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By Hunarrr1 May 03, 2013 1135 Words
Practical Report:

Background Information:
Hydrogen peroxide (H2O2) is a combination of hydrogen and oxygen. In high concentrations, it can be unstable and even poisonous. In lower concentrations, such as the types found in many homes, it works well as a disinfectant and antiseptic.The reason behind foaming of Hydrogen peroxide is because blood and cells contain an enzyme called catalase. Since a cut or scrape contains both blood and damaged cells, there is lots of catalase floating around.When the catalase comes in contact with hydrogen peroxide, it turns the hydrogen peroxide (H2O2) into water (H2O) and oxygen gas (O2).Catalase does this extremely efficiently -- up to 200,000 reactions per second. The bubbles that can be seen in the foam are pure oxygen bubbles being created by the catalase.Hydrogen peroxide does not foam in the bottle or when in contact with skin because there is no catalase to help the reaction to occur. Hydrogen peroxide is stable at room temperature.

Enzymes are global proteins that act as catalystto biochemical reactions in living cells. A catalyst alters the speed of a chemical reaction without itself undergoing any permanent change. An enzyme is a biological catalyst that increases the rate of chemical reaction by lowering the level of activation energy necessary to start the reaction. Enzymes speed up these reactions by bringing the reactants into close proximity and facilitating their interaction. Liver contains a specific enzyme called catalase. Enzyme molecules have a small region that is functional, called the active site. In an enzyme-catalyzed reaction, the substrate binds to the active site and forms enzyme-substrate complex with the enzyme. The enzyme then breaks the bonds in the substrate. The product ofthe reaction then leaves the enzyme, which remains unchanged after the reaction. Catalase in an enzyme produced by our liver to break down hydrogen peroxide – a common end product of metabolism, but highly toxic if accumulated in the body – into water and oxygen. The equation of the reaction is: 2 H2O2 --- O2 + 2 H2O

In this experiment, hydrogen peroxide will be used as a solution. Liver will be a source of catalase. In this case, hydrogen peroxide will act as substrate, the enzyme will be catalase, from the liver. During the reaction, the enzyme molecule and substrate molecule will undergo a reaction, breaking hydrogen peroxide into water and oxygen. Oxygen will be given of as gas and foam will be formed.

Dependent variable:
Amount of foam produced by the reaction after 30 seconds
-The stopwatch is started as soon as the liver is dropped into the measuring cylinder -The stopwatch is stopped after 30 seconds and the amount of foam produced in measured

Independent variable:
-Concentration of hydrogen peroxide solution
-Hydrogen peroxide solutions of different concentrations are prepared by adding different volumes of water to of 6% hydrogen peroxide solution.

Controlled VariablesHow variables will be controlled in the experiment Enzyme concentrationenhances the rate of reaction because there are a greater number of active sites accessible for the enzyme-substrate complex to be formed TemperatureRate of reaction increases as the temperature increases, the enzyme may start to denature. The rate of reaction increases because enzymes and substrate have more energy permitting them to move around more rapidly, resulting with more collisions. Volume of Hydrogen PeroxideControlling the volume of hydrogen peroxide solutions ensures that the same amount of hydrogen peroxide molecules is available for reaction in the test tube.

Amount of LiverMaking sure that you are using the same amount of liver for the experiment. Variations in sizes will affect the volume of foam produced. Pouring out everythingMaking sure that everything is poured out of the test tube, the foam or any pieces of liver. If not, it may affect the outcomes of the next experiment. Replacing the lid onto Hydrogen PeroxideHydrogen Peroxide breaks down into hydrogen and water if the lid on the bottle is left open. If that occurs, reaction might not be as accurate.

-Wear appropriate goggles and safety jacket.
-Work in centre of table with plenty of space.
-Work standing up and with chairs under tables and not in the way. -Do not eat or drink anything in a laboratory. If you are not careful you could end up in severe trouble in case you happen to ingest anything that causes you harm. -Always ensure that you wear proper fitting clothes and nothing that is too loose. You should also wear your lab coat to avoid spilling anything on your clothes. -Usually there are approved safety goggles that are worn while working in the lab. These safety glasses protect anything from entering your eyes.

-100cm³ measuring cylinder
-10 cm³ measuring cylinder
-2 teat pipettes
-Stop watch
-Sharp knife
-Solutions of hydrogen peroxide with concentrations 6%, 4%, 2%, 1%, 0.5% -10 cm³ detergent
-Fresh liver
-100cm³ distilled water

-Use the knife to cut up 10 pieces of liver, approximately 1cm x 1cm x 1cm -Use the pipette to get the hydrogen peroxide from the bottle to 10 cm³ measuring cylinder. Try to get exactly 4cm³ of hydrogen peroxide, make sure to read the meniscus at eye level in order to get an accurate reading -Carefully pour the hydrogen peroxide into the 100cm³ measuring cylinder, then add 2 drops of detergent using the pipette -Use the forceps to pick up one piece of liver and carefully drop in into the 100cm³ measuring cylinder, with hydrogen peroxide and detergent -Have a stopwatch handy, as soon as the liver is dropped into the solution, start the time -After 30 seconds, measure the amount of foam produced using a ruler - Repeat this procedure at least 5 times with the concentration of hydrogen peroxide provided to the group

Focused Question:
To investigate the effect of substrate concentration (manipulated by increasing concentration of hydrogen peroxide) on the rate of enzyme activity of catalase from liver, testing the rate of decomposition of hydrogen peroxide in the given time (30seconds). The volume of foam can be used as a measure of enzyme activity.

The higher the concentration of hydrogen peroxide, higher the amount of foam produced in 30 seconds. Hydrogen peroxide will act as substrate, the enzyme will be catalase. The more the concentration, more of the substrate is available from the catalase to act on, breaking down more hydrogen peroxide quickly in short time and therefore create more foam.


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