MicroscopySpec 4.1.1.5
Microscopy techniques have developed over time. The first microscopes used light and lenses to magnify a specimen, and these light microscopes were improved with better lenses and the use of stains. Later, electron microscopes were developed. These use electrons instead of light.
An electron microscope has much higher magnification and resolving power than a light microscope. This means that it can be used to study cells in much finer detail. This has enabled biologists to see and understand many more sub-cellular structures.
| Light microscope | Electron microscope | |
|---|---|---|
| Magnification | Lower | Much higher |
| Resolving power (resolution) | Lower | Much higher |
| Detail seen | Cells and larger sub-cellular structures such as the nucleus | Much finer detail, including the internal structure of mitochondria and chloroplasts, and ribosomes |
- Magnification
- How many times larger the image is than the real object.
- Resolving power
- The ability to distinguish between two points that are close together as separate points. Higher resolving power gives a sharper, more detailed image.
Magnification calculations
Rearranged: real size = image size ÷ magnification, and image size = real size × magnification. Make sure the image and real object are in the same units before you divide, then convert at the end. Give the answer in standard form if appropriate.
Calculating magnification
A drawing of a cell is 45 mm wide. The real cell is 0.15 mm wide. Calculate the magnification.
- Both sizes are in mm, so no conversion is needed.
- magnification = 45 ÷ 0.15 = 300.
Answer: × 300
Calculating real size
A cell appears 12 mm wide in an image magnified × 400. Calculate the real width in µm.
- real size = image size ÷ magnification = 12 ÷ 400 = 0.03 mm.
- Convert to µm: 0.03 × 1000 = 30 µm.
Answer: 30 µm
Quick check
How is the genetic material of a bacterial cell arranged?
Show answer
As a single DNA loop that is not enclosed in a nucleus. There may also be plasmids.
Which sub-cellular structure is the site of aerobic respiration?
Show answer
Mitochondria.
What is the formula for magnification?
Show answer
Magnification = size of image ÷ size of real object.
Why does an electron microscope show more detail than a light microscope?
Show answer
It has much higher magnification and resolving power.
Triple only: why are inoculating loops passed through a flame?
Show answer
To sterilise them and kill unwanted microorganisms.