S204: Experimental Week

Biology has a high amount of practical work to prove mechanisms and pathways, so there is an experimental strand to the S204 course. We are about to start on the first week of this, with investigative week one.

The task, should we decide to accept it - and the fact it will be examine in the mandatory TMA-2 is a good indication that one should, is to look in detail at the breakdown on hydrogen peroxide into water and oxygen. There is a enzyme catalyst for this reaction found in many living cells, as it is part of the chain that disposes of oxygen free radicals. In this case, we're going to get them from a simple source, the humble potato. The experiment also involves buying some H₂O₂ which causes some interest. This is one of the alleged substances that the terrorists were planning to use in their liquid bombs, so a raised eyebrow is not uncommon when asking for some at a chemists.

We have been sent an experimental kit, which consists mostly of test tubes with rubber bungs and glass pipes in them. Also supplied are pipettes and safety glasses. I elected to wear the glasses in the first part of the experiment as I'm sure it made me look more like a proper scientist.

The potato has to be liquidised to get at the enzyme, and then left to separate into a rather unappealing mess. Also the hydrogen peroxide, various containers of water and a stopwatch are required, as is a notebook to record all the results.

Experiment one is to try and find a mixture of this potato juice, water and hydrogen peroxide that reacts at a reasonable rate. Not so fast that it sprays all over the kitchen, and not so slow that it drips at an uncountable rate. It takes a bit of practice to assemble the components in a timely manner so that drips can be counted, that give an indication how fast the breakdown is occurring.

Experiment 2 is to repeat the experiment a number of times with the chosen mixture, and see at what time the peak production occurs.

Experiment 3 looks at varying the concentration, under the hypothesis that concentration does affect the rate of breakdown.

It is deadly boring counting the drips towards the end, especially on the control samples where nothing much happens. By the end of the set of experiments I'm a little less enamoured of potatoes and their extracts than I am at the start, but I have gathered some results at least, which will come in useful.

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