microscopes let us see things we can't see with the
naked eye. The microscopy techniques have
developed over the years as technology and
knowledge have imporved.
Light microscopes use light
and lenses to form an image
of a specimen and magnify it.
They let us see individual
subcellular structures
Electron microscopes use electrons instead of light to
form an image. They have higher magnification than light
microscopes
They also have a higher
resolution to distinguish
between two points, so a
higher resolution gives a
sharperimage.
electron microscope let us see much smaller things in
more detail
You need to prepare your slide
If you want to look at a
specimen under a light
microscope, you need to put it
on a microscope slide first.
A slide is a strip of clear glass or plastic onto
which the specimen is mouted.
Here's how to prepare a slide to view
onion cells:
1. Add a drop of water to the middle of a clean slide
2. cut up an onion and seperate it out into layers. use
tweezers to pell off some epidemal tissue from the
bottom of one of the layers.
3. Using tweezers. place the epidermal tissue into the water on the slide.
4. Add a drop of iodine solution, iodine solution is a stain.
Stains are used to highlight objects in a cell by adding colour to
them.
5. Place a cover strip on top. To do this, stand the cover slip upright on the slide, next to the water
droplet. Then carefully tilt and lower it so it covers the specimen. try not to get any air bubbles - they
will obstruct the view of the specimen.
Use a light microscope to look at your slide
To look at the prepared slides, you need to know how to use a
light microscope
1. clip the slide you've prepared onto the stage
2. Select the lowest - powered objective lens
3. use the coarse adjustment knob to move the stage up to
just below the objective lens.
4. Look down the eyepiece. use the coarse adjustment knob to move the stage
downwards until the image is roughly in focus.
5. Adjust the focus with the fine adjustment knob, until
you get a clear image of what's on the slide
6. If you need to see the slide with greater magnification,
swap to a higher - powered objective lens and refocus
Draw your observations neatly with a pencil
make sure your drawing takes
up at least half of the space
available and that it's draw
with clear, unbroken lines
the drawing shouldn't include any colouring or shading
if you're drawing cells, the subcellular structures should be
drawn in proportion
remember to include a title of what you
were observing and write down the
magnification that it was observed under.
label the important features, using straight, clear
lines