KNOWLEDGE AREA:
Life at Molecular, Cellular and
Tissue Level
TOPIC 1.2: Cells: The Basic
Unit of Life
A Brief Overview of the
History of Microscopy

Introduction
Structure of the Microscope
Care of the Microscope
Use of the Microscope
Magnification

 As we already know cells are microscopic.
What does this mean?

 That’s right !
 Microscopic: refers to organisms that are so small
that they are not visible to the naked.

TERM:
Microscopic
DEFINITION:
refers to organisms that are
so small that they are not
visible to the naked.
USE IN SENTENCE:
Viruses and bacteria are
microscopic.

 Scientists were able to see and study the cells
because of a discovery of microscopes.
 Initially botanist and zoologist were only able to
study, describe, draw and label only the external
structure of macroscopic organism.
 This is referred to as the macroscopic view.
What are macroscopic
organisms?

 That’s right …
 Macroscopic: refers to organisms that are visible
to the naked eye.

TERM:
Macroscopic
DEFINITION:
refers to organisms that are
visible to the naked eye.
USE IN SENTENCE:
Bees and butterflies are
macroscopic because you
can see with your eyes
only.

 Robert Hooke, an
English scientists looked
at cork tissue under a
very simple microscope
as shown alongside.
 He observed these cells
in 1665.
 As shown in the insert
he saw many box like
compartments.
 He called these
compartments cells.
Robert Hooke and his
microscopic study

 The cork tissue comes from the cork plant.
 However all he managed to see were the cell
walls of the cells.
 The cork cells were dead, therefore there was
nothing inside these cells.

 He was a Dutch
scientist.
 He observed the
bacteria under a
simple microscope
in 1674 as shown
below.
Anton van
Leeuwenhoek
Van Leeuwenhoek’s
simple microscope

 Three scientist, Oken in 1805, Lamarck in 1809
and Dutrochet in 1824, independently stated that
plants and animals were made up of cells.
 In 1838 Mathias Schleidan, a German scientist,
was first to regard the cell as a structural unit of
plants.
 Then in 1839, Theodor Schwann was the first to
regard the cell as the structural unit of animals.

 A German scientist, Purkinje, was the first to use
the term protoplasm to describe the living
contents of the cell. This was in 1839.
 Then 1859, another German scientist, Schultz,
was the first to describe the protoplasm as the
physical basis of life.
 Finally, Rudolf Virchow, put forward the idea that
new cells formed when existing cells divided.
 These scientist were able to make these
discoveries as a result of advancement in the
development of the microscope.

 These ideas mentioned in the previous two slides
developed into what is known as the cell
theory.

According to this theory:
1. Every living organism is made up of cells.
2. Every living cell comes from another.

 With your microscope at school you are able to
see objects magnified 600 times, by using the 40X
objective and 15X ocular lens.
 The nucleus, cell membrane, cytoplasm and
chloroplast were observed and named using the
light microscope.
 However the details of these structures were not
visible because the microscope is not powerful
enough.

 However in the 1930s a more powerful
microscope was invented by Zworykin.
 This was called the electron microscope

 There are 2 types of electron microscopes.
 They are the scanning electron microscope (SEM)
and the transmission electron microscope (TEM)
 The SEM is used to scan and view the surface of
objects.
 The TEM is used to see inside the objects by
allowing light to pass through them.

 With the electron
microscope we are able to
view objects 50 000 to 100
000 times.
 The image is clear and not
blurred.
 They are able to provide
such good images because
they use electron beams
instead of light
Electron Microscope

Parts of the Light Microscope

1. Base: supports the
microscope. Always
place your hand
under the base
when transporting
the microscope.
2. Mirror: provides
source of natural
light. The mirror
must be focused to
reflect light.
Parts of the Light Microscope

3. Illuminator/lamp: it
provides an electric
source of light, it is
much easier to use.
4. The condenser: it is
found below the stage.
Its function is to
concentrate the light
through the slide and
specimen.
5. Iris diaphragm: this is
an opening in the
condenser, it controls
the amount of light
falling on the specimen. Parts of the Light Microscope

6. Stage: this is the
platform on which the
slide is placed.
7. Stage/slide clips: these
are metal clips that are
used to hold the slide in
position so that is does
not move around when
it is being focused.
8. Mechanical stage: this
is found in only some
microscopes, it allows
easy movement of the
slide.
Parts of the Light Microscope

9. Objectives: these are a
combination of lenses
used to magnify the
specimen. There are 3
different types of
objectives.
10. 4X objectives: this is
the short objectives. It
magnifies the objectives
4X
11. 10X objectives: this is
the medium objective.
It magnifies the
specimen 10X.
Parts of the Light Microscope

