• increase in the size of an image
• calculated by: strength of the objective lens (100x) x strength of the ocular lense (almost always 10x)
• a 1 μm cell (under 1000x) appears 1 mm

• the ability to differentiate two points from one another 
• determined by wavelength of light and NA (numerical aperature) of the lense
• for a light microscope: best resolution is 200 nm, or 0.2 μm

light microscope

(advantages and disadvantages)

• simple, doesn't require a computer
• inexpensive
• includes bright field microscopes 
• does not show living cells
• needs a stain to view the cell, which kills the cell

• large and expensive
• complex
• magnification = 1,000,000x
• resolution = 2.0 nm (same as light microscope) 
• no heavy metal stains needed
• can look at live cells
• useful for looking at surface topology

• detects a change in the light waves that pass through the cell
• compares this to those light waves that do not pass through 

• all of the light gets blocked, and does not enter the objective lens unless a cell enters the view
• image appears as a refraction of light
• simple and effective
• sometimes it's too dark, and the image needs to be further illuminated, which can damage the sample
• can view living cells 

• allows you to look at live cells
• same resolution and magnifications limits
• more expensive and technically complex
• the image is the light that is absorbed by the fluorescence in the cell 

• magnification = 100,000x
• resolution = 0.0002 nm
• heavy metals, like iron, must STAIN the cells in order to be seen, killing the cell
• cannot view living cells because they don't block the electron beam

• just makes the sample visible, the color doesn't matter
• does not determine different types of cells 
• only used to view the cell

• is used to determine the types of cells
• one type stains one color, while another type stains a different color
• Gram Stains are the most common type

staining process

(steps)

1. crystal violet (stains all cells purple)
2. iodine (precipitates)
3. Ethanol (decolorizes)
4. Safronin/Basic Fusion (counter stains)

• cells with a very thin peptidoglycan cell wall, which allows the iodine precipitates to wash out of the cell 
• stains pink 
• has Lipid A in the outer membrane 
• has channels (called porins) in the outer membrane 

• cells have a thick peptidoglycan cell wall, traps iodine precipitates
• stains purple