Cell structure
Organisms are made up of cells. Most organisms are multicellular and have cells that are specialised to do a particular job. Microscopes are needed to study cells in detail.
Cell measurement
Greg Foot explains the main differences between light and electron microscopes
Light microscopes
Cells range in size:
- animal cells are between 0.01 mm – 0.05 mm
- plant cells are between 0.01 mm – 0.10 mm
The human eye can see objects as small as around 0.05 mm. A microscope is required to see cells in any detail.
Microscopes magnify the image of a biological specimen so that it appears larger. The type of microscope used in a school laboratory is a compound microscope.
Calculating the magnification of the microscope
The compound microscope uses two lenses to magnify the specimen – the eyepiece and an objective lens.
In most microscopes, there is a choice of objective lenses to use. Magnification can be varied according to the size of the specimen and the level of detail required.
The magnification of a lens is shown by a multiplication sign followed by the amount the lens magnifies, eg ×10.
So, if the magnification of an eyepiece is ×10 and the objective is ×4, the magnification of the microscope is:
magnification of eyepiece × magnification of objective
= 10 × 4
= 40
- Question
If the magnification of an eyepiece is ×10 and the objective is ×40, what is the magnification of the microscope?
×400.
Calculating the magnification of an image
Microscopes use lenses to magnify the image of a biological specimen so that it appears larger.
The formula to calculate magnification is:
\[magnification=\frac{size\; of\; image}{real\; size\; of\; image}\]