GCSE Science: How To Draw The Perfect Graph
Amy studied at the University of Bristol and is our revision blog guru. She only graduated recently so understands the pressures of being a student better than most, and is here to share her wisdom so that you revise effectively, smash your exams, succeed at school and write cracking university and job applications.
As you may have noticed when going through your GCSE past papers, graphs come up quite a bit in Biology, Chemistry and Physics exams. Collecting results from experiments and investigations and reaching conclusions is only half the battle though, as you also need to make sure your data is clear and accessible, and presented in the right way.
You’ll have encountered many types of graph in your studies so far, and whether they’re line graphs or scatter graphs, there are some rules that apply across the board. In order to draw, label and describe them correctly to get full marks, follow these top tips…
1. Label your axes clearly
This is one of the most important parts of the graph-drawing process. Your ‘x’ axis must show your independent variable (the thing being changed for each measurement) while the ‘y’ axis is for the dependent variable (the thing being measured each time). Each of your axes should be clearly labelled to show what they’re measuring, with the units of measurement noted alongside them.
Unclearly or incorrectly labelled axes could count against your graph before you’ve even entered your data, so it’s vital to get those foundations correctly in place.
TOP TIP: To refresh your memory on independent and dependent variables and what they mean, head to this blog post.
2. Choose a suitable scale for your axes
When marking out the numbers on your axes, keep things simple. Choose a suitable metric and scale, taking into account:
- The relevant unit of measurement – What are you measuring ? Volume in litres or millilitres, speed in velocity, heart rate in beats per minute? Whatever your unit is, always write it in shorthand on the axis so the examiner knows what you’re measuring (e.g. mm, bpm, cm, etc)
- The spread of your results – What scale do you need to use to allow you to accurately plot your results, and fit them all neatly on your graph?
When it comes to selecting a scale, we’d recommend moving upwards in easy multiples of 1, 2, 5, 10, 20, 50, or 100, depending on what you’re measuring and the results you’ve got in front of you. These multiples are make for clear scales, and are easy to read and to plot.
You should also ensure you leave an equal space between each number in the scale, that aligns with the spaces on your graph paper. Jot your numbers down with logical spaces in between, keeping your scale clear, even, and accurate.
3. DO draw a line or curve of best fit on a scatter graph
A line of best fit is the best way of showing the patterns and trends in your data, helping you reach a strong final conclusion from your investigation. Your line of best fit doesn’t have to be perfect, but should move from the first set of measurements to the last, following the trend shown by the points plotted on your graph.
You can then use this line to make predictions and approximate readings from your data, using the trend you’ve spotted.
Don’t forget that when drawing a straight line of best fit, always use a pencil and ruler!
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4. DON’T connect points dot-to-dot on a scatter graph
If you’re plotting data in a scatter graph, resist the temptation to connect the points like a dot-to-dot as you would in a line graph (see below).
However if you’re drawing a line graph (as you will often have to do in GCSE Biology to show trends over time) you can connect the dots. Line graphs are only used when both variables are quantitative.
5. Don’t ignore ‘anomalies’ that don’t fit the pattern
If you have a result that doesn’t quite fit with the rest of them, it’s understandably tempting to write it off and pretend it didn’t happen, but you don’t have to! As said above, the data is there to show you trends and patterns, and the nature of an experiment is that things won’t always go the way you expect. Anomalies are common in any experiment and are actually to be expected. Often they’re something you can work with.
If you have an anomaly on your graph, circle it and note that it doesn’t fit the rest of the data. This will show the examiner that you’ve recorded your data accurately, and that you understand how experiments work and how to treat anomalies.
Some investigations, for example osmosis-based ones in GCSE Biology, go even further and demand error bars. Error bars are necessary when you’ve performed a number of readings at each phase of the experiment and need to show the range of results you’ve picked up. The point you mark on the graph will be the mean average of those readings, and the error bars will show the lowest and highest readings you’ve recorded (as in the diagram below).
Again, if you have a result or two in the mix that mean an error bar is taking up more of the page than you’d it to, leave it in there! You won’t lose any marks for recording your findings accurately.
We hope you’ve found this helpful! For more on GCSE Science experiments, check out this blog post.