How to approach and answer AQA A-level Biology Questions that need you to interpret Graphs- lots of AQA past paper questions

Magical top tip: DO NOT LOOK at the question first - LOOK at the data first

This simple trick can transform how easily you will be able to answer graph questions

• ALWAYS LOOK AT THE DATA FIRST

• Look closely at the graph or table

• Graphs - look very carefully at the axes - have they plotted rate or time, mass/volume or concentration ? Often students assume enzyme graphs have rate on the y axis - sometimes they don’t !

• Table - is the IV in the first column ? What are the units of the DV ? Has a mean been calculated ? Is the data in each row consistent ?

• are there range/SD bars on the graph ? remember this indicates the variation in the data that was used to calculate the mean

• do the range bars or standard deviation bars overlap ?,

• If the Standard deviations (+or- 2 SD overlap then the DIFFERENCE between the MEANS is due to chance - the differnce between the means is not statistically significant).

• In a table what range is in the replicates when you compare to the mean ?

• what trends can you observe ?

• then think about what principle of biology is being shown by the the trends, for instance - enzymes and substrate concentration or mitosis and distance from the root tip

• How would you explain the highest value, the lowest value, the point at which the line crosses the x axis, how would you explain the largest range, how would you change the method to reduce the spread in the data ?

Have a look at these 20 excellent recent graph interpretation AQA Questions

An old collection of OCR maths-heavy questions for extra practice

Y12 and Y13 AQA small group weekly class information

Key Concept: Independent and Dependent Variables

A guest blog from Dr Jenny Shipway, who studied biochemistry at university and now works in science communication and education training.

To understand experimental design and graphs in exam questions, you will need to confidently recognise the difference between different types of variables. Master this now and it will also make it easier to learn content that is taught using graphs.

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What is a Variable

A variable is any value that does/might change during an experiment.

Variables can include things like pH, temperature, colour, or the concentration of substances. The amount of time that has passed is a variable, as are rates of reaction.

• Some variables’ values are fixed deliberately by the scientist.

• Some variables’ values are changed deliberately by the scientist. These changes are planned in advance so the measured values are usually known before the experiment starts.

• Other variables’ values are allowed to change naturally as the experiment progresses. These values can be measured to provide useful data.

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Simplify Your Exam Approach

During exams it’s very easy to get overwhelmed with information. When this happens, your brain makes guesses and jumps, often without you being aware. This is why students so often mis-read graphs and/or make ‘silly’ mistakes.

Excellent Exam Tip: work out what the experiment was and how the graph is presented BEFORE looking at the exam question.

This will …

• Reduce the number of things you’re thinking about at one time

• Reduce the risk of you jumping to (incorrect) conclusions

• Help you focus on understanding the experiment

You might feel an urge to rush forward to look at the question, but trust me that won’t save time. You will not be able to answer the questions unless you understand the graph, and rushing forward will make that more difficult, not less.

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Identifying Variables

Variables described in the experiment and named on the graph axes may include:

• Independent Variable – this is the thing that is changed deliberately by the scientist in a planned way. This is the thing that we expect to cause a measurable effect. 

• Dependent Variable- this is the thing that is measured by the scientist. The value is not known until it is measured, and the value will depend upon the value of the independent variable.

• Control Variables – these variables are fixed to one unchanging value throughout. For example, all experiments might be carried out at 20°C, in which case temperature is a control variable. (Important: this is a different thing from ‘a control’).

The purpose of the experiment is to answer the question: how does the independent variable affect the dependent variable?

There are usually many factors that could be affecting the dependent variable, so it’s important to control as many variables as possile. The idea is that if only one thing has changed (ie the independent variable), then you can be more confident the affect is due to that one thing. 

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An Example 🍅🍅🍅

If you wanted to work out what temperature was best for growing tomatoes, you could try growing plants at different temperatures to see which plant produced the most fruit. Everything except temperature should be kept the same so that you’re sure that any difference in fruit yield is due to temperature.

The question is: how does temperature affect fruit yield?

You will deliberately be changing the temperature to pre-chosen values, so temperature is the independent variable.

You will need to measure the weight of tomatoes produced to find out this value. So this is the dependent variable. The weight of fruit will depend upon the temperature.

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Check your Understanding

Can you identify the independent and dependent variables in the following examples? Which variable was independently fixed by the scientist? And which was measured/recorded during the experiment?

(Ignore the positions of the data points, you only need to look at the axis labels.)

