Measurement Symbol Unit

Metre m 1m

Millimetre mm 10-3m

Micrometre mm 10-6m

Nanometre nm 10-9m

1mm = 1000m 1m = 1 000

000m

So 1m = 10-6m1m = 1000 nm

So 1nm = 10-9m

This is the extent to which an object has been This is the extent to which an object has been enlarged.enlarged.

condenser lenscondenser lens

• Magnifying an object reveals further structural detail.

• Although magnification can be increased ad infinitum it will not necessarily produce more detail.

• The amount of detail is due to the resolving power or resolution of a microscope.

Is the ability to see 2 adjacent, but separate, points as distinct entities following magnification.

0.2mThis is a major limitation of using the light microscope.

The electron microscope has a higher resolution and can distinguish 2 points that are only 0.1nm apart.

This is because light has a longer wavelength than electrons.

Both objects seen separatelyas they fall

in different wavelengths

Both objects seen as a single fused image

as they both fall in the same wavelength

light

electron

Light sees one point (inside one wavelength)Electron sees 2 distinct images (different

waves)

ELECTROMAGNETIC

ELECTROMAGNETIC

ELECTROMAGNETIC

Coloured images are obtained using computer software As electrons do not show colour.

TRANSMISSION ELECTRON MICROSCOPE Electrons pass through very thin specimens, giving very high resolution and

therefore very high magnifications are possible

SCANNING ELECTRON MICROSCOPE Electrons are reflected off the surface of the specimen. The resolution and

magnification is not as high, but SEM PRODUCES 3D IMAGES

Comparison of light and electron microscopes

Light microscope Electron microscope

Radiation used Light rays Electron beams

Magnification X2000 X1000 000

Resolving power 0.2mm 0.1nm

Focused by Glass lenses Electromagnets so needs vacuum as electrons deflected by air

Bio material Living or dead Dead (in vacuum)

Prep of material Quick & simple Time consuming complex: special cutting apparatus needed & special stains. This may lead to distortion of the bio material forming artefacts.

Highlight the advantages and disadvantages of each type of microscope

I = IMAGE SIZE

M = MAGNIFICATION

A = ACTUAL SIZE

Calculating magnification, image and object size from a micrograph

MAGNIFICATION =IMAGE SIZE

ACTUAL SIZE

1. An object on an electronmicrograph is measured as 12mm, but has an actual size of 2.3mm. Calculate the magnification.

2. An organelle measures 21mm at a magnification of X 18 000. Calculate the actual size of this organelle.

3. An organelle has an actual size of 0.7 mm. Calculate the image size when it is magnified X 150 000

• Measure the length of the scale bar in mmThis is the image size.

• Read the length given on the scale barThis is the actual size

• Find the magnification Use the equation M = I/A

Preparation and staining of temporary mounts

Making microscope drawings

• Clear and accurate Clear and accurate sharpsharp pencil line drawings pencil line drawings

• NoNo shading or colour shading or colour

• Label clearly and accuratelyLabel clearly and accurately

• Plan your drawing ensure parts are Plan your drawing ensure parts are in proportionin proportion and fit page and fit page

• Draw a faint outline showing relative position of partsDraw a faint outline showing relative position of parts

• Complete final outline and details with clear firm lines.Complete final outline and details with clear firm lines.

• Be as accurate as possibleBe as accurate as possible

• Ensure labels are added in pencil and not too close to the Ensure labels are added in pencil and not too close to the drawingdrawing