MCA Test Preparation Part 4

Hydrogen peroxide (H 2 O 2 ) is a highly active chemical often used for cleaning minor wounds. Hydrogen peroxide is also naturally produced in cells within your body. Because it is toxic to your cells, hydrogen peroxide will kill your cells if not immediately removed or broken down. Recently, students conducted an experiment to compare the effect of two substances which break down hydrogen peroxide. One of the substances, manganese dioxide (MnO 2 ), is an inorganic catalyst. A catalyst is a chemical that initiates or speeds up the rate of a chemical reaction without being consumed in the reaction. The other substance, catalase, is an enzyme found in the liver of animals. An enzyme is a protein that acts as an organic catalyst. The catalase found in your liver breaks down H 2 O 2 in your body so your cells are not harmed. At the end of the experiment, the students concluded that both catalase and manganese dioxide were equally effective in breaking down hydrogen peroxide. In order to further the investigation, two students prepared an experiment to find out if increasing the surface area of the piece of liver would increase the rate of reaction between catalase and hydrogen peroxide.

1. (1 pt.) Before conducting the experiment, the students stated that the catalase enzyme found in liver will react more readily with hydrogen peroxide if the liver is ground up in a mortar and pestle. This statement is a: a.Conclusion b.Hypothesis c.Law d.Theory Supplies needed for the experiment: Calibrated test tubes Beef Liver Manganese Dioxide (powder) Hydrogen Peroxide (liquid) 250 ml beaker Hot Plate Test Tube Tongs Mortar and Pestle Conclusion: a statement about your hypothesis based on experimental data Hypothesis: an educated explanation for a set of observations prior to experimentation Law: a statement of fact that is generally accepted to be true and universal and is meant to describe, in concise terms, an action or set of actions. Theory: a well-tested explanation that is generally accepted to be true and universal and that unifies a broad range of observations and hypotheses.

To begin the experiment, the students mixed 2 ml of hydrogen peroxide with a 1 cm x 1 cm piece of liver. After watching the reaction they measured the amount of bubbles produced within their test tube and recorded their results in Table 1. In step two of the experiment the students took another 1cm x 1 cm piece of liver and ground it up in a mortar and pestle before mixing it with 2 ml of hydrogen peroxide. Again, they measured the amount of bubbles produced within their test tube and recorded their results in Table 1. TABLE 1 ReactantsResults of Reaction bubbles measured (ml) Liver and 2 ml H 2 O 2 moderate5 Ground Liver and 2 ml H 2 O 2 strong8

In another part of the room, two more students were conducting another experiment using the same supplies. These students were trying to find out if heating the liver would have any effect on the results. To begin this experiment the students took a 1cm x 1cm piece of liver, placed in a test tube, and heated it over a water bath until it was fully cooked. They then mixed the cooked liver with 2 ml of hydrogen peroxide. They measured the amount of bubbles produced within their test tube. They recorded their results in Table 2. TABLE 2 ReactantsResults of Reaction bubbles measured (ml) Heated Liver and 2 ml H 2 O 2 none0

2.(1 pt.) In each of the experiments the students always used a 1cm x 1cm piece of liver and 2 ml of H 2 O 2. Please explain why it was necessary to remain constant among all the experiments. Scientific experiments are designed to test only one variable to see if this variable is having an impact on the outcome. If you test more than one variable, you don’t know which one is having more of an impact.

3. (2 pts.) Create a bar graph from the information provided in both Table 1 and Table 2 and choose the title, x-axis, and y-axis labels from the list below. a.Amount of bubbles released in ml b.Reactants used c.Reactants vs. Bubbles Produced Reactants: Liver and H 2 O 2 Ground Liver and H 2 O 2 Heated Liver and H 2 O 2 a. Amount of bubbles released in ml b. Reactants used c. Reactants vs. Bubbles Produced 2 / 2: Student correctly labeled the graph and correctly graphed the results. 1 / 2: Student correctly labeled the graph but didn’t correctly graph the results. 1 / 2: Student correctly graphed the results but didn’t label the graph correctly.

4.(1 pt.) Why did heating the liver (and catalase enzyme) result in no reaction? Enzymes are proteins and proteins lose their shape when they are boiled. Once they lose their shape, they no longer work. 5. (1 pt.) The students want to know what is in the bubbles produced from the reaction between MnO 2 and H 2 O 2. To help them answer this question they construct a simple equation for the reaction. Use the following reactants and products to complete a balanced equation for the reaction. HINT: remember that MnO 2 is a catalyst! Reactant and Products: H 2 O, O 2, H 2 O 2 2 H 2 O 2 2 H 2 O O 2 + MnO 2 Products Reactant