comparing sizes

• 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.
• The limits of the light microscope are a factor in understanding cell structure.
• Animal cells and plant cells are different in terms of their structure and function.
• Sizes of organisms, cells, and other structures can be compared using a straightforward calculation.
• The length of the leaf cell is ten times the diameter of a red blood cell.
• 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 is 1 μm, which is 1000 nm.
• The diameter of the HIV is 100 nm, so the length of the bacterium is \(\frac{1000}{100}\) = 10 times that of the bacterium.
• The width of a cheek cell is 140 times the size of a Salmonella bacterium.
• Differences in size are often described as differences in order of magnitude.
• For each order of magnitude, a number is ten times the previous one.