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B1 page 11-13 (microscopes (light microscopes (use light and lenses to…
B1 page 11-13
microscopes
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the microscopy techniques we can use have developed over the years as technology and knowledge have improved
light microscopes
use light and lenses to form an image of a specimen and magnify it. they let us see individual cells and large subcellular structures, like nuclei.
electron microscopes
use electrons instead of light to form an image. they have a lot higher magnification and resolution than light microscopes. they let us see much smaller things in more detail for example the internal structure of mitochondria and chloroplasts. they even let us see tinier things like ribosomes and plasmids
resolution is the ability to distinguish between two points, so a higher resolution gives a sharper image
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standard form
because microscopes can see such tiny objects, sometimes its useful to write numbers in standard form
it is where you change a very big or small numbers with lots of zeros into something more manageable
to make a number standard form you need to move the decimal point left or right. the number of places the decimal point moves is then represented by a power of 10 (this is positive if the number is moved to the left and negative if it is moved to the right)
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microscopy practical
if you want to look at a specimen ( e.g. plant or animal cells) under a light microscope, you need to put it on a microscope slide first. a slide is a strip of glass or plastic onto which the specimen is mounted. here is how to prepare a slide to view onion cells
using the tweezers, place the epidermal tissue into the water on the slide
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
cut up an onion and separate it out into layers. use tweezers to peel off some epidermal tissue from the bottom of one of the layers
place a cover slip ( a square of thin, transparent plastic or glass) 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.
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drawing observations
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make sure your drawing takes up at least half of the space available and that it is drawn with clear, unbroken lines
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remember to include a title of what you were observing and write sown the magnification that it was observed under
label the important features of your drawing (e.g. nucleus, chloroplasts) using straight, uncrossed lines
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magnification
image size / real size (these should be in the same units meaning they may need to be converted before being calculated)
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