Romans in the First Century were the first to make glass. Since then, scientists have been trying to magnify objects.
No-one knows who first invented the microscope but there have been key stages as it developed:
Throughout their development, the magnification of light microscopes has increased but very high magnifications are not possible. The maximum magnification with a light microscope is around x1500.
The magnification of a microscope is not the only factor that is important when viewing cells. The detail that can be seen is also important.
The ability to see an image in greater detail depends on the resolution or 'resolving power' of the microscope. Resolution is the ability to see two points as separate points, rather than seeing them as a single point.
Think about a digital photo. It can be enlarged but over a certain size, you won't be able to see any more detail. It will just become blurry.
The maximum resolution of a light microscope is around 0.2 μm, or 200 nm. This means that it cannot distinguish two points closer than 200 nm. One nm, or nanometre, is one billionth of a metre. This is written as or in standard form as 1 × 10-9 m.
The resolution of the light microscope is limited by the wavelength of light.
Light microscopes also have a shallow depth of field. When the light microscope is focused on the structure to be examined, the objects above and below it appear blurred.
Electron microscopes use a beam of electrons instead of light rays.
There are two types of electron microscope:
TEMs have a maximum magnification of around ×1 000 000, but images can be enlarged beyond that photographically. The limit of resolution of the TEM is now less than 1 nm.
The TEM has revealed structures in cells that are not visible with the light microscope but an electron microscope can only examine dead tissue.
The scientists Schleiden and Schwann observed plant and animal tissues under the microscope and both described similar cellular structures. They developed 'cell theory' as a result of their studies and proposed that cells are the basic unit of life. However, they were unaware of cell division and thought that new cells formed in a similar way to crystals.
Further advancements of the microscope allowed scientists to study cells in detail and build on the work of Schleiden and Schwann. Cell theory now states: