The diagram shows the size of a selection of organisms, different cells and other structures.
We can compare sizes using a straightforward calculation.
For instance, the length of the leaf cell above is ten times the diameter of a red blood cell.
The calculation would be:
When comparing the size of a bacterium with the Human Immunodeficiency Virus (HIV) different units have to be converted to be consistent.
The length of the bacterium = 70 μm = 70 000 nm
The diameter of the HIV = 100 μm = 100 000 nm
Therefore the length of the HIV is times that of the bacterium. This means they differ by one order of magnitude.
What is the width of a cheek cell compared with a Salmonella bacterium?
140 times the size.
Differences in size are often described as differences in order of magnitude. That's the difference calculated in factors of 10.