Microscopy
MICROSCOPE
A microscope is an instrument used to see objects
that are too small for the naked eye.
The science of investigating small objects using
such an instrument is called microscopy.
Microscopic means invisible to the eye unless
aided by a microscope.
Parts of the
light
microscope
Objective lenses
HP objective lens is
close to slide
Total magnification:
Magnification = Objective lens X Eyepiece lens
e.g. What is the total
magnification if the objective lens
is twenty times (X20) and the
eyepiece lens five times (X5)?
Magnification = 20 X 5 = X100
As magnification increases, detail
increases but:
Onion cell 40x
less of the cell is seen
Onion cell 100x
Onion cell 400x
Caring for the microscope:
1. Do not let any liquids to come in contact
with the microscope.
2. Always store the microscope inside a box
after use.
3. Return the objective lens onto low power
after use.
4. Carry the microscope by the arm.
5. Use a soft clean tissue to wipe the lenses
Coverslips
Microscope
slides
Fig. 2 Preparing
a slide as a wet
mount.
Use of stains:
 some parts of a plant cell can be clearly seen
when the cell is mounted in water
 E.g. an Elodea leaf cell:
 cell wall
are seen
 several chloroplasts
 other cell structures which are not so
obvious can often be shown up more clearly
by the addition of dyes called STAINS
IODINE SOLUTION
To stain plant cells
METHYLENE BLUE
To stain animal cells
3
2
1
One of the fleshy scale
leaves is removed.
An onion is cut
into quarters.
Snapping leaf backwards
exposes the epidermis.
5
4
6
Epidermis is placed on
slide & covered with 2-3
drops of distilled water .
Coverslip is lowered.
A thin inner layer of
epidermis is peeled
off.
7
A drop of stain is put at
one end of slide.
Stain is drawn over
specimen using a small
piece of filter paper.
Questions
1. A student prepared a microscope slide of onion
cells using water.
Diagram A shows how the cells looked when
first seen with the microscope.
Diagram B shows their appearance after the
addition of another liquid.
What name is given to a liquid used to make
cell structures easier to see?
Stain
2. The drawing shows the appearance of a
prepared slide.
What causes the ring shapes? (1)
Air bubbles trapped beneath the coverslip.
3. This diagram shows the main parts of a
typical light microscope.
a) How is a glass slide held in position on the
stage?
By the clips.
b) Why must the specimen on the slide be in
the center of the hole in the stage?
To allow light pass through the specimen.
c) Why does the nosepiece rotate?
To clip in position the required objective lens.
d) What is the mirror for?
To reflect light onto the specimen.
e) How can you control the amount of light
coming through the microscope?
By moving the diaphragm.
f) Explain how you would use the microscope
to look at a specimen under the low power.
1. Clipping slide by clips.
2. Placing the low power objective in position.
3. Moving the tube downwards while looking
from the side until objective lens is close to
the slide.
4. Using the coarse adjustment
knob, the tube is racked
upwards until image is focused.
g) If you had a specimen in focus under the low
power, how would you go on to look at it
under high power?
By using the fine adjustment knob.
h) Why should you never rack downwards with
the coarse focusing knob while you are
looking down the microscope?
Not to break the slide.
i) If the magnifying power of the eyepiece lens
is ten times (X10), and that of the low power
objective lens is four times (X4), what is the
total magnification of a specimen under low
power?
10 x 4 = x40