Effect of Changes in Substrate Concentration on the Reaction Rate of an Enzyme

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Effect of changes in substrate concentration on the reaction rate of an enzyme

IB biology Internal Assessment
3/23/12

Research Question: Effect of changes in substrate concentration amount on the reaction rate of an enzyme Introduction: In this experiment, the substrate is hydrogen peroxide. The purpose of this investigation is to find out the relationship between the substrate concentration and the rate of reaction. Substrates are molecules that are acted upon by enzymes. For instance, amylase, an enzyme found in saliva, helps break down complex starch molecules (substrates) into smaller sugar molecules (products). In other biochemical reactions, substrates require assistance of specific enzymes to form new products. When the amount of enzyme stays constant, the substrate concentration will determine the rate of reaction. However, when the number of substrate molecules exceeds the available number of enzyme, the rate of reaction will no longer increase, but stay constant. If there is a constant amount of enzyme, as the concentration of a substrate increased, the rate of reaction will increase as well. This is because of molecular collisions. If you have more reactant molecules, there are more to collide. Aim: The effect of hydrogen peroxide on the enzyme activity of catalase Hypothesis: When the amount of enzyme stays constant, the substrate concentration will determine the rate of reaction CONTROLLED VARIABLES| Units| Possible effect(s) on results| Amount of enzyme | 2.8g| an extra drop of enzyme can alter the rate of reaction | Size and type of test tubes | 30ml| The size and type of test tubes were constant, because they can alter the pressure | | Units| Range|

INDEPENDENT VARIABLE | Hydrogen Peroxide (Substrate) Concentration | ml| 5,10,15,20,25,30| DEPENDENDENT VARIABLE| Rate of Reaction | Seconds| 80 secs| VARIABLES:

METHOD FOR CONTROLLING VARIABLES:
CONTROLLED VARIABLES| Method for control:|
1. Amount of enzyme| All liver used were at a constant weight of 2.8g | 2. Size of test tube | All test tubes were 30ml|

METHOD FOR COLLECTING DATA:
1. Prepare a tube rack and place 6 30ml tubes in them.
2. Weigh liver at a constant 2.8g.
3. Place the 6 pieces of liver into the test tubes.
4. Obtain 3% hydrogen peroxide and a graduated cylinder.
5. Pour 5ml into test tube 1, 10ml into test tube 2, 15ml into test tube, 20ml into test tube 4, 25 ml into test tube 5, 30ml into test tube 6 (but not at once one after the another) . 6. Once hydrogen is in the test tube start the stop watch to see how long it will take to react. 7. Repeat the action in no. 5 & 6, six times for each tube. 8. Observe what happens to the liver while reacting to the hydrogen peroxide. 9. Clear up the station and pour liver into a waste beaker. 10. Clean each of the test tubes out and put the materials away. The materials used in this experiment are:

I. 50-ml graduated cylinder
II. Fresh liver
III. 6 test tubes (30 ml)
IV. 3% Hydrogen peroxide
V. Disposable Pipettes
VI. Stopwatch
VII. Digital scale
VIII. 50ml beaker
IX. Test tube rack
X. Plastic knife
XI. Scissors
QUALITATIVE DATA.
The reaction started as soon as Catalase touched the surface of hydrogen peroxide. More concentrated hydrogen peroxide produced more oxygen bubbles and the reaction rate was faster. As more substrate was added the reaction was faster. Once the 5ml of hydrogen peroxide was put into the test tube with the liver, the reaction rate was slow. As the amount of hydrogen peroxide increased the reaction became faster. When putting the 15ml of peroxide into the test tube 3 during the first trial the reaction bubbles spilled into tube 4 affecting the result slightly, because it made it to start reacting before the 20ml of peroxide was put into test tube 4 . In test tube 6 during the first trial the liver was lifted from the surface about 2cm....
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