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Biology Investigation : Yeast-Alginate

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Biology Investigation : Yeast-Alginate Plan: I plan to investigate the rate at which the enzyme catalase (found in yeast) breaks down hydrogen peroxide into water and oxygen. There are many factors I could vary in this experiment but I have chosen to vary the concentration of the hydrogen peroxide. I will make beads of yeast alginate by mixing 5cm3 of yeast (which contains catalase) and 5cm3 of alginate and stir thoughly with a glass rod. I will allow drops of yeast alginate to fall off the end of the glass rod into a small beaker of calcium chloride. I will make 50 beads and pick out 24 which are 5mm in diameter with forceps (I will measure them using graph paper). I will then drop a yeast bead into the substrate (hydrogen peroxide) where it will react. The yeast alginate bead will fall through the hydrogen peroxide (20cm3) to the bottom of the test tube. When the bead gets to the bottom of the test tube the catalase in it will start to breakdown the hydrogen peroxide into water and oxygen. As it does this oxygen bubbles start to from on the surface of the bead as it is a product of the breakdown of hydrogen peroxide. ...read more.


I predict that if the concentration of the hydrogen peroxide is too small the bead will not rise to the surface. I predict this because in a low concentration there are a very small number of reacting particles in the solution and not enough to breakdown into oxygen to carry the yeast alginate bead to the surface. This diagram would result in one successful collision. But the diagram underneath in which the concentration of the hydrogen peroxide is doubled two successful collisions will occur. This diagram helps me explain my prediction. The substrate (hydrogen peroxide) and the catalase molecules are continuously on the move. Every so often they will collide so that the substrate molecule(s) fits into the enzyme?s active site. Enzymes work best when they have a high enough substrate concentration for the reaction they catalyse. If too little substrate is available the rate of the reaction is slowed and cannot increase any further. Obtaining evidence Volume of hydrogen peroxide (cm3) Volume of water (cm3) % hydrogen peroxide Time taken (secs) 1st experiment Time taken (secs) 2nd experiment 20 0 100 11.13 10.39 17.5 2.5 87.5 12.01 12.16 15 5 75 12.74 12.74 12.5 7.5 62.5 12.89 13.34 10 10 50 14.69 14.95 7.5 12.5 37.5 14.96 15.66 5 15 25 19.11 20.53 2.5 17.5 12.5 30.98 36.72 Volume of hydrogen peroxide (cm3) ...read more.


Another anomalous result is when the hydrogen peroxide was at 87.5% concentration. The yeast alginate bead took more time to rise to the surface of the hydrogen peroxide than would be expected by looking at the line of best fit. There are many reasons why this could be. I may have dropped the bead in lower than the other beads so it took longer to reach the bottom of the test tube because it had less potential energy. Another reason might be that the bead I picked for that particular experiment might have been smaller than the rest so had less of the enzyme catalase in it so took longer to breakdown the hydrogen peroxide. If I were to do the experiment again I would definitely repeat the results more times to minimise the effect errors have on the average and use more concentrations of hydrogen peroxide to make the results more accurate and reliable. Further work I could do to provide additional evidence for my conclusion would be to investigate different catalysts / enzymes e.g manganese (IV) oxide and compare the results and the graphs to the results and graphs I got by using yeast alginate beads as a catalyst. I could also use different forms of catalase e.g liver. I could find out if the curves of the graphs are the same or these sort of results just happened for this catalyst / form of catalyst. ...read more.

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