Interpreting data

Describing graphs

If there is a 2-mark question asking you to describe the shape of a graph, the mark breakdown is usually as follows:

1 mark for stating the general shape of the graph (e.g. rises then falls)
One mark for stating at what point the graph peaks/levels off/basically a significant piece of data from the graph. This can be read off either the x- or the y-axis. For example, if temperature (degrees Celsius) were plotted against rate (arbitrary units) for an enzyme-catalysed reaction, you could say "Peaks at 38 degrees Celsius" or "peaks at 6.3 units" and either of these would be sufficient for the mark.

Practise as much as you can with these questions.

Explaining graphs

For these you need to give biological reasons why the shape of the graph is the way it is. In the above example you would say that below 38 degrees C, as temperature increases, kinetic energy of molecules increases, so more enzyme-substrate complexes are formed; 38 degrees C is the optimum temperature; above 38 degrees C, the forces holding the enzyme's tertiary structure together (hydrogen bonds, ionic bonds etc.) are overcome; enzyme denatures; enzyme-substrate complexes no longer formed. (That's far more than you'd need to say to gain all the available marks, but that's the idea.)

Standard deviation

This could either be given in a table or as error bars on a bar chart. If one of the resources A, B or C includes standard deviation in the data there is bound to be a question where you will get credit for mentioning it. (The examiner's report on one of the ISAs even says so.)

If the standard deviations/error bars overlap this suggests that the results are not statistically significant. It could be that a > b (where a and b represent mean values of some variable) but if (a-SD)
The larger the standard deviation, the more spread out the data.

	Created by Stephen Cole about 10 years ago

A-Level Biology Note on ISA: How Science Works, created by Stephen Cole on 04/04/2014.

ISA: How Science Works