[OLD] Cells - Microscopes Flashcards
What is magnification?
The number of times bigger an image is than the object
What is resolution?
The ability to see two close together objects as separate objects.
(The detail that can be seen, not clarity)
Why is staining done?
Done to improve congrats in a preparation to see specific organelles, cell types or stages of mitosis of the cells
Maximum magnification of a light microscope
1500x
Max resolution of a light microscope
200nm
Characteristics of light microscopes
Can view live specimens in colour light focused by glass lenses no vacuum easy slide preparation - unlikely to distort sample / introduce artefacts. Stains added to improve contrast
Maximum magnification of electron microscopes
500,000x
Maximum resolution of electron microscopes
0.1 - 0.2nm
Characteristic of electron microscopes
Can only view dead specimens
In black and white
Electron beam focused by electromagnets
Sample must be in a vacuum
Complex slide preparation - more likely to distort sample / introduce artefacts
Sample stained by being covered in electron dense heavy metal compounds e.g gold
How do transmission electron microscopes work?
Electrons fired at a very thin section of sample Electron that pass through sample are detected on a screen behind the sample 2D image (very high magnification and resolution)
How do scanning electron microscopes work?
Electrons bounce off samples surface and hit detector
Allows a 3D image of (e.g) cell surfaces to be seen (slightly lower magnification and resolution)
which organelles can and can’t you see through a light microscope?
you can’t see ribosome, endoplasmic reticulum or lysosomes. you may be able to make out the mitochondria but not in perfect detail. you can see the nucleus
Pros and cons of TEMs
they are good because they give high resolution images so you see the internal structure of organelles like chloroplasts
however they can only be used on thin specimens
Pros and cons of SEMs
They are good because they can be used on thick specimens. However they give lower resolution images than TEMs
How do you prepare a temporary mount of a specimen on a slide?
1) pipettes a small drop of water onto the slide. use tweezers to place a thin section of your specimen on top of the water drop.
2) add a drop of stain to highlight objects in a cell.
3) add the cover slip by standing the 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 under it ( it will obstruct your view of the specimen)
