Almost every question here comes down to one distinction: magnification is how much bigger, resolution is how much detail. Get that clear and you can answer anything they throw at you about light and electron microscopes.
📚 What you need to know
Magnification = how many times bigger the image is than the real object.
Resolution = the ability to see two very close objects as two separate things.
Light microscopes are limited to about 200 nm resolution, because you cannot resolve anything closer than half a wavelength of light.
Their maximum useful magnification is roughly ×1500.
Electrons have a far shorter wavelength, giving electron microscopes about 0.2 nm resolution — around 1000 times better.
TEM fires electrons through a very thin specimen: high detail, 2-D internal view.
SEM scans electrons across the surface: lower detail, 3-D surface view.
Electron microscopes need a vacuum, so specimens must be dead, and images are not in colour.
Magnification is not resolution
This is the single most tested idea on the page, so be precise about it.
Magnification makes things bigger. You can magnify anything as much as you like.
Resolution is about detail. It is the smallest distance two points can be apart and still be seen as two points rather than one blur.
Think of zooming into a photo on your phone. The picture gets bigger and bigger, but past a certain point you are just looking at bigger blurry blocks. That is magnification without resolution — and it is exactly why a light microscope stops being useful above about ×1500.
Why light runs out
You cannot resolve two objects that are closer together than half the wavelength of the light you are using. Visible light has a wavelength of roughly 400–700 nm, so the best a light microscope can manage is around 200 nm, or 0.2 µm.
Electrons behave as waves too, but with a much shorter wavelength — around 1 nm. That is why electron microscopes can resolve down to about 0.2 nm.
Everything to the left of the amber line is invisible to a light microscope. That is why ribosomes, lysosomes and the endoplasmic reticulum were only described once electron microscopes arrived.
What each one can see. A light microscope shows whole cells, nuclei, and (just about) mitochondria and chloroplasts. Ribosomes, endoplasmic reticulum and lysosomes are all too small — they need an electron microscope.
The two types of electron microscope
In a TEM, denser parts of the specimen absorb more electrons, so they show up darker. That contrast is what makes the internal structures visible.
Feature
Light microscope
Electron microscope
Uses
Light
A beam of electrons
Resolution
About 200 nm
About 0.2 nm
Useful magnification
Up to about ×1500
Up to about ×1 500 000
Specimens
Can be living or dead
Must be dead (vacuum needed)
Colour
Colour images
Black and white only
Preparation
Simple, quick
Complicated and slow
Cost and size
Small, cheap, portable
Large, expensive, fixed in place
Drawbacks worth naming
No living specimens. The vacuum removes all water, so anything inside dies before you look at it.
Artefacts. The long preparation can create structures that look real but were produced by the fixing and staining, not by the cell.
No colour. The colourful electron micrographs you see online have been coloured in afterwards.
Newer techniques.Cryogenic electron microscopy flash-freezes samples so individual molecules can be imaged and rebuilt in 3-D by computer. Freeze fracture freezes a sample and splits it apart, giving a flat view through the middle of a membrane. On the light side, fluorescent stains and immunofluorescence use dyes and antibodies to make specific molecules glow.
Worked examples
WORKED EXAMPLE
A ribosome is about 25 nm across. Explain why it cannot be seen with a light microscope. [3]
Step 1: state the limit
A light microscope has a resolution of about 200 nm.
Step 2: compare25 nm is far smaller than 200 nmStep 3: explain why the limit exists
You cannot resolve objects closer than half a wavelength of visible light, which is 400–700 nm.
Too small to be resolved – increasing magnification would not helpthe last line is the mark most students miss
WORKED EXAMPLE
Calculate how many times better the resolution of an electron microscope (0.2 nm) is than that of a light microscope (200 nm).
Step 1: divide the larger by the smaller200 ÷ 0.2 = 10001000 times bettera smaller resolution number means better resolution – that catches people out
WORKED EXAMPLE
A researcher wants to see the three-dimensional shape of a pollen grain’s surface. Suggest which microscope she should use, and give a reason. [2]
Step 1: choose
A scanning electron microscope (SEM).
Step 2: justify
The beam bounces off the surface, so it produces a three-dimensional image of the outside, and it can be used on thick specimens.
SEM – surface detail in 3-Da TEM would be wrong here: it needs a very thin slice and gives a flat internal view
💡 Exam tip
Define both terms cleanly: magnification is how many times bigger; resolution is how much detail.
Learn the four key numbers: 200 nm, 0.2 nm, ×1500, ×1 500 000.
TEM = through. SEM = surface and scanning. The first letters do the work.
If a question asks for an advantage of a light microscope, the strongest answers are living specimens and colour.
Say “cannot be resolved”, not “too small to see” — the exact wording matters here.
Mention artefacts when discussing why electron micrographs need careful interpretation.
⚠ Common mix-up
Saying higher magnification means more detail. Only better resolution gives more detail.
Thinking a bigger resolution value is better. It is the opposite — 0.2 nm beats 200 nm.
Claiming electron microscopes show living cells. The vacuum makes that impossible.
Mixing up TEM and SEM. TEM: thin slice, internal, 2-D. SEM: surface, 3-D.
Saying electron microscopes produce colour images. Any colour has been added afterwards.
Forgetting that a light microscope can just about show mitochondria and chloroplasts — it is smaller organelles it cannot manage.
Up next: General Cell Structure — the three things absolutely every cell has, whether it is a bacterium or one of your own.
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