c/o to the owner

1. Focus specimens
using the
compound
microscope
PREPARED BY: TYPE YOUR NAME HERE

2. Focus specimens using
the compound
microscope
LEARNING
COMPETENCY

3. Why do we use microscopes?
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

4. Slides
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

5. 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

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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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!

14. Test yourself

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

16. 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.

17. Looking at an Onion Epidermal Cells
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

18. 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

19. 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:

20. 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!

22. 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