In TOK students learn how our brain uses previous experience to interpret images we see with our eyes. Sometimes our eyes can play tricks on us and we can see a scary shape in a shadow, or a face in the clouds. Eye witness testimonies in court are particularly unreliable as the witness has already been influenced by their previous experience, as well as any leading questions the police might have asked. These influences are referred to as "problems of perception" in TOK.

In Biology when we look at electron microscope images, or when we look at specimens under a light microscope we must be careful of influences, especially when making a new discovery. Charles Darwin was famously cautious about the use of high powered microscopes before observing specimens under low magnifications.

These are a few examples of the problems of perception in biology.

• Students often mistake an air bubble for a giant nucleus or an interesting cell structure.
• Students copy the shapes of cells from the text book rather than copying real individual cells from a slide.
• Crystals can sometimes appear in electron microscope images and look like structures which don't exist.
• The shape of cells and organelles changes depending on the way that the slice of material has been cut for the slide.