Microscopes allow observation of objects too small to be seen with the naked eye. They were instrumental in discovering that cells are the basic unit of life and identifying disease-causing microorganisms. A microscope has a stage to hold slides, a light source, lenses that refract light to magnify the specimen, objective lenses that can be changed for different magnifications, and eyepieces. Specimens must be thin to view under the microscope and are placed on slides with a cover slip. Temporary slides can be made from pond water or cheek cells, while permanent slides include plant stems.

1. How to use a Microscope

2.  To see things that are too small to see with
our eyes or even with a hand lens
 Microscopes enabled scientists to
understand that cells are self contained
units
 They were able to identify bacteria and
other disease causing organisms
Why do we use microscopes?

3.  To look at something under a
microscope it needs to be very thin
 This is because light needs to pass
through the specimen
 The specimen is first placed on a
glass slide – which is obviously see-
through
 The specimen is covered in a cover
slip – this is a really thin piece of
glass
 We will make our own slides soon
 you can also buy permanent slides
Slides

4. This is a permanent slide of a plant
stem
Note the
individual cells
It is being looked
at under a fairly
low power – a
higher power
would show
fewer cells but in
greater detail

5. This is a temporary slide of a drop of
pond water
There are lots
of living
organisms we
can only see
under a
microscope

6. What a Microscope looks like
This is the
diagram in
your notes.
Highlight the
important
labels and note
the functions
of each part as
you go through
them

7. Stage: the slide
goes onto the stage
and is held in place
with clips.
Don’t clip a slide in
place until you have
found an area to
look at

8. All microscopes
need a source of
light.
Some have a bulb
but the ones you
will use have a
mirror.
You need to reflect
light from a bulb or
a window so it goes
up through the
specimen on the
stage

9. There are two
lenses that
will refract
light to make
the image
much larger
that the
actual
specimen
They magnify
the image
The eye piece
magnifies by
x10
This is what
you look
through

10. The objective lenses are
attached to a rotating disc so
they can be changed
Always start with the lowest
power-which is the shortest.
This usually magnifies x10
So with the eyepiece that is:
x(10x10) or x100
Once you have focused using
the low power move the
higher power into place- this is
the longer objective lens

11. We focus on the
specimen using the
focusing knob
Most microscopes have
two focusing knobs:
The big one is the course
focus knob that you use
to focus on low power
The small one is the fine
focus knob, used only
with the higher power
objective lens

12. Take a look at this
picture that shows
how light is refracted.
You will see when you
use a microscope that
the image is upside
down and back to
front:
when you move the
slide up the image will
move down – you will
get used to it!

13. Test yourself

14. Read through the notes on how to
use a microscope
Be aware of the parts of the
microscope being referred to

15. Making a slide
 In the next lesson we will make slides and look
at them
 To see cells clearly we stain them with
chemicals
 So there are a few steps that you should be
familiar with before you try it yourself.

16.  The trick here is to peal off a small piece of
epidermis – your teacher will show you how to
do this in the lesson
 The epidermis is placed carefully on a slide. Be
careful not to fold it
 We then place a drop of water on top to stop
the cells drying out
Looking at an Onion Epidermal Cells

17.  Now we need a cover slip – the trick here is
to lower the cover slip so there are no air
bubbles
 Blotting paper removes excess water

18. Staining by Irrigation
You will stain your onion
epidermis with Iodine
solution
This is done by placing a
drop of iodine solution next
to the cover slip
and drawing it through with
blotting paper:

19. Looking at Cheek cells
Scrape the inside of your cheek very
gently with the back of your thumb
nail
Now rub that onto a slide
Cover in a drop of water then place a
cover slip on top without making any
air bubbles!

20.  Cheek cells are stained by irrigating with
Methylene Blue
 Don’t get this on your skin!
 Cheek cells are about 12m in diameter
 That is about 0.012mm
 They will have to be magnified to see them