How to use a microscope

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 m agnified to see them