Usually, you will find the independent variable along the x-axis, and the dependent variable up the y-axis. But that’s not always the case (as you hopefully spotted in some of these examples). Do not let your brain jump to an assumption! You must always check this.

You need to be 100% confident of your variables before you move forward to look at the actual question, or everything else will get really confusing. It’s a good tip to write on the exam paper which variable is which (eg label the graph axes “I.V.” and “D.V.”)

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Multiple Independent Variables

It’s possible to have more than one independent variable.

For example, some experiments are run twice under different conditions. See this graph:

First, look at the axes. The independent variable here is the amount of time that has passed (on the x-axis): the scientist decided before the experiment at what times they would count the fruit. The dependent variable is the number of ripe fruit (on the y-axis): the number of ripe fruit is the thing the scientist is measuring, and this depends on how much time has passed when the measurement is taken. We’ve seen this before.

Now look at the data. There are two sets of data plotted on the graph. One experiment has been run with fertiliser, and one without. So the presence of fertiliser is another independent variable – it’s something else that affects the value of the dependent variable.

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Example A-level Exam Questions

Can you identify the independent and dependent variables in the following A level Biology exam questions?

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If this post has been helpful, please like ❤️ below and share with your friends. 

For more general information about graphs, see the post about how best to approach A level biology graph questions.

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Repeatable or reproducible ? Valid or accurate ? Glossary of vocabulary

A great glossary of terms that apply to  A level Biology questions and answers. Learn them and use them !

How to approach and answer A-level Biology Questions that need you to Analyse Figures, Tables and Images - lots of example past paper questions

DO NOT LOOK at the question and then look at the data to answer the question.

• ALWAYS LOOK AT THE DATA FIRST

• Look closely at the graph or table

• Graph look very carefully at the axes - have they plotted rate or time, mass/volume or concentration ? Often students assume enzyme graphs have rate on the y axis - sometimes they don’t !

• Table - is the IV in the first column ? What are the units of the DV ? Has a mean been calculated ? Is the data in each row consistent ?

• are there range/SD bars on the graph ? remember this indicates the variation in the data that was used to calculate the mean

• do the range bars or standard deviation bars overlap ?

• In a table what range is in the replicates when you compare to the mean ?

• what trends can you observe ? then think about what principle of biology is being shown by the the trends.

• How would you explain the highest value, the lowest value, the point at which the line crosses the x axis, how would you explain the largest range, how would you change the method to reduce the spread in the data ?

Once  you have a coherent understanding of the trends  - only then look at the question.

try this - about 20 questions with data and analysis

If you found it useful then please ❤️ (at the bottom of the page) and share, you can follow me on instagram - alevelbiologytutor

Tuesday night group tutoring topics and Y13 & Y12 OCR A and AQA small group weekly class information

Tips and Practice Questions for the Practical component of the Theory papers - A-level Biology

15 % of the June 2017 A-level Biology examinations will be examining practical skills. Here are some excellent practical exam questions which will challenge you to think about the nature of experimental design, independent and dependent variables. 

Statistical analysis and graph plotting are also in the questions.

Remember

• Never write "amount" you mean mass, volume or concentration. 

• Refer to "a control experiment" or "a variable that I will control (and then name the value and method of control)" but never to "a control variable"

• Independent variable is what you change.

• Dependent variable is what you actually measure in the experiment (not rate).

• Organisms vary from each other unless they are clones !

• When you suggest improvements think about improving the method rather than the equipment (e.g. control a variable that wasn't previously)

• Validity means does the experiment actually test what it set out to test

• Reliable is an outdated term - Repeatable or Repeatablity is now preferred

Here is some advice on tables and graphs. And here on measurement and language.

Here are 13 pages of practical based questions in pdf form.

Please "like" and share with your friends if you find that this helped your improve your understanding

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How to do Tables and Graphs - terrific guidance from Exam Boards for A-level Biology

Rather than being assessed seperately, practical skills are included in the theory paper. Like this OCR question from the sample paper

Please like and share (and click on a advert to help with the hosting costs !)

There is plenty of excellent guidance on how to plot graphs and draw tables in the OCR practical booklet  ..... pdf here

Precise but not accurate ? Language of Measurement - crucial for Biology Practical Exam Questions

Precision, control variables, independent variables ? Confusing for many students, however, particularly important now that this year practical skills are assessed in the exam paper. 

An extremely useful document is the Language of Measurement. Reading it is a great start to improving your approach to practical questions. Below are 3 pages.

Original PDF - is here