Analysing, Drawing Conclusions and Evaluating - Interpretation of Results - As the enzyme concentration increases so too does the volume of juice.

AS Level Biology Coursework G & H

Analysing, Drawing Conclusions and Evaluating

Interpretation of Results

As the enzyme concentration increases so too does the volume of juice. This is because as the concentration of enzyme molecules increase there is more chance of a collision with an apple substrate molecule. If the chance of a collision is increased then the number of collisions will increase resulting in a higher rate of reaction.

The enzyme combines with the substrate to form an enzyme-substrate complex.

Enzyme + Substrate ¬¬¬> Enzyme-Substrate Complex

The enzyme-substrate complex then breaks down to give the product and releases the enzyme in an unchanged form:

Enzyme-Substrate Complex ¬¬¬> Product + Enzyme

So I can conclude that the rate of reaction is directly proportional to the concentration of the enzyme. This is clear from the results that I myself obtained and from the class average. We can see that as the concentration of the enzyme increases so does the volume of juice (product) produced from the apple. This is because the more enzymes that are present the greater the number of active sites available for the substrate to fit into under the lock-and-key hypothesis, thus forming a greater number of enzyme-substrate complexes and thus forming a higher product rate (apple juice).

Enzyme concentration is directly proportional to the rate of reaction provided the substrate concentration is maintained at a high level and the pH and temperature are kept constant. We know that the substrate concentration is maintained at the same level in all samples, this done by ensuring that all samples are of equal mass and we know that all the samples were placed in an incubator at 40°C thus ensuring that the temperature effects the rate of reaction in all samples in the same way.

Graph: - From 0% ¬> 0.25% concentration we can see the greatest rate of reaction ...

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Graph: - From 0% ¬> 0.25% concentration we can see the greatest rate of reaction as there is an abundance of substrate molecules available to combine with the active site of the enzymes producing a large gradient on the graph.

As concentration increases from 0.25% ¬> 0.5 the gradient decreases slightly as the number of substrates available to react decreases as they have been used up but still there is yet more of an increase in the rate of reaction and formation of product as there are yet more enzymes present therefore a greater number of active sites available to combine with the substrate and therefore a greater yield of product produced.

From 0.25% ¬> 1.0% there is a steady increase in the gradient where 1.0% has the greatest value, which proves that an increase in the concentration combined the constant pH and temperature and a high level of substrate molecules produces a greater rate of reaction than if there was a lesser concentration of the enzyme.

Evaluation of Practical Work

Despite the controlled conditions that the experiment was conducted under, there were still obviously a number of errors in the method as a number of anomalies are evident.

These anomalies could come from a number of sources in the method, the first being step 1. When finely chopping the apples and crushing them I noticed that this process was producing a small volume of juice. Although the volume was small it will still be counted as product and is enough to effect the end result and could help to explain a number of anomalies present in the results. In fact it is this reason that I feel explains why group 4’s (my own personal group) 3rd result (0.5% enzyme concentration) is higher than that of their 4th result (0.75% concentration). This could be easily avoided if a step was included that involved the draining the mass of apple of its juice after the chopping and crushing process.

I also noticed that some apple was crushed more than others during the chopping and crushing process, this decrease in surface area will have an adverse effect on the results. The pectinase will not be able to act on all parts of the apple as it would be able to if the apple was completely crushed to a fine pulp. It is this reason that I believe is the main cause of the anomalies in the results. If we had access to a homogeniser then this could have been prevented. This source of error could help to explain group 2’s anomalous results, the only great change in the volume of their product produced is between 0% enzyme concentration and 0.25% enzyme concentration; the rest of their results are relatively concordant with each other.

In step 6 we were told to place the enzyme solutions in each beaker appropriately, this means that the first beaker containing apple will have been exposed to the enzyme for a longer period of time than the last beaker giving the enzyme more time to act on the apple and more time to produce more product leading to the possibility of an anomalous result. If the enzyme was placed in each beaker in a staggered fashion and a timer was set for each separate beaker then this source of error would no longer be fundamental to the results. This source of error could explain why group 6’s middle three results (i.e. 0.25%, 0.5% & 0.75%) are relatively concordant with each other.

The thirty minute incubation period commenced from the moment that the first group placed their beakers in the incubator, this means that they had more time exposed to the heat of the incubator and the enzyme than the other groups. This source could be easily rectified if a timer was started for each individual group from the moment whence they place their experiments into the incubator.

James Hobson 26/04/07

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