Most animal and plant cells are 0.01 – 0.10 mm in size. The smallest thing seen with the naked eye is about 0.05 mm.
For all cells we need a microscope to see them in any detail.
The best unit to measure most cells is the micrometre, symbol μm.
One metre can be broken down into the following measurements:
|Millimetre, mm||Micrometre, μm||Nanometre, nm|
|Division of a metre as a fraction|
|Division of a metre in standard form||1 × 10-3 m||1 × 10-6 m||1 × 10-9 m|
When writing and working with very large or very small numbers, we use standard form.
Standard form shows the size of numbers as powers of ten.
In a book, a micrograph of the cell measured 100 mm.
The real size of the cell shown is 0.05 mm.
To calculate the magnification:
It’s important to work in the same units when calculating magnification. Sizes of most cells are given in micrometres, symbol μm.
To calculate magnification using the same formula in micrometres, convert the measurement of the cell above from mm into micrometres:
Cell measurement = 100 mm
1 mm = 1000 μm
100 mm = 100 x 1000 μm
100 mm = 100 000 μm
The real size of the cell above in micrometres is 50 μm.
The magnification of the image:
From this we know that the image has been magnified 2000 times.