Microscopy of a banana smear: using a stain to provide contrast

Bananas (Musa sp.), and how they visually change as they ripen, will be familiar to a great many students. This activity teaches students about the use of stains to provide contrast whilst getting them to explore the differences between unripe and ripe bananas at a cellular level.

This resource uses banana smears to teach students about the role stains play in providing contrast when using a compound light microscope. The simple preparation allows students to spend more time viewing the specimen and exploring the difference between ripe and unripe bananas. Using iodine solution to stain starch grains is a robust staining procedure that produces good results every time. The application of the stain at the edge of the coverslip provides students with the opportunity to see cells at a whole range of different staining intensities. They can even see cells going through the process of being stained and the contrast developing over time.