The burette meaning - Sample Essay

The aim of my investigation is to study the reaction of Catalase and Hydrogen Peroxide. I am specifically focusing on the substrate concentration and its effect on Oxygen production. Variables There are many variables that can affect the experiment, substrate concentration is one of these, it affects the amount of oxygen produced and the time taken for the enzymes to reach their operation ceiling. The enzyme we are using is Hydrogen Peroxide the more you use the higher the rate of reaction and the more oxygen is produced.

It would come to a point where the reaction couldn’t get any faster because the enzyme would be saturated and wouldn’t be able to handle anymore, all the site would be in use. Another variable is surface area this also affects the rate of reaction and the amount of oxygen is produced. The higher the surface area, the higher the rate of reaction. Also more oxygen is produced. The higher the surface area the larger the surface the substrate can act on. Temperature has a big affect on the speed of the reaction. It would speed up the reaction to an optimum temperature where the maximum rate is achieved.

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This relationship would carry on until the temperature was raised above the optimum then the enzymes would start to denature causing the rate to drop. The amount of potato used would also affect the speed of the reaction. The more potato used the larger amount of enzyme the substrate has to work away at. This especially slows down the reaction if the surface area is kept constant. Pressure affects the reaction but not in a very significant way. pH is an additional affecter which also affects the reaction, most enzymes work best in a neutral pH (pH 7) this is when the enzyme is at its optimum activity.

If the pH goes over or under this the reaction will be affected, probably slow down. When pH does go up or down it makes the enzyme inactive. This means it can be reactivated if the pH rises or falls again. However, if the pH rises or falls to the extremes the enzyme may be denatured, meaning it cannot be resurrected. Input and Output Variables In my experiment I am going to investigate the affect changing the concentration of substrate has on the rate of reaction and amount of oxygen produced. This means I will be using Hydrogen Peroxide and a standard amount of potato.

To measure the activity of catalase I am measuring the amount of Oxygen produced, I will be measuring it in ml. This will show how much of the catalase is reacting with the substrate. Prediction I predict that the higher the substrate concentration the higher the amount of Oxygen produced in the time given or the higher the rate of reaction. I predict that this relationship will go on until the rate of reaction completely plateaus. I believe this will happen because the substrate concentration will eventually reach a point where the rate of reaction will change very little or not at all.

The maximum rate is never actually reached but as mentioned above it will reach a point where it will appear not to change at all. The reason this occurs is that all the active sites at that moment in time are saturated with substrate. This means that the excess substrate that is left over has to wait its turn to complex with the enzyme. Therefore at high substrate levels both enzyme concentration and the time it takes for dissociation of the enzyme/substrate molecule limit the rate of the reaction. This called the collision theory. Preliminary Work

In our investigation we had to find out the value of the constants that we were going to use in our experiment. This included doing a series of investigations to see which were the correct values and what would produce the most reliable results. The things we were investigating were: How much substrate (Hydrogen Peroxide)(H2O2) and how much water were we going to use?  What was the best number of pieces of potato to use?  How long were we going to time the experiment for?  What size were the pieces of potato we were going to use?  How big would the surface area be?  What would the temperature be?

We had to solve some problems, for example, the Hydrogen peroxide wasn’t covering all of the potato so we had to make the amount of potato smaller. We had to do this because we couldn’t change the amount of substrate concentration because it all had to fit into a syringe and it was already completely full. This would also create a faster reaction because there is not so much potato that the substrate has to react with. Another problem we had to solve was that when you inject the Hydrogen Peroxide it would always push alot of bubbles out which went into the burette meaning we got completely wrong results.

The solution to this was incredibly simple, all you had to do was wait for the bubbles to be expelled and then you could put the burette on the evacuation tube. Accuracy and Values We have a lot of values that we are keeping constant here they are:  We had six values for Hydrogen Peroxide, Substrate concentration (ml) Water concentration (ml)  We measured this using a syringe it was accurate to the nearest 0. 1ml. We are going to repeat this 3 times so we can get an average and therefore a more accurate picture of the rate of reaction.

The amount of time we are giving the experiment is 3 minutes. We believe this will give the experiment enough time to show good reliable results that conform to the predicted pattern. We are using a stop clock that has an accuracy of 100th of a second.  We are going to keep the temperature as constant as possible, but we are really at the mercy of the schools central heating system. We estimate that it will be around 20i?? c. we didn’t actually use anything to measure the temperature this could be one problem we have in our method.

The size of our potato was 1cmi??, we believed this would be a good size because it would react reasonably well and wouldn’t take to long to start reacting. We used a rule to measure this it was accurate to 0. 1cm.  We use 4 equally sized pieces of potato all of them were 1cmi?? so the total surface area was 4cmi??. We used the same rule so the accuracy was the same. Equipment We are using many different pieces of scientific equipment. Here is a list:  A syringe.  A boiling tube with a bung in to stop oxygen escaping and tube linking to the burette, which measured amount of oxygen produced.

A beaker to hold the water.  We also needed some distilled water to dilute the acid. We used a stop clock to time the experiment. Method To do the experiment effectively you have to follow a very strict set procedure so that you don’t mess the experiment up. You have to make sure everything is exactly the same at the start of each separate process so the investigation is fair and not bias in any way, which would produce bad results. The first thing we had to do was make sure we had sufficient amount of all the equipment we needed.



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