Microscopesmagnifications, resolutions and

calculations

Light microscope- uses light and

lenses to enlarge tiny objects

Pollen grains – light microscope

Electron microscope - electromagnetic lenses are used to direct electrons onto the tiny specimen

Pollen grains –scanning electron microscope 3D

ABPI -

• http://www.abpischools.org.uk/topic/cellbiology/2

The difference betweenmagnification and resolution.

• Magnification is the degree to which the size of an image is larger than the object itself.

• Resolution is the degree to which it is possible to distinguish between two objects that are very close together.

The electron microscope has higher magnification and resolution

Radiolarian = single celled protozoan found in oceans part of zooplankton

Moth - eye = 800micrometres

hydrothermal worm taken at 525 times magnification

How do we find the overall magnification of a light

microscope?

Eyepiece

Magnification

Objective

Magnification

Overall

Magnification

X10 X4

X10 X10

X10 X40

X10 X100

Eyepiece

Objective lens

40

100

400

1000

10001000

10001000

mm

Micrometre

nm

Magnification

Magnification= size of image/ actual size of specimen (must be in same units)

What can we see with a microscope?

Typical sizes

• Examples of typical sizes:• 10-100µm: cells of eukaryotes• 1-10µm: organelles• 1µm: bacteria (size vary)• 100nm: viruses (size vary)• 10nm: thickness of cell membranes• 2nm: DNA molecule in human choromosome• 1nm: molecules• 0.1nm: atoms

Nanometre Micrometre Millimetre

5 0.005 0.000005

1

1

1

3

7

0.5

0.001 0.000001

1000 0.001

1 000 000 1000

3000 0.003

0.007 0.000007

500 000 500

Magnification

Magnification= size of image/ actual size of specimen (must be in same units)

The diagram below is a drawing of an organelle from a ciliated cell as seen with an electron microscope.

Calculate the actual length of the organelle as shown by the line AB in the diagram. Express your answer to the nearest micrometer (μm).

Show your working.

Answer = ........................................... mm

A B

× 20 000

A = I

M =102mm20000 =

102000mm20000

5.1

Magnification of Cheek cells

Actual size of cheek cells = 60μm

First – change to mmTo change μm to mm we need to ÷ by 1000

So 60μm = 0.06mm

Size of this skin cell =Size in mm =

SoMagnification = size of image / actual size =

Magnification = /0.06mm =

The diagram below is a drawing of an alveolus together with an associated blood capillary.

The line AB in the diagram represents an actual distance of 1.5 µm.

Calculate the magnification of the drawing. Show your working.

Answer = × .................................................

A

cell X

blood

capillary

alveolus lined with

squamous epithelium

B

M = IA

=21mm1.5mm

=21000mm

1.5mm

14000

ABPI -

• http://www.abpischools.org.uk/topic/cellbiology/2