Biology catalyst couursework

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MATTHEW HUMPHREY 10D

Biology Coursework

Plan

Enzymes are biological catalysts. They speed up chemical reactions in all living things. Each particular enzyme has a unique, 3-dimensional shape shared by all its molecules. Within this shape there is an area called the active site where the chemical reactions occur. Probably the fastest enzyme known is called catalase it breaks the chemical hydrogen peroxide down to water and oxygen.

The equation for this reaction is: 2 H2O2  2 H2O + O2

There are a few factors that affect the rate of an enzyme reaction such as:

  • pH- Enzymes are proteins; they have a structure that is sensitive to pH. In very acidic are alkaline conditions the shape can change. This means the active site will no longer fir the substrate and a reaction will not occur.
  • Temperature- Molecules move faster at higher temperatures causing more collisions which will cause the reaction to happen quicker. Temperatures above 40ºC can denature an enzyme thus changing the shape of the active site.
  • Surface area- A larger surface area means that more of the enzyme is in contact with the substrate. This will therefore insure an increased reaction rate.
  • Concentration- A more concentrated solution has more molecules in a certain volume. Therefore more collisions will occur between the enzyme and the substrate resulting in an increased rate of reaction.

Method

For my first preliminary investigation I decided to choose which catalyse would be best suited to the job. I had a choice of mashed potato, peas, raw liver and yeast, I measured out an equal amount of each (1g) as this would make it a fair test and would enable me to see which was the easiest to measure. I timed ten seconds on a stop watch to see which reacted fastest and held a glowing splint over the solution to see which produced the most oxygen. My results showed me that peas and mashed potatoes reacted little and that yeast reacted next best with raw liver reacting the highest. However, I had to think about which product would be the easiest to handle in the final investigation and I decided that raw liver was very hard to measure to the exact gram and was hard to work out an even surface area every time. Consequently I decided to use the yeast as it is the easiest to measure and still has a good rate of reaction with an even surface area. I also learnt from this first preliminary investigation that using a gas syringe next time would give us a more accurate reading and leave less room for mistakes to be made.

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The variable that I am going to use is concentration as this is the most practical out of the four variables. The collision theory explains how concentration affects the rate of reaction and therefore the amount of oxygen produced:

For a reaction to occur the reactant particles must collide. Only a certain fraction of the total collisions cause chemical change; these are called successful collisions. The successful collisions have sufficient energy (activation energy) at the moment of impact to break the existing bonds and form new bonds, resulting in the products of the reaction. Increasing the concentration of ...

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