Science 07/11/2018

# Practicals: key vocabulary

By KEVIN QUINN

Roughly 15% of the marks in your GCSE science papers will be based on the practical work which you carry out in Year 10 and Year 11. In this blog, we focus on the key vocabulary which is used when carrying out a practical investigation.

## Variables

A variable is something that can change in a practical investigation.

• The independent variable is the one which we (the experimenters) change.
• The dependent variable is the one which changes because we change the independent variable.
• A control variable is a variable which is deliberately kept the same.

For a practical investigation to be a fair test which produces valid results, just two variables should change – the independent variable (the one which we change) and the dependent variable (the one which changes because we change the independent variable). Everything else should remain the same. In other words, every other variable should be controlled. For this reason, a fair test can also be called a controlled scientific investigation.

## Example

Let’s say you wanted to investigate how eating different types of food affects a person’s maximum blood sugar level. Read that sentence again. We’re investigating how changing one variable (the type of food eaten) which we call the independent variable, affects another variable (the person’s maximum blood sugar level) which we call the dependent variable.

Every other variable would have to be controlled for the results of this practical investigation to be valid. These control variables could include:

• the mass of food they had eaten
• the surface area of the food they had eaten
• what the person had eaten earlier that day
• their initial blood sugar level
• whether or not they had done exercise

If the person had eaten one type of food while running a marathon one day, and another while watching TV the following day, we would have no idea whether a change in their blood sugar level was due to the type of food they had eaten or due to the different levels of physical activity on both days. Without controlling the other variables, an investigation would not be a fair test and so would not produce valid results.

When you’re watching videos about practicals on My GSCE Science, can you identify the independent, dependent and control variables? Questions on variables often come up in the GCSE exams!

## How science develops

We carry out scientific investigations to develop our understanding of the world around us.

A hypothesis is a statement which can be tested scientifically, for example: the amount of carbon dioxide absorbed by a plant is proportional to the light intensity.

A prediction is a statement of what we expect to happen when a hypothesis is tested, for example: if the light intensity is doubled, the amount of carbon dioxide absorbed by the plant will double.

An investigation is said to be repeatable if similar results are obtained when it is repeated under the same conditions by the same person (or by the same group scientists). An investigation is reproducible if it is repeated by a different person (or group of people) and similar results are obtained.

Science develops due to a process called peer review. This is when different scientists check each other’s work. If the results of a given investigation are reproduced by enough scientists, the hypothesis on which the investigation will be built into scientific theory.

A theory is a scientific idea which is supported by the results of scientific investigations. That doesn’t always mean that theories are correct however, they are just our best guess at a given point in time at explaining how something works!

Kevin Quinn