12. 40X objective: this
is the long objective.
It magnifies the
specimen 40X
13. The revolving nose
piece: the
objectives are
attached to this nose
piece. Ensures the
objective is in
position when
viewing the
specimen.
Parts of the Light Microscope

14. Body tube: the eye
piece and objectives are
found on it. It also links
the eye piece and
objectives. In other
words it links and
supports the optical
parts.
15. Coarse adjustment
screw: used to make
adjustments to focus
the image. It moves the
body tube up and down
quickly, it provides quick
focus. Used mainly at
low magnification.
Parts of the Light Microscope

16. Fine adjustment screw:
is used to make fine
adjustments to focus
the image. Used with
higher magnification.
Prevents damage to
slide if any sudden
movements are made
during focusing.
17. Eye piece/ocular:
combination of lenses
that are used to magnify
the specimen. There
are 3 oculars 5X, 10X
and 15X
Parts of the Light Microscope

Use your notes and diagram of the microscope to
label the diagram and provide the functions of the
following parts:
1. A
2. C
3. E
4. I
5. M

A. Eyepiece
B. Coarse adjustment screw
C. Body tube
D. Fine adjustment screw
E. Nose piece
F. Medium objective/10X
G. Arm
H. Long objective/40X
I. Stage
J. clip

K. Diaphragm
L. Base
M. Light source
N. Short objective/4x
1. Eye piece-magnifies image
2. Body tube- supports and links optical parts
3. Nose piece- attachment of objectives
4. Stage- platform on which slide is place
5. Light source- provides electrical light

Follow these guidelines when handling a
microscope:
1. Transport the microscope by placing one hand
under the base and the other holding the arm,
2. Work one hand width away from the edge of
the work bench.
3. Use only soft tissue to clean the lens.
4. Always ask for help if you are unsure of anything

Setting the light and condenser
1. Open the diaphragm fully.
2. Look at the mirror. Notice that it has two
surfaces: a plane one and a concave one. If the
microscope has a built in condenser then have
the plane surface of the mirror facing up. If the
there is no condenser then the concave surface
must face up.
3. Adjust the mirror so that it faces a source of
natural light. E.g. A window, open door.

4. Select the lowest power objective by turning the
nose piece until you hear or feel the object click
into position.
5. Place a sharp pencil on the mirror and focus
until you obtain a sharp image of the pencil tip.

Focusing at low magnification
1. Place the slide on the stage.
2. Secure it using the clips.
3. Look through the eyepiece and slowly turn the
coarse adjustment screw to focus the specimen.
4. Slowly turn the fine power objective to focus a
clearer image of the specimen.
5. The slide may need to be moved to ensure the
part of the specimen under examination is what
you are seeing.

Focusing at higher magnification
1. Move the next objective into position by
carefully moving the nose piece until the
objective clicks into position.
2. If the specimen is not clearly visible then use the
fine adjustment screw to obtain a clearer image.
3. You may repeat the process using the next high
power object if more detail is required.

Changing the eyepiece
1. The magnification can be increased by using
higher power eyepieces.
2. Simply remove the existing eyepiece and replace
it with one that has higher magnification power.

Record what you see
1. Draw a diagram of what you see.
2. Draw and label exactly what you see, even if
many aspects are missing.
3. In many cases you do not have to draw the
entire image, only a portion of it.
4. Do not forget to indicate the scale of your
drawing. For example if you used the medium
power objective and the 5X eyepiece then your
scale is 150 times(5X10)
5. Use a sharp pencil.

1. Remove the slide.
2. The 4x objective must be in position.
3. Replace the dust cover
4. Place the microscope in the correct box.
5. Store away.

Magnification of the microscope when viewing an
objective:
 In order to determine how many times the
specimen viewed is magnified by we need to
calculate the magnification of the microscope.
 We can do this by using the following formula:
Magnification power of = magnification of eyepiece X magnification
of microscope lens

 For example if you use the 10X eyepiece and the
40X objective then…
Magnification = 10 X 40 = 400X
 It is usually expressed as “viewed under the
microscope at 400X.”

To determine the actual size of an object viewed
under the microscope using the field of view
approach.
 The field of view is the circle of light that you see
when looking through the eyepiece.
 The diameter maybe measured by viewing a ruler
under the microscope.
 The diameter for the field of view and the lens on
your microscope is about 4.5 mm or 4500μm.

 To calculate the length of the object you must
determine the portion/fraction of the
field it covers.
 This can only be done by determining the number
of objects that can fit in the field of view.

