2.1/3 Microscopy Flashcards
Why is staining used
To increase the contrast between different components of the cell
This is because most images have a low contrast, as most cells do not absorb a lot of light
What is the staining process
Sample must be air dried
Then heat fixed by passing through a flame after the stain has been added
Positively charged stains
Are violet and blue
Which are attracted to negatively charged materials in the cytoplasm
negatively charged stain
Dyes of nigrosin or congo red are negative so are repelled negatively by N- cystol.
These dyes stay out is the cell which makes the cell stand out against the stained background
Differential staining
Can distinguish between 2 types of organism.
Can also differentiate between different organelles within a sample tissue.
gram stain technique
Used to separate bacteria into 2 groups
Crystal violet + iodine is added to the slide
Slide is then washed with alcohol
What will happen is the bacteria is negative using the gram stain technique
Negative bacteria will lose the stain
They are then stained with saffron dye, called a counter stain which will appear red
Resolution
The shortest distance between 2 objects where they can be clearly identified as 2 separate objects
Which microscope produces 3D images
Scanning
How transmission microscopes work
Beam of electrons is transmitted through a specimen to produce an image
Best resolution with the resolving power 0.5nm
How scanning electron microscope works
Beam of electrons sent across the surface of a specimen and the reflected electrons are collected
Resolving power from 3-10nm
Differences between light and electron microscope
Price , size Complex sample preparation- electron Preparation often leads to distortion- electron Vacuum required- electron Light - 2000 magnification , electron- 500,000 magnification Resolving power light - 200nm Resolving power scanning 3-10nm Resolving power transmission 0.5nm Light- specimens can be alive or dead Electron- specimens are dead
