Practical Skills in Biology

Practical skills in biology

A quarter of your biology marks come not from facts, but from working like a scientist. In Unit 3 you carry out a set of prescribed practicals and then sit a written paper about practical work. The hands-on part cannot be practised here, but the thinking behind it can, and that is what this module builds. You will learn how to plan a fair investigation, name the variables you change, measure and keep the same, record results clearly in a table, spot an anomaly, take a mean to make your data more reliable, draw a sensible conclusion, and suggest how to improve the method. Get these skills right and you can tackle any practical question, whatever the biology it is dressed in.

Words for practical work

Learn these terms before the variables are matched up. They name the ideas used in working scientifically.

Match each variable to what it is

Accuracy against reliability

Two words examiners use precisely, and that are often confused. A strong answer keeps them apart.

Which variable is this?

A student changes the light intensity a plant gets and measures how much oxygen it makes. What is the amount of oxygen made?

• The dependent variable, because it is what is measured
• The independent variable
• A control variable
• An anomaly

Make your results trustworthy

Good data does not happen by luck; you build trust into it. Take several readings and repeat the whole experiment, so a one-off slip does not fool you. Use apparatus that measures finely enough for the job, and read it at eye level to avoid errors. Watch for a result that clearly does not fit the pattern, an anomaly, and set it aside rather than letting it drag your average around. Keep everything except the one thing you are testing exactly the same each time, so any change you see really is caused by what you changed. Trustworthy results are the foundation of a fair conclusion.

Pick what makes results reliable

Select everything that makes a set of results more reliable.

• Repeating the experiment
• Taking a mean of the readings
• Keeping the control variables the same
• Guessing any missing results
• Measuring only once, quickly

Order how to plan an investigation

Put the steps of planning a fair investigation into a sensible order.

• Decide the question to investigate
• Choose what to change, measure and keep the same
• Write a clear, repeatable method
• Collect and record the results in a table
• Draw a conclusion and evaluate it

Complete the practical facts

The one thing you deliberately change in an experiment is the _____ variable. The thing you measure as a result is the _____ variable. A factor you keep the same so the test is fair is a _____ variable. Repeating readings and taking the _____ makes your results more reliable.

Tap the two control variables

A student tests how temperature affects an enzyme. Tap the TWO factors that should be kept the same as control variables.

• the pH of the solution
• the volume of solution used
• the temperature being tested
• the rate of reaction measured

A fair race

A fair experiment is like a fair race. If one runner starts closer to the line, wears lighter shoes, or sets off early, the result tells you nothing about who is truly fastest. To learn anything, you make everything the same for every runner except the one thing you are testing. Change only that, hold the rest steady, and the finish line gives an honest answer. An experiment works in exactly the same way: alter a single factor, keep all the others fixed, and measure what happens. Break that rule and, like a rigged race, your result proves nothing at all.

Work out the mean

In an experiment the same length was measured three times: forty, forty-two and forty-four millimetres. What is the mean in millimetres? Give the number only.

Design the investigation

Read each situation and choose the best answer.

• You want a fair test of how fertiliser affects plant growth. What must you keep the same?
• One result is far higher than all the others. What should you do?
• You want more reliable data. What helps most?

Build a method point

Choose the word for each gap to complete one point about a fair test.

Explain how to plan an experiment

A friend must plan a biology experiment and asks how to make it a good one. Using what you have learned, explain how to plan a fair, reliable investigation.

• Explain the three kinds of variable
• Explain what makes a test fair
• Explain how to make results reliable
• Explain what to do with an anomaly
• Explain why a clear method matters