- Firstly think of all the relevant variables you can change.
- Secondly think of all the variables you can measure or observe.
Different types of variables are given special names. Below is a list of some important
variable types:
- Thedependent variableis the thing that you want to measure or investigate.
- Theindependent variableis a factor (or factors) that changes which will have an effect
on the dependent variable. - In every experiment you need to know which independent variable you are testing,
and keep all the other possible variables constant. We call the the variables we keep
constantfixed variables, orcontrolled variables
Example: In this investigation, variables might include: the amount of sunshine, the types
of soil in which the tomatoes are growing, the water available to each of the plants, etc. To
which variable type does each factor belong?
- Dependent variableis the one you measure to get the results, e.g. the mass of tomatoes
- Independent variableis the ONE thing you vary to see how it affects the dependent
variable, e.g. how much light the tomatoes are exposed to (dark / dim light or shade /
bright light) - Fixed/ Controlled variablesare kept the same in all trials under investigation, because
they may interfere with the results. All tomato plants will:- Be the same species of tomato
- Get the same fertiliser (type and amount)
- Grow in the same type of soil
- Grow in the same type of container
- Get the same amount of water
- Can you think of more?
- Hypothesis
Write down astatementorpredictionas to what you think will be the outcome or result of
your investigation. This is your hypothesis. The hypothesis should:
- be specific
- relate directly to the question you are asking
- be expressed as a statement that includes the variables involved (the ‘cause’ and ‘ef-
fect’) - be testable
- not expressed as a question but rather as a prediction
- be written in the future tense
Example: During your background research you would have learnt that tomatoes need sun-
shine to make food through photosynthesis. You may predict that plants that get more sun
will make more food and grow bigger. In this case your hypothesis would be: I think that the
more sunlight a tomato plant receives, the larger the tomatoes will grow’.
Chapter 1. Introduction to Life Sciences 9