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. Because the bead will be covered in oxygen bubbles it will start to rise to the surface and stay there. I will time the yeast alginate bead from when it leaves the forceps to when it reaches the surface again.

The reaction is as follows: 2H2O2 2H2O + O2

Equipment needed-

8 x test tubes (20cm3)

90cm3 of hydrogen peroxide (1M)

70cm3 of water

A test tube rack

2 x forceps

A glass rod

5cm3 of yeast

5cm3 of alginate

2 x beakers

150cm3 of calcium chloride

2 x 25cm3 measuring cylinders

Safety precautions-

I will stand up when doing the experiment to avoid spilling hydrogen peroxide on myself, as it is corrosive and can harm skin. I will also wear safety glasses.

I will do 8 different experiments, using 8 different concentrations of hydrogen peroxide. These are the following concentrations I will use-

I will measure these amounts in a 25cm3 measuring cylinder. I will use 2 different measuring cylinders to keep the test fair. As I am varying the concentration of the hydrogen peroxide I will keep the temperature, size of the beads and where the bead is dropped in from the same in each experiment. From my preliminary experiment I discovered that the concentration of hydrogen peroxide is the easiest factor to vary. Another thing I will do to keep it a fair test is to use a different pair of forceps to pick the bead up with and ...

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Prediction

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 reaction is slowed down and cannot increase any further. I predict that as the concentration of the hydrogen peroxide is increased the time taken for the bead to rise to the surface will be less. I predict that if the concentration is doubled the time taken for the yeast alginate bead to rise to the surface will be halved. I predict this because if the concentration is doubled there will be twice as many hydrogen peroxide particles per cm3 of solution so the chance a hydrogen peroxide particle will collide and react with a catalase particle is doubled. So it will take half the time for enough oxygen to be produced to make the yeast alginate bead rise to the surface of the solution. I predict that the time taken for the bead to rise to the surface will be inversely proportional to the concentration of the hydrogen peroxide. So I predict that the rate of the reaction, which is 1/time, will be directly proportional to the concentration of the hydrogen peroxide. 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

Analysing results and drawing conclusions

From my results and from my graph I can see that the rate of reaction is directly proportional to the concentration of the hydrogen peroxide. This is what I predicted. The rate of the reaction increased as the concentration of the hydrogen peroxide was increased. This happened because the higher the concentration of the substrate the more likely the enzyme will collide and successfully react with the substrate so oxygen will be formed more frequently to carry the yeast alginate bead to the surface of the hydrogen peroxide. I also predicted that if the concentration of hydrogen peroxide were doubled the time taken would be halved. I predicted this because if the concentration is doubled there will be twice as many hydrogen peroxide particles per cm3 so the chance a hydrogen peroxide particle will collide and react with the catalase is doubled. So it will take half the time for enough oxygen to be produced to make the alginate bead rise to the surface of the hydrogen peroxide. This did not happen though. The average time taken for the yeast alginate bead to rise to the surface when the concentration of the hydrogen peroxide was 100% was 10.97 seconds and the average time at 50% was 14.75 seconds and at 25% was 20.22 seconds. These results are directly proportional but not how I predicted.

Table of differences

From my table of differences I can see that there is no pattern between the differences.

Evaluation

There are several results that do not fit in with my line of best fit. One of these is when the concentration of the hydrogen peroxide was at 37.5%. The yeast alginate bead took less time to rise to the surface of the hydrogen peroxide than would be expected, this result is anomalous. There are many reasons why this could be. One reason could be that I dropped the yeast alginate bead in higher than the others so it took less time to sink to the bottom of the test tube because it had more potential energy. I might have only done this one time out of the three but it would have an effect on the average. 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.