Electron and Light Microscopes Revision Scientific Detection

Light and electron microscopes - Objectives To be able to describe the differences between images formed from light and electron microscopes To be able to describe how the sample preparation is different for the 2 microscopes

Starter – what type of microscope does the image come from?

Light microscopes These are the microscopes you are used to in school You should be able to label the important parts Objective lenses, stage, arm, focus adjuster, eyepiece

Light microscopes Samples are generally dead Very thin sample slices are needed The sample may have to be stained to show up important features eg, nucleus of cell The image is 2D

Sample preparation Put a drop of water on the specimen Examine the specimen with a light microscope If required, stain the specimen placing a drop of stain touching the edge of the coverslip Place the specimen on a microscope slide Use a mounted needle to lower a coverslip over the drop of water slowly. Avoid air bubbles Re-examine the slide under the microscope

Electron microscopes Samples are dead Samples are sometimes thinly sliced Samples are coated in chemicals or gold Samples are placed in a vacuum Photomicrographs are 3D

Sample preparation Thin slices of the sample are made The sample is coated in gold or treated with chemicals Sample is dried to remove moisture The sample is placed in the vacuum chamber of the microscope The sample is examined under the microscope The micrograph is examined and digitally coloured to enhance it

Quick Quiz Which microscope requires thin slices of samples? –Trick question, both (EM can do 3D as well) Which microscope can be used for living samples eg, water fleas? –Light Which microscope can give 3D images? –Electron What is the image from an electron microscope called? –Photomicrograph