GCSE · Biology · Edexcel · Spec 1BI0

Microscope technology and electron microscopy

Zoom into a phone photo far enough and it stops getting more detailed: it just turns into bigger blobs. Microscopes hit exactly the same wall.

Biology · Cell structure

One cell, two microscopes

View: Light microscope. Showing 2 layers: Cell, Light microscope view

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Explore

Switch between the two views, then tap a structure to see which microscope shows it.

Light microscope, magnifying up to about ×2000. You can make out the cell's outline, the nucleus and the chloroplasts, and that's where the detail runs out.

An illustration of what each microscope can show, not drawn to scale.

Magnification or resolution?

Can't see the mitochondria? Just zoom in more?

Your light microscope is at its highest magnification and you still can't see any mitochondria. A friend says: "Take a photo and blow it up ten times bigger on the computer. Then you'll see them."

Which is closest to what you think right now?

My friend's right. Make the picture big enough and the mitochondria will show up.It won't work. The problem isn't how big the image is, it's that the light microscope can't separate details that close together.Resolution just means how many times bigger the image is, so a bigger photo has a better resolution.

How sure are you?

I'm sureI think soI'm guessing

My friend's right. Make the picture big enough and the mitochondria will show up.

This is a common misconception

It feels as if it should work, but think about what enlarging a photo does. It takes exactly the detail that's already there and spreads it over a bigger area. If the microscope couldn't separate those fine structures in the first place, you just get a bigger blur. Magnification makes things look larger. It can't add detail that was never there.

It won't work. The problem isn't how big the image is, it's that the light microscope can't separate details that close together.

This matches the evidence

Exactly right. That's resolution: the minimum distance apart two points can be and still be seen clearly as separate points. It decides how much detail you can see. Think of a car's headlights at night. Far away they blur into one light, and blowing up a photo of them won't split them into two. The light microscope's resolution isn't fine enough to pick out mitochondria, so no amount of enlarging will show them.

Resolution just means how many times bigger the image is, so a bigger photo has a better resolution.

This is a common misconception

That's the meaning of magnification, not resolution, and the two get swapped all the time. Resolution is the minimum distance apart two points can be and still be seen as separate. Blowing up the photo doesn't change that distance at all, so the resolution stays exactly the same.

Magnification makes an image bigger; resolution decides how much detail is in it. Higher resolution is what lets an image at higher magnification stay clear.

Why electrons see more

Reason it through

Why can an electron microscope show structures that a light microscope can't?

Link 1 of 4

First link · your turn

Start with the one big design change. What does an electron microscope use to make its image?

Locked — reveal the link above first

How we got here

Put the story of the microscope in order

Put these in the order they happened, earliest first. Move each one with its ▲ and ▼ buttons, then lock in your order.

1 · Earliest4 · Most recent

Robert Hooke publishes Micrographia and uses the word 'cell'
Electron microscopes show sub-cellular structures in fine detail
Nobody knows that cells exist
The light microscope is invented

Your turn

Explain it in your own words

Explain how electron microscopy has increased our understanding of sub-cellular structures. [4 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

Electrons have a much smaller wavelength than visible light. (1 mark)
This gives electron microscopes a much higher resolution than light microscopes. (1 mark)
Structures too small for a light microscope to show, such as mitochondria, can now be seen. (1 mark)
Structures seen only in low detail before are now seen in fine detail, e.g. the double nuclear membrane or the nucleolus. (1 mark)

Model answer

Electrons have a much smaller wavelength than visible light, which gives electron microscopes a much higher resolution. Structures too small for a light microscope to show, such as mitochondria, can now be seen. Others that light microscopes showed only in low detail are now seen in fine detail: the nuclear membrane turns out to be a double membrane, and the nucleolus can be seen in detail. This has revolutionised our understanding of sub-cellular structures in eukaryotic cells, and in bacteria and viruses.

Cause first, then examples: say why electron microscopes resolve more, then name what that let us see for the first time.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Why an electron microscope shows you things inside a cell that a light microscope never will, however far you zoom in.

