A level Biology exam revision resources written by A level Examiners


Light is passed through a condenser, which focuses it onto the specimen. The light travels through the specimen. The light rays are then focused with lenses, and the image either viewed directly by the human eye, or photographed.

As the light travels through the specimen only coloured material can be seen. However most biological material is transparent so needs staining to increase the contrast between different structures. Different stains are used for different types of tissues. Methyl blue can be used for animal tissues, while iodine solution can be used for plant tissues.

The key advantage that light microscopes have over electron microscopes is that living tissue can be viewed through them.

Light Microscopy

This is a photograph taken with a light microscope (micrograph) of a water flea, and shows how images of living specimens can be obtained.

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