was in fact one anomalous result that occurred at 45ºC when only 9 of the ten yeast balls rose. This is because I think the materials we are dealing with a biological cells and organisms. They do not have a set way of reacting and behaving. In nature there are always things that do not fit the trend.
A way in which I could carry my experiment further is to carry out experiments at every degree not every ten degrees this would allow me to find the optimum temperature that the cells respire at and the temperature at which the cells denature. The reason why this is not possible is the fact that with the laboratory equipment that we have keeping temperature constant to a single degree is nearly impossible due to the water losing its heat so rapidly.
Conclusion
My prediction was proved correct with my experiment. The cells did respire more efficiently up to a certain temperature and then denature. A problem with my prediction is that it stated that at forty degrees the cells would denature but the results and graph showed that the cells denatured at 45 degrees C. This is what the dip in the graph has shown.
This could be for various reasons, the most likely reason is that the cells did not actually experience temperatures of those stated. The water in the water bath would lose heat before it reached the beads, this is due to temperature travelling through the glass and losing heat energy on the way.
An alternative explanation for this is the beads were not subject to these temperatures because they were insulated by other beads surrounding them.
The added test of the beads at 45ºC was a very beneficial us. It enabled us to find out the optimum temperature that the beads respired at. It also enabled us to work out the temperature at which the beads denatured; this was a temperature around the 45ºC area. We cannot say for sure due to the cooling baths losing heat energy and the insulating properties of the beads.
Up to the forty five-degree point the yeast balls respired more efficiently at a higher temperature, this was due to the increased energy the particles were given. My prediction was proved mainly correct.
