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In this case, the concentration is measured in ml. The different concentrations of alcohol taken into consideration are – Mol, 1 ml, ml, ml, ml, and ml. Dependent – Rate of yeast fermentation (in number of CO bubbles released) With an increase in the concentration of alcohol, the rate of fermentation of yeast will decrease. This is because when the alcohol concentration goes above the yeast cell’s tolerance the yeast cells die. Also, alcohol denatures the enzymes responsible for the break down of simple sugars i. E the food supply of yeast, as a result of which the yeast cells die.

With a decrease in the rate of fermentation, the amount of CO released will also decrease and so the number of CO bubbles released will decrease with an increase in alcohol concentration. The CO bubbles released are an indicator of the fermentation rate. Bubbles were counted manually by releasing it under water for 5 minutes measured using a stopwatch. The rate of bubbles released were calculated and analyses. Controlled -Temperature of alcohol and water in the beaker (in CO) Temperature of the alcohol and water used affects its activity on the yeast cell.

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The higher the temperature, the higher the possibility of the yeast cell dying. Thus the temperature of alcohol and water was kept constant at ICC measured by an alcohol thermometer with uncertainty В± 0. C by performing the experiment in an air conditioned laboratory. Volume of yeast + glucose solution in the bottle (in ml) The volume of yeast taken in the bottle is kept constant so that the number of yeast particles stays the same in all the cases ( i. E with Mol, mm’, ml, ml, ml, and ml alcohol concentration).

If in any case the volume of yeast used is more, the number of yeast particles reacting with alcohol will increase as a result of which more yeast cells will die and the rate of fermentation will decrease. The volume of yeast taken in the bottle was 30 ml, measured with the help of a wringer with uncertainty Time duration of the experiment (in minutes) The time for which the bottle with yeast and Mol to ml alcohol is inserted in the beaker with water is kept constant. This is because when the time duration for which alcohol and yeast reacts is varied, the rate of fermentation will be altered.

The time is kept constant by using a stopwatch with uncertainty В± 0. 01 s to measure 5 minutes during which the experiment will take place. Materials required 1 X 500 ml beaker Bottle for yeast Tap water Stopwatch (В± 0. 01 s) 1 X ml Beaker for alcohol solution Beaker with Yeast + glucose solution Syringe (В± 0. 1 ml) Alcohol thermometer (В± 0. 1 CO) Method Take a mall beaker and fill it with mall tap water at room temperature ICC measured using an alcohol thermometer.

Submerge the bottle containing yeast and glucose solution (first with no alcohol) completely into the beaker filled with water. Once the bottle is submerged into the beaker filled with water, bubbles start emerging. The first 5-8 bubbles are air bubbles. After letting them go, start counting the bubbles for 5 minutes using a stopwatch. Repeat steps 3 and 4 with 1 ml, ml, mi, ml and ml of alcohol contained in the bottle filled with yeast. Note down the number of bubbles released and notice the decrease in bubbles as the concentration of alcohol is increased.

Set up of experiment DATA COLLECTION TRIAL 1 Concentration of Alcohol (ml) Number of bubbles released 18 TRIAL 2 24 TRIAL 3 45 26 TRIAL 4 TRIAL 5 37 32 2 6 3 5 4 DATA PROCESSING AVERAGE OF ALL TRIALS 44 7 Graph Analysis of the graph From the graph we see that the number of bubbles released decrease with the increase in alcohol concentration. There is a decrease in the number of bubbles released from 44 at Mol to 24 at Mil and 7 at 2 ml. After this, it goes from 6 at ml o 4 at ml and ml. This shows that there is a decrease in the fermentation of yeast as the alcohol concentration of yeast is increased.

If the concentration of alcohol was increased further, the fermentation process would have come to a stop eventually. CONCLUSION From THE observations, we see that there is a decrease in number of bubbles released with the increase in the concentration of alcohol, i. E. The fermentation of yeast decreases. This occurs because, with an increase in alcohol concentration, more yeast cells die, and more enzymes responsible for the breakdown of simple sugars die. As simple sugars constitute the food supply of yeast cells, their unavailability results in the death of yeast cells.

Thus, this supports the hypothesis made initially. EVALUATION Sources of error As the initial bubbles are air bubbles, it is difficult to know when exactly the CO bubbles are released. This would have led to errors in the calculation of the number of bubbles. Even though the beaker was kept at room temperature, there might have been a slight fluctuation in the temperature as a result of which the number of bubbles released may have varied. It is possible that the beaker, test tube or the thermometer was calibrated inaccurately as a result of which the readings taken would vary.

In addition to this, the volume of yeast solution, and alcohol used might not have been accurate due to uncertainties and reading errors. Methods of improvements The beaker could have been insulated using wool or cloth in order to ensure better consistency in temperature as a result of which the bubbles released will not vary. Performing the experiment more number of times and taking the average would have reduced the random errors. BIBLIOGRAPHY 1 . Allot, Andrew. “The Chemistry of Life. ” B Study Guides – Biology for the B Diploma. ND De. Oxford UP, 2007. 20.

Print. In an experiment, the independent variable is the variable that is varied or manipulated by the researcher, and the dependent variable is the response that is measured. An independent variable is the presumed cause, whereas the dependent variable is the presumed effect. The IV is the antecedent, whereas the DVD is the consequent. In experiments, the IV is the variable that is controlled and manipulated by the experimenter; whereas the DVD is not manipulated, instead the DVD is observed or measured for variation as a presumed result of the variation in the IV.

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