ray ban aviator plastic

[sonyaany]

Effect of substrate concentration on rate of activity of the enzyme catalase

HypothesisI believe that as the concentration of the hydrogen peroxide (substrate) decreases, the rate of reaction will decrease consequently. This is because there will be fewer collisions between the substrate and enzyme molecules (catalase in yeast) because there are fewer molecules of hydrogen peroxide, so there will be a decrease in enzyme substrate complexes formed. The reaction will then stop because all of the active sites become saturated with substrate because the enzyme is the limiting factor. This will result in a decreased volume of oxygen being produced as one of the by products of this reaction.

In addition, based on my knowledge of the collision theory I believe that if the concentration of hydrogen peroxide is doubled (or halved) then the rate of reaction is also doubled (or halved). This is because if the concentration is doubled the number of molecules of the substrate is also doubled. This means there will be twice as many successful collisions. Therefore it is true to say that in theory: rate concentration.

Preliminary workI have done some preliminary work and as a result, have identified problems that may occur in my main investigation, such as timing, measuring and keeping variables that I am not investigating constant, (such as temperature etc).

In the main procedure I will control the temperature in a water bath in order to create a constant external temperature to dissipate the heat energy. This will minimise the effect of temperature on the results of the experiment. I have decided to do this because in my preliminary procedures, I used a thermometer to measure the temperature of the hydrogen peroxide (when left on the side) at different intervals, and on different days, and found that the temperature of the hydrogen peroxide fluctuated slightly.

By doing this, it will ensure that the test is as fair as I can make it. Although the reaction is exothermic and will give out heat during the reaction anyway, since the heat has been dissipated by being kept in the water bath, the amount of heat given off in the experiment will be relative to the concentration of hydrogen peroxide, but obviously some reactions will take longer than others, so more heat will be produced. However the temperature initially will be kept the same in each case.

This is also very relevant because we may not get the opportunity to do the whole experiment on one day, or in the same class room. This means the room temperature in each class room or on different days will not be the same for each procedure, because of obvious factors such as type of day (very cold or mild etc) and the level of heating within the class rooms.

Temperature directly affects the shape of the active site. At a temperature below the optimum, the molecules have less kinetic energy so the rate of collisions between enzyme and substrate molecules are low and therefore less enzyme substrate complexes are formed. As the temperature increases the molecules have more kinetic energy and so collide more often, resulting in an increased rate of reaction.

Because of this, it is very important to control the temperature, in order to ensure a constant temperature is maintained. Above the optimum temperature, the thermal energy breaks the hydrogen bonds holding the secondary and tertiary structure together, so the active site changes shape and eventually the reaction can no longer be catalysed.

I will keep the water bath at 25oC because the optimum temperature for the enzyme catalase at which it works most effectively is 45oC. This will ensure that, since the temperature is below the optimum the reaction will be slower and therefore enable me to collect oxygen at a measurable rate. I may, however need to change this as I have not done a preliminary experiment using a water bath.

In my preliminary work I also found that when doing the experiment with 1g of yeast, and 5cm3 of 20 volumeof hydrogen peroxide, the rate of reaction was too fast to collect oxygen at a measurable rate, and therefore made it impossible to gain meaningful results. I consequently reduced the mass of yeast to 0.2grather than the 1.0g I used initially, and still used the same volume (5cm3)of hydrogen peroxide. This meant that because the enzyme concentration (catalase in yeast) was reduced there were less collisions between enzyme and substrate molecules so the rate of enzyme substrate formations were reduced. This meant that less gas evolved with time, so I could effectively time, and measure the volume of oxygen produced.

Another factor which I had to consider was the surface area of the yeast granules, because each yeast granule has a different surface area the amount of enzyme will differ in each granule, but more importantly the greater the surface area of the yeast the more reactions take place because of the fact that there will be more collisions between the enzyme and substrate molecules.

In my first preliminary experiment I just weighed 1.0g of yeast as it was supplied in its granule form. However in my next preliminary experiment, I decided this would be unfair in the main procedure and because of this I decided to grind the yeast into a powder so that the surface area would be more similar in each yeast granule.

Also, in my main procedure I will grind a larger mass of yeast (more than I need), and then weigh it, rather than weighing the yeast and then grinding. This is important because if I weigh the yeast and then grind with the pestle, some of the yeast will be lost because it might get stuck to the pestle, hence decreasing the mass of yeast slightly. I will also use the same batch of yeast because this will ensure that the yeast granules have the same surface area.

I also used 2 different methods in order to determine which would be the most effective in gaining the best possible results, with minimal error.

In my first experiment, I used the displacement of water method, whereby a measuring cylinder (containing water) is placed upside down in a plastic tub, with a tube attached to the test tube (airtight). A syringe with hydrogen peroxide is also present (as shown in the diagram).

