Objectives: To state the resolution and magnification that can be achieved by a light microscope. Explain the difference between magnification and resolution. Explain the need for staining samples in light microscopy. Light microscope Lesson 1

In the 1860s Robert Hooke developed a microscope and used it to view slices of cork. He saw that the cork was made up of tiny chambers – they resembled the rooms that monks lived in so he named them ‘cells’. The Cell Theory (1840s) was developed by Schleiden and Schwann: –All living things consist of cells –New cells are formed by the division of pre-existing cells –The cell contains information that acts as instructions for growth. This information can be passed to new cells.

Light microscope showing lenses and light paths

Magnification is how many times larger an image is than the actual object itself. Resolution is the degree to which it is possible to distinguish between two objects that are very close together. The higher the resolution, the greater the detail you can see. Light microscope

To calculate the magnification: Total magnification = Eyepiece lens magnification x Objective lens magnification Eyepiece lens is x 10 Objective lens can be x4, x10, x40, x100 What would be the total magnification if you were using: – the x 40 objective lens? –the x 10 objective lens?

Preparing a slide Specimens are prepared for viewing by staining and sectioning. Staining – coloured stains are chemicals that bind to chemicals on or in the specimen so that it can be seen under a light microscope. Stains bind to specific structures. Sectioning – specimens are embedded in wax which can then be sliced very thinly without distorting the structure of the specimen. Useful for soft tissue (brain).

Plenary quiz 1.What is the magnification of the eyepiece lens? 2.How do you calculate the total magnification? 3.Where is the specimen placed on the microscope? 4.What is different about the x 100 objective lens? 5.What 2 things are done to prepare a specimen for viewing? 6.What is the maximum magnification of a light microscope? 7.What is the minimum magnification of a light microscope? 8.Name one structure found in plant cells but not in animal cells. 9.Name one structure found in animal and plant cells.