The aim of this investigation is to find out what effect pH has on the enzyme Catalase in it breaking down Hydrogen peroxide into Oxygen and Water.

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The effect of pH on the activity of Catalase

Aim:

The aim of this investigation is to find out what effect pH has on the enzyme Catalase in it breaking down Hydrogen peroxide into Oxygen and Water.  

Planning:

Before going any further, we need to find out several things such as, what provides a good source of the enzyme Catalase, things about enzymes in general as in what they are, what they do, what things effect enzymes, the structure of enzymes etc.

The enzyme Catalase is found in the human body as well as potatoes, apples, liver and several other things.

So what are enzymes?

Enzymes are biological catalysts. They speed up chemical reactions in all living things, and allow them to occur more efficiently. Although they work powerfully, enzymes are chemical molecules, made up of proteins. Each particular enzyme has its own unique, three-dimensional shape shared by all of the same type of molecules. Within this shape is an area which is the active site where the chemical reactions take place. There are two main types of enzymes:

  • Intracellular enzymes- which control reactions that happen inside cells
  • Extracelular enzymes-which control the chemical reactions that occur outside cells, for example. Digestive enzymes work outside cells in the gut.

Enzymes help to turn the substrate into the product. The active site in the enzyme helps it to recognise its substrate in a very specific way. Just like a key only fits into a specific lock, each enzyme has its own specific substrate. This is called the lock and key theory.

Factors:

There are several factors which affect the way an enzyme such as Catalase works. Every enzyme has optimum conditions they work best in because enzymes are very sensitive.

Enzymes work best when they have high enough substrate concentration for the reaction they catalyse. If too little substrate is available the rate of reaction is slowed and cannot increase any further. If too much product accumulates, the reaction can also be slowed down. So it is important that the product is removed.

The pH must be correct for each enzyme. If the conditions are too alkaline or acidic then the activity of the enzyme is affected. This happens because the enzyme’s shape, especially the active site, is changed. It is denatured, and cannot hold the substrate molecule.

Temperature is a key factor too. If it is too cold the enzymes will move around slowly to meet the substrate molecules, so the reaction rate is slow. Likewise, if it is too warm they do not work properly either. This is because the extra heat energy shakes them around so much that the active sites change shape so, just like with pH, the enzyme molecules are denatured, and can’t hold the substrate.

Pre-test: 

To be able to carry out the experiment successfully, I have to do a pre-test to determine the best way to carry out the experiment. I will be testing for which pressure to time, 5KPa or 10KPa. The method for my pre-test is below.

Apparatus:                                                         

  • Bung
  • Conical Flask
  • Delivery tube
  • Pressure Sensor
  • Stop-watch
  • Petri dish
  • Digital balance
  • 2 Measuring cylinders
  • pH solution 4.4, 5.2, 6.5, 7.5 and 8.5
  • Hydrogen peroxide (H2O2)
  • Grated Potato
  • Syringe
  • Paper
  • Pen
  • Spoon
  • Grater
  • Distilled water

Method:

  • Gather the apparatus e.g. H2O2, pH 4.4 solution, and potato etc
  • Grate the potato
  • Measure 3g of potato by putting the Petri dish on to the digital balance and setting it on 0g and then put the potato on the Petri dish until the scale reads 3g
  • Measure 20cm³ of H2O2 in a measuring cylinder making sure you read from the lower meniscus
  • Measure 10cm³ of pH 4.4 solution in a measuring cylinder making sure you read it from the lower meniscus
  • Put the pH 4.4 solution and H2O2 in the conical flask
  • Attach the syringe to one of the outlets of the bung
  • Attach the delivery tube in the other outlet
  • Set the stop-watch on count-up
  • Put the grated potatoes into the conical flask with a spoon and immediately close the flask with the bung and while doing this attach the other end of the delivery tube to the pressure sensor
  • As soon as you’ve put the tube in the pressure sensor start the clock
  • Hold the syringe while doing the experiment
  • Measure the time it takes for the pressure to reach 5KPa and record the time on a table
  • Repeat this experiment once for each of the following pH 5.2, 6.5, 7.5 and 8.4
  • Before reusing the equipment for the next pH use distilled water to wash the conical flask and the measuring cylinders
  • Do the same experiment again but this time measuring the time it takes for the pressure to reach 10KPa
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Here are the results for the pre-test:                                

 As you can see both experiments gave me reasonable results because in pH 4.4 and 8.4 the least pressure is produced but pH’s 6.5 & 7.5produce the most pressure which is correct according to my research. I decided to choose 5KPa because it will take less time to do the actual experiment, hence saving time. The other conditions such as the amount of potato and the volumes ...

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**** This is a fairly thorough account of a catalase investigation including detailed and correct explanations. Descriptions of variables involved could have been better.