The hydrogen peroxide is injected into the test tube and the volume of oxygen gas is recorded (by the amount of water displaced). This would determine the rate of reaction. However I decided against this method for several reasons. Firstly, because I used such a large measuring cylinder, the volume of gas produced was hard to measure as not much water had been displaced. Although I could have used a smaller measuring cylinder, I decided that the best possible way I could do the experiment was by measuring the volume of gas directly using a gas syringe, rather than by the displacement of water. Also, because the hydrogen Ray Ban Sale peroxide had to be inserted into the syringe before the reaction could begin, the amount of time it would be out of the water bath (which I intend to use in my main experiment) was longer than necessary. I decided that I could reduce this time by using a different method.

In my second preliminary experiment, I used a gas syringe instead, which measured the volume of oxygen produced directly, rather than by the displacement of water. The hydrogen peroxide is Ray Ban Sale inserted into a 5cm3 small beakerand then tipped over to "spill" the contents and start the reaction. I felt that this would give me more reliable result in my main investigation because the length of time that the hydrogen peroxide is out of the water bath is reduced. Furthermore, the volume of gas is measured directly. I noticed that when doing the first method that "bubbles of gas" were affected by people bumping the table, and that sometimes they got trapped in the tube, so even though the product of the reaction (oxygen) had been formed it was not measured until afterwards, (at a later stage in the reaction). Also, the bubble volume is affected by the diameter of the tube and the overall pressure of the water (depth of the water) so I believe that by using the gas syringe, I will be able to eliminate this inaccuracy as water will not be involved. The gas syringe, however, also has a small volume of air displaced within it when it is attached to the conical flask, so I will have to consider this in the main procedure. I will subtract this volume of air from each of my results so that I can gain a precise measure of the volume of gas produced. every 5, 10, 15 seconds etc). In my first preliminary experiment the reaction went to fast to collect oxygen at a measurable rate, but in the second preliminary experiment I measured the volume of gas every 10 seconds, but found that the reaction was over before I had enough measurements and that the results I gained would not be sufficient to obtain enough results and make a valid conclusion. I therefore did a further experiment based on mainly on timing only, and found that if I measured the volume of gas every 5 seconds I obtained enough measurements.

However, I do have to take into account that I will be using different concentrations of hydrogen peroxide in my main experiment, so 5 seconds may not be sufficient to measure the volume of oxygen produced in the slower reactions and I may need to change this.

The concentrations of hydrogen peroxide I will use will be 100%, 90%, 80%, 70%, 60% and 50%. I will use these concentrations because I believe that if I were to go any lower than 50% that the rate of reaction will be relatively slow, and will not produce enough results because the substrate concentration (hydrogen peroxide) will be too low in concentration. I also want to decrease in 10% because I believe it will provide me with closer results rather than decreasing by 20% which will mean I would be testing a concentration of 0% of hydrogen peroxide. Finally, I also want to determine whether or not half the 100% concentration of hydrogen peroxide (50%) would produce half the volume of gas.

independent variableThe independent variable will be the factor that I am going to manipulate. This will be the concentration of the hydrogen peroxide. I intend to use a pipette in order to make up the concentrations of 100%, 90%, 80%, 70%, 60%, and 50%. I will do this by making each mixture up to 100cm3, so for example, the 90% concentrated solution will consist of 90cm3 of hydrogen peroxide, and 10cm3 water. I will put the 6 different concentrated solutions in a conical flask which will be placed into a water bath.

Because a pipette is a very accurate way of measuring volumes, I believe that this will be Ray Ban Sale the best method to make up the concentrations. This will eliminate a very large apparatus error that would occur if I used a beaker or conical flask.

Controlled variableControlled variable the controlled variable consist of all the other factors which must be kept constant.

This will be the mass of yeast for each experiment (0.2g). I will make sure that I measure 0.2g of yeast as accurately as I can using the balance. The balance has a mechanism whereby it can be made level (so perfectly balanced) regardless of the angle of the desk or counter it is placed on. I have explained this is my method below. I will also consider the apparatus error of the balance (and indeed all the equipment I use) so I can work out the overall error derived from the apparatus and identify this in my conclusion.

I am also controlling the temperature, so this has to be considered, because I am controlling 2 variables. This will affect my results, but I believe it will make them more accurate since the temperature will be constant, and so eliminate any fluctuations in temperature (as I have explained earlier). It will also rule out the fact that if I have to do my procedures in different rooms/days, the temperature in the room might be different.

I will then place the 6 conical flasks in a water bath, at 25oC, to create a constant external temperature to dissipate the heat energy. I will do this first to ensure that the mixtures have enough time to reach a constant temperature, rather than only putting them in for a short time because this will mean there may be fluctuations in temperature of the different molecules which I was initially trying to eliminate.

Next, I will grind the yeast into a powder using a pestle and mortar. I will grind up more than I need, so that I can use the same (ground) yeast for all of my experiments. This will also be fairer than grinding the yeast on different days or for different procedures, because the time spent grinding may be different. Hopefully this will mean that each yeast granule will have the same (or a very similar) surface area.