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Microscopy:
5.
The scale of things in biology - orders of magnitude
- comparison of
cells with other objects with
approximate size dimensions
Doc Brown's Biology exam study revision notes
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There are various sections to work through, after 1 they can be read and studied in any order.
INDEX biology notes: investigations using
microscopes
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(5) The scale of things
in biology and orders of magnitude
Comparison of cells with other objects with
approximate dimensions
The practical limit of magnification for an optical light
microscope is x1000 to resolve features e.g. structural parts of
cells.
In terms of dimensions we are talking about ~0.5
µm, the size of a larger virus.
Electron
microscopes can resolve images down to ~0.2 nm, the size of a
small atom.
This is a
resolving power 25 000 times greater than that of an optical
light microscope.
| Object |
Size |
|
Object |
Size |
| a common
ladybird |
~7 mm, 7000
µm |
|
HIV virus |
~0.1
µm,
~100 nm |
| diameter of a
human hair |
~0.1 mm, ~100
µm |
|
thickness of
cell membrane |
~0.007
µm, ~7 nm |
| typical plant
leaf cell |
~0.07 mm, ~70
µm |
|
diameter of
DNA strand |
~2.5 nm |
| diameter of
red blood cell |
~0.007 mm, ~7
µm, 7000 nm |
|
diameter of a
carbon atom |
~0.34 nm |
When comparing the size of
small objects like cells, scientists refer to differences in sizes as an
order of magnitude.
This means that an object is
described as being greater of smaller by a factor of 10.
For example, the leaf cell size
is one order (10 x) in size than a red blood cell.
The common ladybird is two
orders greater (100 x or 10 x 10) in size than a plant leaf
cell.
The thickness of the cell
membrane is three orders smaller {1/1000 or 1/(10 x 10 x10)}
than the diameter of a red blood cell.
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