microscopy

what is the purpose of a microscope?

to magnify objects so we can see small structures, such as cells.

what is the difference between a light microscope and an electron microscope?

electron microscopes have higher magnification and higher resolution, so they show more detail

what does magnification mean?

how many times bigger the image is than the real object.

what is the formula for magnification?

magnification = image size ÷ real size.

how do you convert millimetres (mm) into micrometres (μm)?

multiply by 1000

write 0.0025 mm in standard form.

2.5 × 10 -3 mm

how do you prepare an onion-cell slide?

1. add a drop of water to a clean slide.

2. peel a thin layer of onion epidermis using tweezers.

3. place the tissue in the water.

4. add a drop of iodine solution.

5. carefully place a coverslip on top.

why is iodine solution added to the slide?

it stains the cells, making their structures easier to see.

why should you avoid air bubbles under the coverslip?

air bubbles can obstruct the view of the cells.

what is resolution?

the ability to distinguish two close points as separate.

using a light microscope

1. clip the slide onto the stage

2. select the objective lens with the lowest magnification

3. use the coarse adjustment knob to move the stage up to just below the objective lens

4. look down at the eyepiece move the stage downwards until the image is roughly in focus

5. move the fine adjustment knob until you get a clear image of what's on the slide

6. for a bigger image, use objective lens with a higher magnification and refocus