Enzyme: Hydrogen Peroxide and Ph Essay

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Stage 2 Biology: Completion Practical
Experiment: Enzyme rate of reaction
Introduction:
An enzyme is a natural catalyst which is made up of protein. Enzymes speed up chemical reactions without altering the products of the reaction and without being altered itself. Yeast contains the enzyme catalase. It is involved in the following equation which causes the breakdown of Hydrogen Peroxide into water and oxygen:

Hydrogen Peroxide Water + Oxygen

2H2O2 H2O + O2

When we immerse small discs of filter paper into the yeast suspensions and then drop them into our solution of hydrogen peroxide, a reaction occurs. This reaction involves bubbles being produced that are attached to the filter discs and these bubbles force them to rise to the surface of the solution.

Aim:
To test that pH levels affect the activity of catalase in yeast.

Hypothesis:
If yeast covered filter discs are dropped into different solutions of Hydrogen Peroxide, then a rate of reaction will occur consisting of gas being produced.

Variables: Independent: pH levels of Hydrogen Peroxide Dependent: Rate of reaction of catalase Constants:

Apparatus: * * Hole puncher (5 mm) * Yeast suspensions (7-10g/100g) * 50 mL Measuring Cylinder * Stop watch * Thermometer * Labels for beakers * Solutions of Hydrogen Peroxide (pH 3, pH 7, pH 9, pH 11) * Safety equipment (safety glasses and lab coats) * Filter paper * Forceps * Distilled water (warm) (100 mL) * 0.1% hydrogen Peroxide * Pipette * Beakers

Method: 1. Prepare a yeast suspension by adding about 7g of dry yeast to 100mL of warm distilled water (about 300c). Allow yeast to expand by having the suspension sit aside for 10 minutes. 2. Measure 40mL of 0.1% hydrogen peroxide solution into a small beaker (100 mL). Pour solution into beaker just under 40mL and then using a pipette, add droplets until 40mL is reached on the meniscus level. (You will need to get on an ‘’eye level’’ to achieve this step). 3. Use a hole puncher to cut 30 discs from the filter paper. Avoid touching the discs to prevent contamination. 4. Using forceps, dip a single disc into the yeast suspension. Shake off excess liquid and then place into the hydrogen peroxide solution. Start the stop watch as soon as the disc reaches the bottom of the beaker. Record how long it takes for the disc to rise to the surface in a table. 5. Repeat this technique 5 times. Repeat steps 2-4 using varying pH solutions. Results: Table 1.1: Rate of reaction of catalase (yeast) in different pH levels of Hydrogen Peroxide solutions.

| Time taken | for discs to | Rise in pH | Solutions of | H2O2 (secs) | Trial Number | 0.1% H2O2 | pH 3 | pH 7 | pH 9 | pH 11 | 1 | 45.3 | 3.94 | 6.53 | 0.9 | 2.50 | 2 | 30.9 | 3.62 | 4.43 | 0.9 | 1.69 | 3 | 30.3 | 2.38 | 0.5 | 0.9 | 2.18 | 4 | 70.1 | 2.78 | 0.97 | 0.9 | 2.44 | 5 | 24.1 | 1.28 | 1.97 | 0.9 | 3.31 | Average time taken for discs to rise (secs) | 40.14 | 2.8 | 2.88 | 0.9 | 2.42 | Rate of Reaction (sec-1) | 2.4 x 10-2 | 3.6 x 10-1 | 3.5 x 10-1 | 1.11 | 4.1 x 10-1 | Observations: There were a few observations that were made throughout the experiment. One that was very obvious was when the reaction occurred, bubbles formed around the small filter discs. These bubbles mean that a gas is being produced and this gas is oxygen. Graph:

Figure 1.1: The effect of pH levels on rate of reaction on catalyse. Discussion: From Figure 1.1, the results suggest that the optimum level of pH for catalase 11. The bell curve of my graph is convex and in contrast to what would normally be expected to support the concepts that enzymes have an optimum pH. (It should increase until an optimum is reached, then decrease). Random errors are caused by any
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