1.1.41 · Cell Structure

Resolution and Magnification — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

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📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision

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1.1.4 Resolution and Magnification — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Distinguish magnification from resolution and explain why electron microscopes resolve more detail than light microscopes.Definition — the number of times a specimen is enlarged to gi…

Light microscope lenses
Total magnification
Low resolution
Limit on useful magnification
Simple rule
Wavelength

Part 1 of 6Magnification

Definition

Definition the number of times a specimen is enlarged to give an image.

Light microscope lenses

Light microscope lenses an eyepiece lens (often x10) and objective lenses.
- (x4, x10, x40, x100)

Total magnification

Total magnification eyepiece magnification × objective magnification.

Part 2 of 6Resolution

1Definition

Definition the ability to distinguish two points close together as separate objects.
It determines how much detail can be seen.

2Low resolution

Low resolution two separate objects appear as one point and the image looks blurred.

3Limit on useful magnification

Limit on useful magnification magnifying beyond the resolution limit does not reveal more detail.

4Simple rule

Simple rule magnification makes things bigger, whereas resolution makes things clearer.

Part 3 of 6Why wavelength limits resolution

Light microscope

Light microscope it cannot resolve points closer than about half the wavelength of light.
Visible light is 400–700 nm, so the limit is about 200 nm.
A phospholipid bilayer is about 7 nm wide, so it cannot be seen.

Electron microscope

Electron microscope electrons have a much smaller wavelength than light.
Resolution reaches about 0.5 nm, so much higher useful magnification is possible.

Part 4 of 6Comparing light and electron microscopes

Feature	Light microscope	Electron microscope
Radiation	Visible light	Electron beam
Resolution	About 200 nm	About 0.5 nm
Lenses	Glass	Electromagnets
Specimen	Can be living	Dead, in a vacuum
Image	Colour	Black and white (false colour added)

TEM

TEM electrons pass through a very thin stained section to give a 2D internal image.

SEM

SEM electrons scattered from a metal-coated surface give a 3D image of the surface.

Part 5 of 6More from the specification

Microscopic resolution of specimen sample

Microscopic resolution of specimen sample shorter illuminating wavelengths increase optical resolution, distinguishing submicron organelle details within the prepared specimen sample.

Magnification Equation and Units Conversion

The relationship between image size I, actual specimen size A,
and magnification M is defined by the equation M = I / A; all linear dimensions must be converted to identical units before computing values.
- (e.g., 1 mm = 1000 µm)

Calibrating Eyepiece Graticule with a Stage Micrometer

To measure cells accurately on a microscope slide, an eyepiece graticule scale is calibrated by aligning its divisions against the known physical scale divisions of a stage micrometer at each specific objective magnification.

Biological Drawing Conventions and Scale Bars

High-quality biological drawing of cells requires clear continuous lines, no shading, proportional cell walls,
and an included scale bar showing the actual dimensions calculated from graticule units.

Magnification Equation and Units Conversion

The relationship between image size I, actual specimen size A,
and magnification M is defined by the equation M = I / A; all linear dimensions must be converted to identical units before computing values.
- (e.g., 1 mm = 1000 µm)

Calibrating Eyepiece Graticule with a Stage Micrometer

To measure cells accurately on a microscope slide, an eyepiece graticule scale is calibrated by aligning its divisions against the known physical scale divisions of a stage micrometer at each specific objective magnification.

Biological Drawing Conventions and Scale Bars

High-quality biological drawing of cells requires clear continuous lines, no shading, proportional cell walls,
and an included scale bar showing the actual dimensions calculated from graticule units.

Magnification factor

The µm per graticule division at a given objective lens.

Starch grain

Store of starch in the stroma.

Graticule

An eyepiece scale calibrated against a stage micrometer to measure specimens.

Micrometer

A unit of length; 1 mm = 1,000 micrometers

Coverslip

A thin glass or plastic square placed over the specimen to flatten it and protect the lens.

Starch

An insoluble polysaccharide of glucose used by plants for energy storage.

Eyepiece graticule

A scale in the eyepiece that is calibrated with a stage micrometer to measure specimens.

Graticule division

One division of the eyepiece graticule scale.

Biological drawing

A labelled, clear line drawing recording what is observed.

Stage micrometer

A slide with an accurately known scale used to calibrate the graticule.

Part 6 of 6More on this topic

Confusing magnification with resolution — magnification enlarges, resolution gives detail.

Resolution

Resolution the smallest distance at which two points are seen as separate.

Key terms

Term	Meaning
Magnification	The number of times larger an image is than the real object.
Resolution	The ability to see two close points as separate; the level of detail visible.
Wavelength	The distance between wave peaks; shorter wavelengths give better resolution.
Total magnification	Eyepiece magnification multiplied by objective magnification.
Electron microscope	A microscope using an electron beam that gives much higher resolution than light.
TEM	Transmission electron microscope showing thin internal sections.
SEM	Scanning electron microscope showing surfaces in 3D.

Avoid these mistakes

Assuming greater magnification always reveals more detail — resolution sets the limit of detail.

Saying resolution means making an image bigger — that is magnification.

Saying electron microscopes have higher resolution because of higher magnification — it is the shorter wavelength of electrons.

Saying electron microscopes can view living cells — specimens must be in a vacuum.

Last updated: 18 October 2026