Unit 4 - Controlled Variable

Experiments in biology are actually very difficult to control completely. Take the study of "Does adding fertiliser make a plant grow bigger?". For a start, there are many different fertilisers so the results could differ from one to another. You would need to do many different experiments. The plants you use is a variable that needs to be controlled so you use the same type of plant in all of your tests. But genetics of each plant should also be controlled by using clones. Even if you did use cloned plants, there are other factors that should be controlled to ensure a fair test, like using the same soil. same size pot, same amount of light and temperature and some other factors too.

The conclusions that you draw from any biological experiment should show that you understand this and suggest some of the places that inaccuracy could have come into your experiment through no fault of your own. To overcome this, professional scientists repeat experiments many, many times so that they can 'average' the results. This helps to reduce any inaccuracies caused by the controlled variables.