How to use a Microscope

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?

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

This is a permanent slide of a plant stem

Note the individual cellsIt is being looked at under a fairly low power – a higher power would show fewer cells but in greater detail

This is a temporary slide of a drop of pond water

There are lots of living organisms we can only see under a microscope

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

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

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

There are two lenses that will refract light to make the image much larger that the actual specimenThey magnify the image

The eye piece magnifies by x10This is what you look through

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 x10So 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

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

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!

Test yourself

Read through the notes on how to use a microscope

Be aware of the parts of the microscope being referred to

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.

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

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

Staining by IrrigationYou 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:

Looking at Cheek cellsScrape the inside of your cheek very gently with the back of your thumb nail

Now rub that onto a slideCover in a drop of water then place a cover slip on top without making any air bubbles!

Cheek cells are stained by irrigating with Methylene Blue

Don’t get this on your skin!

Cheek cells are about 12m in diameterThat is about 0.012mmThey will have to be magnified to see themYou will learn how to calculate

magnification