By the end of this spread, you should be able 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.
The development of cell theory
In the 1660s, Robert Hooke developed a compound microscope using several lenses. He used it to examine slices of cork taken from under the bark of an oak tree. Hooke noted that the slices of cork were made up of a lot of tiny chambers. They resembled rooms, or cells, in which monks lived, so he called the tiny chambers in the corks "cells". With better microscopes, other scientists studied biological material and saw that all plant and animal material was made up of many cells. By the 1840s the Cell Theory - developed by two scientists, Schleiden and Schwann - was accepted. The Cell Theory, as extended by the work of Virchow in 1855 and Weismann in 1880, states:
- All living things consist of cells.
- New Cells are formed only by the division of pre-existing cells.
- The cell contains inform that acts as the instructions for growth. This information can be passed to new cells.
Investigating cell make-up
Cells are very small. Most are too small to be seen with the naked eye, and certainly not in any detail. In order to investigate cells, we need to be able to produce images that are both enlarged and more detailed. During the past 60 years, light microscopes have improved and electron microscopes have been developed. This has allowed scientists to study cells in detail. Other scientists have studied the chemical reactions going on in the different parts of cells. The results of these investigations have enabled us to understand how the structure of cell parts allows them to carry out their functions.
Magnification and resolution
In the dark, a car's headlights at some at some distance away appear as one light source - if you take a photograph it will also show one light source. You could enlarge the photograph many times but it would…