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What Biologists Do


At school, biology is often taught as a collection of facts that you need to memorise for exams. Sometimes its easy to forget that every fact ever written on a whiteboard or in a textbook was originally discovered by a biologist in a lab.


Biology is an experimental science, this means that facts are found by running an experiment and observing the results.

Bench = lab bench (desk), not a park bench

Control = one bit of your experiment that is your 'baseline' or 'reference' that you need for comparison

Back in the 1800s, people used to believe that life could appear out of non-living things, like fleas appeared out of dust. In 1859, the famous french biologist Louis Pasteur (1822-1895) ran an experiment to test if this was true.

Louis used bottles filled with broth, which, if he left on the bench for a few hours, became cloudy as they filled with bacteria and microbes (think of gone-off soup). To see whether these microbes appeared spontaneously or, as Louis suspected, fell into the broth whilst floating about in the air, he made some special bottles. These bottles had 'swan necks', a twisted neck which meant that anything in the air would fall into the neck of the bottle, but never come in contact with the broth itself. For his 'control broth', he snapped off the swan neck. When he treated his swan neck and non-swan neck bottles exactly the same (same broth put in at the same time in the same room), he saw some interesting results: his 'control broth' went cloudy, but his swan-neck broth was completely clear!


Before Louis, people didn't realise disease came from spreading germs - so they weren't very bothered about hygiene or drinking clean water!


Swan neck bottle

Control bottle

Hypothesis = a theory that you can test by running an experiment

Fun fact: Louis also invented a way to stop milk going off and named it after himself - pasteurisation

Louis' experiment changed how people thought about biology and life, leading to the very important 'cell theory' i.e. all cells come from cells (look back at 'Making New Cells' in THE CORE if you want to see a video of the theory in action!).

Looking at it from another perspective, we can see Louis' experiment as an example of how all experiments are run today:

  • He had a theory or 'hypothesis':  Louis thought life did not appear spontaneously, but microbes dropped into the bottles when floating around in the air

  • He tested his theory by changing one important thing: he made the swan-neck bottles so that microbes could not fall into the broth. He also made a 'control' bottle with the neck snapped off at the same time, so he had two results to compare

  • He kept everything else that might affect his results: the type of broth, the location of the bottles and the time the bottles stood on the bench might all have affected how cloudy they became. By keeping these things the same between the 2 bottles, he made sure the results were only because of swan-neck vs no swan-neck

If you have all these ingredients: a hypothesis, a method to test your hypothesis and controls to keep everything else the same, you can make the perfect experiment.


Louis' experiment only had one result: cloudy or clear broth. Nowadays, new technologies mean we can get lots of information from a single experiment. This chapter includes pages describing some of the types of experiments we run, how they work and what we can learn from them.

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