For example look at the two field of views below.
 In the one on the right 4 of the object can fit in
the field of view.
 Therefore one object occupies ¼ of the field
diameter.
X
X
X
X
X

 Therefore the approximate length of the object
can be calculated as follows:
4500 μm X ¼ = 1125 μm
 The approximate length maybe calculated using
the formula:
Approximate length of object = fraction X diameter of field

To determine the magnification of a drawing.
1. You need the actual size of the object drawn
and the actual size of the drawing.
2. Magnification of the drawing can be calculated
using the formula:
Magnification of drawing = drawing size
object size

3. For example if your object has an actual length
of 1115 μm, and your drawing of that object has
a length of 5 cm, then you ,can calculate
magnification of drawing as follows:
First the 5cm must be converted into μm that is
5 X 10 000 = 50 000 μm
Then:
Magnification of drawing = drawing size
object size
= 50 000/ 1115
= 45 μm

To determine the actual size of the object whose
image or micrograph is viewed using a scale line.
1. Determine what the scale line measures.
2. Assume it represents 1 μm.
3. Measure the scale line given in the drawing or
micrograph. ( lets say its 15mm)
4. Measure the length of the image in ;the drawing
or micrograph. ( lets say its 50mm)
5. Now we can use the following formula

= 50mm X 1 μm
15mm
= 3.3 μm
Actual size = measured length of object (mm) X length of scale line (μm)
measured length of scale line (mm))

 Macroscopic: refers to organisms that are visible
to the naked eye.
 Microscopic: refers to organisms that are so small
that they are not visible to the naked.
 Field of view: is the circle of light that you see
when looking through the eyepiece

1. The platform on which the slide sits is called
the…
A. Base
B. Stage
C. Condenser
D. diaphragm

2. Opening that controls the amount of light
entering the microscope
A. Base
B. Stage
C. Condenser
D. diaphragm

3. It concentrates light through the slide and
specimen
A. Base
B. Stage
C. Condenser
D. diaphragm

4. The combination of lens to magnify the image
from objectives and specimen…
A. Eyepiece
B. Body tube
C. Illuminator
D. Mirror

5. It supports and links the optical parts.
A. Eyepiece
B. Body tube
C. Illuminator
D. Mirror

6. Provides support for the microscope
A. Base
B. Stage
C. Condenser
D. diaphragm

7. Provides electrical light when switched on.
A. Eyepiece
B. Body tube
C. Illuminator
D. Mirror

8. Provides a source of natural light.
A. Eyepiece
B. Body tube
C. Illuminator
D. Mirror

9. Attachment of objectives.
A. Nose piece
B. Mechanical stage
C. Stage clips
D. Fine adjustment screw

10. Holds the slide in position on stage.
A. Nose piece
B. Mechanical stage
C. Stage clips
D. Fine adjustment screw

11. Allows for easy movement of slide
A. Nose piece
B. Mechanical stage
C. Stage clips
D. Fine adjustment screw

12. The picture below shows the microscope used by…
A. Robert Hooke
B. Van Leeuwenhoek
C. Oken
D. Lamarck

13. The scientist who viewed cork cells under a
simple microscope.
A. Robert Hooke
B. Van Leeuwenhoek
C. Oken
D. Lamarck

14. The scientist that observed and described
single celled organisms.
A. Robert Hooke
B. Van Leeuwenhoek
C. Oken
D. Lamarck

15. The electron microscope was invented by…
A. Robert Hooke
B. Van Leeuwenhoek
C. Zworykin
D. Lamarck

16. Calculate the magnification power of a
microscope if you use the medium power
objective and the 15X eyepiece.
A. 150X
B. 75X
C. 25X
D. 20X

17. Calculate the length of an object if it covers ½
of the field of view, assume that the diameter
of the field of view is 4500μm…
A. 2250 μm
B. 2000 μm
C. 4500 μm
D. None of the above

18. Calculate the magnification of a drawing you
have done if your drawing of the organism is
2500 μm and your drawing of it is 7 cm long.
A. 2507 μm
B. 28X
C. 0,0028
D. 28 μm

19. If you wanted to scan and view the surfaces of
objects, you must use the…
A. Electron microscope
B. SEM
C. TEM
D. Light microscope

20. If you wanted to see the inside of objects you
would use the…
A. Electron microscope
B. SEM
C. TEM
D. Light microscope

1. B
2. D
3. C
4. A
5. B
6. A
7. C
8. D
9. A
10. C
11. B
12. B
13. A
14. B
15. C
16. A
17. A
18. B
19. B
20. C