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How to plan an experiment - First, make sure you know what you're trying to find out. In this case, it is...To measure the optimum temperature for respiration in yeast.

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How to plan an experiment First, make sure you know what you're trying to find out. In this case, it is... To measure the optimum temperature for respiration in yeast. There is absolutely no point in stating this again as the "aim" or "introduction". It merely wastes time, paper, ink and effort. What you should do first, however - before launching into a detailed description of how or why - is OUTLINE the procedure to be used so that the reader has some idea what is going on. You could include the diagram (which, if complete will get you P4b) at this stage. Something like this: Outline A sample of yeast will be suspended in glucose solution in a boiling tube. The carbon dioxide produced by respiration will be bubbled through water and the rate of bubbling used as a measure of the rate of respiration. ...read more.


Controlled: CONCENTRATION OF GLUCOSE SOLUTION. With more glucose available, the yeast will respire faster. Therefore the same concentration of glucose solution - 1g of glucose dissolved in 20cm3 water - will be used for all runs of the experiment. CONCENTRATION OF YEAST SUSPENSION. If there are more yeast cells present in the mixture, more carbon dioxide will be given off and the rate of respiration will seem to be higher. Therefore the same concentration of yeast suspension - 2g of dried yeast in 20cm3 water - will be used for all runs of the experiment. DIAMETER OF NOZZLE. A smaller nozzle will produce more bubbles for a given volume of gas and therefore appear to make the rate of respiration greater. The same nozzle will therefore be used for every run of the experiment. This lot will score P6a(ii). Then, describe the steps necessary to carry out the experiment. ...read more.


5. Repeat this measurement for a second minute to improve reliability. 6. If necessary, repeat again. 7. Wash out the tube containing the yeast suspension/glucose solution and repeat the whole experiment at the next higher temperature. 8. Continue in this way until the experiment has been carried out at all temperatures listed above. In practice, you won't have time to do seven runs in succession, leaving each for 10 minutes to start bubbling. Instead, you can set up two or three at intervals of three minutes in separate water baths. 9. Calculate the mean rate of respiration at each temperature and plot this against temperature. Stating this lot gets you P2 and P4a(i). Explaining why each step is carried out thus gets P6a(i). Now it's quite clear what's going on, you can make your prediction of the results (P4a(ii)) and explain the scientific reasoning behind it. (P6a(ii)) "It says so in the book" or "It seems likely" are NOT scientific reasoning ! ...read more.

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