What you need to know

Most cells are too small to see without a microscope. Knowledge of cells began with the light microscope in the late 1500s, and Robert Hooke's Micrographia (1665) gave us the word 'cell'.
Magnification makes an object look bigger. Resolution, the minimum distance apart two points can be and still be seen as separate, decides how much detail you can see.
Electron microscopes use electrons, whose wavelength is much smaller than light's, so they have a much higher resolution and magnification than light microscopes.
There are two types, TEM and SEM, and between them they revealed sub-cellular structures in far finer detail than ever before.

The big picture

Magnification makes an object look larger; resolution, the minimum distance apart two points can be and still be seen as separate, decides how much detail you see. A light microscope (up to about ×2000, resolution about 0.2 micrometres) shows cells, the nucleus and chloroplasts, but not mitochondria. Electron microscopes use electrons, whose much smaller wavelength gives a resolution of about 0.002 micrometres. A TEM fires electrons through an extremely thin slice for flat images of the inside of cells; an SEM scans the surface to build 3D images of whole cells. That extra detail revolutionised our understanding of sub-cellular structures.

Key points

1Light microscope: visible light and glass lenses, magnification up to about ×2000, resolution about 0.2 micrometres.

2A light microscope shows cells, the cell membrane outline, the nucleus and chloroplasts, but not smaller sub-cellular structures such as mitochondria.

3Electron microscope: a beam of electrons with a wavelength up to 100,000 times smaller than visible light's, giving a resolution of about 0.002 micrometres.

4Higher resolution means images at higher magnification can be viewed clearly. Magnifying beyond what the microscope can resolve only gives a bigger blur.

5TEM: electrons through an extremely thin slice, giving flat two-dimensional images of sections that show the inside of cells. SEM: electrons scanned across the surface, building three-dimensional images of whole cells.

6Electron microscopy showed the nuclear membrane to be a double membrane and the nucleolus in detail, revolutionising our understanding of sub-cellular structures in eukaryotic cells, and in bacteria and viruses.

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Worked example

Problem

A scientist has three jobs. Choose the right microscope for each: (a) check whether the cells in a sample have a nucleus; (b) find out whether the membrane around a nucleus is single or double; (c) get a three-dimensional image of the outside of a whole cell.

⚠ Watch out

Saying electron microscopes show more detail because they magnify more. Magnification on its own just gives a bigger blur. The real reason is their much higher resolution, which comes from the electrons' much smaller wavelength.

🧠

Memory hook

Magnification makes it bigger; resolution makes it clearer. And for the two electron microscopes: TEM goes Through a thin slice, SEM Sweeps the Surface.

✓

Check yourself

Cover the page. In one sentence each, say what magnification means and what resolution means. Then say which of the two explains why an electron microscope can show mitochondria.

Flashcards

(13)

When did knowledge of cells begin, and why then?

With the invention of the light microscope in the late 1500s, because most cells are too small to be seen without a microscope.

What did Robert Hooke publish in 1665, and which word do we owe to him?

Micrographia, with images of objects seen with a light microscope. He is the first known person to use the word 'cell'.

How does a light microscope produce a magnified image?

It uses visible light and a system of glass lenses.

What does magnification mean?

Making a small object appear larger, in order to see more detail.

What is resolution?

The minimum distance apart two points can be and still be seen clearly as separate points. It decides how much detail can be seen.

Maximum magnification and resolution of a modern light microscope?

Magnification of about ×2000; resolution of about 0.2 micrometres.

What can a light microscope show in a cell, and what is too small for it?

It shows cells, the cell membrane outline, the nucleus and chloroplasts. It can't show smaller structures such as mitochondria.

Why do electron microscopes have a much higher resolution than light microscopes?

Electrons have a much smaller wavelength than visible light, up to 100,000 times smaller.

Roughly what resolution can an electron microscope reach?

About 0.002 micrometres.

Why does a higher resolution matter?

It means images at higher magnification can still be viewed clearly.

TEM: how does it work, and what image does it give?

It fires electrons through an extremely thin slice of the specimen, giving flat, two-dimensional images of sections that show the inside of cells.

SEM: how does it work, and what image does it give?

It scans electrons across the surface of the specimen and can build three-dimensional images of whole cells.

What did electron microscopes reveal about the nucleus?

That the nuclear membrane is a double membrane, and the nucleolus in detail.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Microscope technology and electron microscopy

Can't see the mitochondria? Just zoom in more?

Light, TEM or SEM?

Put the story of the microscope in order

Explain it in your own words

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