Stage and
Stage Clips
Condenser
Diaphragm
Light Source
Base
Eyepiece lens
Nosepiece
Objective lens
Coarse adjustment knob
Fine adjustment knob

Part of microscope Function
Eyepiece Lens
Magnifies the specimen
Coarse Adjustment Knob
Used to focus on Low Power
Fine Adjustment Knob
Used to focus on Medium and High Power
Objective Lens
Magnifies the specimen
Nosepiece
Allows the objective lens to be changed
Stage Clips Holds the slide in place on the stage
Diaphragm Controls amount of light entering condenser
Condenser Concentrates light into a beam
Light Source Projects light upwards through microscope

• Microscopes have an eyepiece lens and several objective lenses.
• These objective lenses are normally referred to as Low,
Medium and High Power.
Total Magnification = Eyepiece Lens x Objective Lens
Example: Eyepiece Lens (x10)
Objective Lens (x4)
Total Magnification = (x10) x (x4)
= x40

Eyepiece Lens x10 x10 x10 x16 x16 x16
Objective Lens x10 x40 x16 x10 x40 x16
Total Magnification x100 x400 x160 x160 x640 x256

• The field of view is the area of the slide which can be seen when looking down through the microscope.
• The low power objective lens is ALWAYS used first because this allows a larger area of the slide to be seen.
• This then allows you to choose which part of the specimen on the slide you want to view in further detail at higher magnifications.
• Before increasing magnification the area you have chosen should be moved to the centre of the field of view.
(N.B. The following slides demonstrate this.)

• Using the low power objective lens and the coarse adjustment knob allows the word “ BIOLOGY ” to be seen clearly.
• If we wanted to look at the letters “ BIO ” more closely then the slide has to be moved so that these letters are centre of the field of view .

• Using the medium power objective lens and the fine adjustment knob allows the letters “ BIO ” to be seen clearly.
BIO
• If we wanted to look at the letter “ B ” more closely then the slide has to be moved so that this letter is centre of the field of view .

• Using the high power objective lens and the fine adjustment knob allows part of the letter
“ B ” to be seen in more detail.

• All living organisms are made of cells .
• Cells are the building blocks of life itself.
• Unicellular organisms: consist of ONE cell.
e.g. amoeba
• Multicellular organisms: consist of two or more cells.
e.g. earthworm

• Nucleus
– Controls ALL of the cells activities
• Cytoplasm
– Site of all of the chemical reactions
• Cell Membrane
– Controls the entry and exit of materials

• Nucleus
• Cytoplasm
• Cell Membrane
• Cell Wall
– Made of cellulose, provides support.
• Chloroplast
– Contains chlorophyll, essential for photosynthesis
• Sap vacuole
– Contains solution of sugars and salts

Slide Preparation and Staining
1. The material should be very thin to allow light to pass through it . Some types of material can be smeared onto the glass.
2. Most cell material is transparent and needs to be stained with one or more coloured dyes . This makes different parts of the cell stand out and easier to see.
3. The material should be covered with a coverslip to stop it drying out. The coverslip should be lowered with a mounted needle. This helps to prevent too many air bubbles being trapped in the preparation.
Stains
Examples of coloured dyes or stains which can be used to stain cells are: a) Iodine stain b) Methylene Blue stain

Onion cells under the microscope – low power

Onion cells under the microscope – medium power

Onion cells under the microscope – high power

• Cells are so small that they cannot be measured in millimetres !
• They are measured in micrometers ( µm )
• There are 1000 micrometers in a millimeter .
1mm = 1000 µm

• Convert the following measurements from mm into µm (Show your working) a.
2 mm b.
0.5 mm c.
0.04 mm d.
1.06 mm e.
0.072 mm f.
0.123 mm g.
0.88 mm h.
0.022 mm

a.
2 mm b.
0.5 mm c.
0.04 mm d.
1.06 mm e.
0.072 mm f.
0.123 mm g.
0.88 mm h.
0.022 mm x 1000 = 2000 µm x 1000 = 500 µm x 1000 = 40 µm x 1000 = 1060 µm x 1000 = 72 µm x 1000 = 123 µm x 1000 = 880 µm x 1000 = 22 µm

• Convert the following measurements from µm into mm (Show your working) a.
3000 µm b.
250 µm c.
86 µm d.
900 µm e.
47 µm f.
505 µm g.
1050 µm h.
636 µm

a.
3000 µm b.
250 µm c.
86 µm d.
900 µm e.
47 µm f.
505 µm g.
1050 µm h.
636 µm

1000 = 3mm

1000 = 0.25 mm

1000 = 0.086 mm

1000 = 0.9 mm

1000 = 0.047 mm

1000 = 0.505 mm

1000 = 1.05 mm

1000 = 0.636 mm

Estimating Cell Size
160 cm

Estimating Cell Size
To estimate the size of a cell you need to know:
• The diameter of the field of view
• The number of cells which fit across the diameter of the field of view

Estimating Cell Size
0.9 mm

Estimating Cell Size
Estimate of cell size
=
Diameter of the Field of View
Number of cells that fit across
=
900 µm
6
=
150 µm
The estimated size of the cell is 150 µm.