2.2.1 Microscopy

1. All living things consist of cells

2. Cells are the basic unit of life

3. New cells are formed only by the division of pre-existing cells

There are a number of ways a sample can be prepared, these include:

     -Dry mount

     -Wet mount

     -Squash slides

     -Smear slides  

A solid specimen is viewed whole or cut into very thin slices (known as sectioning).

The specimen is placed on the centre of the slide and a cover slip is placed over the sample.

Examples are hair, pollen and dust (viewed whole) with muscle tissue and plants viewed sectioned.

A specimen is suspended in a liquid (eg. water or an immersion oil).

A cover slip is placed on from an angle.

Aquatic samples and other living organisms can be viewed this way.

A wet mount is prepared first.

Two microscope slides can be used to squash the sample as this avoids damage to the cover slip.

Squash slides is a good technique for soft samples.

Root tip squashes are used to look at cell division.

The edge of a slide is used to smear the sample which creates a thin, even coating on another slide.

A cover slip is then placed over the sample.

An example of a smear slide is a sample of blood which is a good way to view the cells in the blood.

Staining helps to distinguish between different components and makes the sample more visible.

A lot of biological material is not coloured which makes this effective.

Chemicals bind to the specimen allowing it to be seen.

Some stains are specific to cell structures (eg. Acetic orcein stains - DNA dark red).

A specimen is dehydrated with alcohols and then placed in a mould with wax or resin to form a hard block.

This can then be thinly sliced.

Not all materials can be sectioned as some material distorts when you try and cut it into thin sections.

The light from the lamp reflects off the mirror and passes through the condenser lens.

The specimen must be thin enough to let light pass through into the objective lens, where it is magnified and then into the eyepiece, where it is focused.