Investigation into Effect of Surface area on Catalase activity in potato.

Aim:

In this investigation, my aim is to find out how the factor Surface area effects Catalase activity in a potato.

Introduction

Enzymes are globular shaped proteins. They act as catalysts as they help speed up reactions and remain unchanged themselves. Enzymes are composed of amino acids, arranged in chains, which are the n moulded into 3-dimensional shapes.

The molecules which the enzymes breakdown, are often referred to as substrates. The shape of the substrate is complimentary to the enzyme’s active site. The enzyme has a very specific 3D shape into which only one specificly shaped substrate can fit into it. After the substrate has taken its place in the active site, it is broken down by the enzyme into a product or products. Now, the product(s) have to leave the site as they do not have the complimentary shape anymore.

Cells have an enzyme called catalase to breakdown hydrogen peroxide, which can kill the cells, into two safe products.

2H2O2 2H2O + O2

This type of reaction where a molecule is broken down into two smaller products, is called a catabolic reaction.

In order to investigate the effect of surface area on the activity of catalase, I am going to measure the volume of oxygen gas released in order to determine the rates of reaction.

Hypothesis:

The more sections that the potato is cut into, the greater the surface area of the potato there will be. Therefore, I predict that the greater the surface area of the potato, the higher the rate of reaction will be. It is reasonable to predict that the volume of oxygen given off is proportional to the surface area available.

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If there is a greater surface area of the potato, there would be more the catalase molecules able to come into contact with the hydrogen peroxide. Enzymes work when their active sites come into contact with their complimentary substrates. Therefore, the greater the surface area, the more enzymes and the more active sites will be exposed to the hydrogen peroxide. Therefore the more Oxygen will be given off. For example, If there is a potato cylinder which is 5cm in length and 1cm in diameter(A) and then the same sized cylinder was produced again but cut in to half (B), the one that is cut (B)will have a greater surface area. Reason being that (B) has produced to extra ‘ends’. Then, if the two samples of potato, (A) and (B) was placed in hydrogen peroxide, (B) would have a higher rate of reaction since it was the one that has a greater surface area. The amount of Oxygen given off is proportional to the size of surface area. The larger the surface area, the higher the rate of reaction therefore the more Oxygen given off. If the surface is doubled, then directly the volume of oxygen given off will be doubled.

Apparatus

In order to complete the experiment, the following apparatus will be used:

Potato
Scalpel

Tile
0.1M H2O2
boiling tube
cork borer
10cm3 measuring cylinder
stop watch
10cm3
water container
gas syr inge
test tube rack
ruler
delivery tube and bung

Health and safety

Within this experiment, certain health and safety regulation need to be taken into account.

Scalpel: the scalpel must be used very carefully as it can cut you. It is best that the potato is cut on a tile for higher safety measures.
Glassware: All glassware must be handled with care. It is easy break, which can obviously cut you. Apparatus such as boiling tubes should be handled with extreme care especially when the contain contents such water.

Hydrogen Peroxide: Hydrogen Peroxide is an oxidising agent. This means that oxygen gas is given off. This can be dangerous in the way that oxygen can assist any burning fires that may start.
Safety goggles: it is necessary to wear safety goggles during the experiment, as Hydrogen peroxide can cause major eye damage if it were to get into your eyes.
Cork borer : the cork borer has a potential hazard itself. While in use, the potato being cut should be held down by your other hand. If not, the borer can slip and cut you.

Method

In order to complete to this investigation, the following method needs to be followed:

First of all, I will set my apparatus up in a suitable manner
Using the formula 2πrh +[2πr x 2πr], I will work out the surface areas of the cylinders being tested in this investigation:

1cm in length, 1cm in diameter = 4.71 cm3
2cm in length, 1cm in diameter = 7.85 cm3
3cm in length, 1cm in diameter = 10.99 cm3
4 cm in length, 1cm in diameter = 14.14 cm3
5cm in length, 1cm in diameter = 17.27 cm3

place the potato onto the tile

using the cork borer, take a sample of potato, cut this piece in cm intervals, ranging from (1-5cm)using scalpel and plastic rule.
Place 30cm3 of .01M hydrogen peroxide into the boiling tube, using the syringe
Fill the measuring cylinder and water container with water
Place the potato cylinder into the boiling tube and push in the bung into the boiling tube
As soon as the cylinder comes into contact with the hydrogen peroxide, start the stop watch and collect oxygen for the following 5 minutes.
Record the volume of oxygen collected
Discard the contents of the boiling tube
Repeat the experiment using different ranges of surface areas
When all the different ranges have been covered, repeat the whole experiment again to obtain a second set of results.

Justification of method:

I have chosen to use this method because it is safe, efficient and accurate. I feel that it will help me to obtain reliable results.

Controls/variables:

Within this investigation, there are many controls/variables that could affect the experiment.

Temperature: the higher the temperature, the higher the rate of reaction. This theory applies only up to a certain point. Heat is energy, so when particles gain more kinetic energy, they tend to move around much faster. When they move around quicker, they increase their chances of collision. Therefore, the collisions between the active sites and the substrates are more likely. This increases the rate of reaction. However, enzymes hold a very specific 3D shape, and so if the amino acids of the enzymes gain too much energy, its hydrogen and ionic bonds will break causing the distortion of the tertiary structure. This will mean that the enzyme can no longer act as a catalyst. The catalyst would have been denatured.

The optimum temperature for this reaction is around 20°C.

Ph: if pH values are too low or too high, the enzyme will become denatured. Reason being, at a low pH there will be too many H+ ions. This would disrupt the shape and hence denature the enzyme. In the same way, at a high pH, there would too little H+ ions and this will again disrupt the shape and hence denature the enzyme.

The optimum pH for this reaction is 7.

Concentration of catalase: the higher the concentration of catalase, the higher the rate of reaction as more catalase molecules are exposed to the hydrogen peroxide. The larger the number of catalase molecules, the higher the chance of collision between the active sites and substrates. Therefore, the concentration of catalase will be kept the same throughout the experiments as the higher concentrations give a higher rate of reaction.
Concentration of substrate: the higher the concentration of substrate, the higher the rate of reaction. Reason being that with a larger number of substrate molecules, the chance and frequency of the collisions between the reacting particles is increased.

I found that 30cm3 of 0.1 hydrogen peroxide provided the most manageable amount of oxygen produced

Precision & Reliability

To ensure the experiment is precise and provides reliable results:

Repeat the whole experiment 3 times in order to obtain more accurate results.
Use a gas syringe to be enable accurate measuring of oxygen. A gas syringe is used instead of a manometer, which is where O2 bubbles are counted.
If a manometer is used, it could be inaccurate as some of the bubbles may be missed and not counted. They could be miscounted.
The potato cylinders need to be cut precisely, it is necessary for their edges to be cut straight using the cork borer.

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