The Light Microscope

The light microscopeEyepiece lens

Coarse adjustment knob

Fine adjustment knob

Nosepiece

Stage and Stage ClipsCondenserDiaphragm

Light SourceBase

Objective lens

Parts of the microscopePart of microscope FunctionEyepiece Lens

Coarse Adjustment Knob

Fine Adjustment Knob

Objective Lens

Nosepiece

Stage Clips

Diaphragm

Condenser

Light Source

Used to focus on Medium and High Power

Magnifies the specimen

Used to focus on Low Power

Allows the objective lens to be changed

Holds the slide in place on the stage

Controls amount of light entering condenser

Concentrates light into a beam

Projects light upwards through microscope

Magnifies the specimen

Total Magnification• 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

Total MagnificationEyepiece Lens Objective Lens Total Magnification

x10 x10

x40 x400

x10 x160

x10 x160

x16 x40

x16 x256

x10

x100

x16

x16

x640

x16

Field of View• 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.)

Low power• 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.

BIOLOGY

BIOLO

Medium power• Using the medium power

objective lens and the fine adjustment knob allows the letters “BIO” to be seen clearly.

• 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.

BIO

High power• Using the high power

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

Cells• 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

Animal Cells• Nucleus

– Controls ALL of the cells activities

• Cytoplasm– Site of all of the

chemical reactions

• Cell Membrane– Controls the entry

and exit of materials

Plant Cells• 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 Staining1. 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.

StainsExamples 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

Magnified even further

Measurement• 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

Converting to micrometers• Convert the following measurements

from mm into µm (Show your working)

a. 2 mmb. 0.5 mmc. 0.04 mmd. 1.06 mme. 0.072 mmf. 0.123 mmg. 0.88 mmh. 0.022 mm

Converting to micrometers

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

Converting to millimeters• 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

Converting to millimeters

a. 3000 µm 1000 = 3mmb. 250 µm 1000 = 0.25 mmc. 86 µm 1000 = 0.086 mmd. 900 µm 1000 = 0.9 mme. 47 µm 1000 = 0.047 mmf. 505 µm 1000 = 0.505 mmg. 1050 µm 1000 = 1.05 mmh. 636 µm 1000 = 0.636 mm

Estimating Cell Size

160 cm

Can you estimate the size of the frog?

Estimating Cell SizeTo 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

Can you estimate the

size of the cell?

Estimating Cell SizeEstimate of cell size =

Diameter of the Field of View

Number of cells that fit across

= 900 µm6

= 150 µm

The estimated size of the cell is 150 µm.