BIOL 255 Ch. 2 - Microscopy

Explain why microscopy is a major tool used by microbiologists

Allows scientists to see microbiologists that are smaller than the naked eye can see, and allows them to see their internal characteristics and details

How light interacts with objects and liquid media

• Reflection – light bounces off the object without passing through Refraction – Light bends as it passes through an object

• Interference – multiple light waves interact and reinforce or cancel each other

• Diffraction – light spreads or. Bends when it hits an edge or fine details

What is refractive index and how does it influence resolution

• Refractive index: measure of how much a substance slows the speed of light

• The higher the refractive index, the higher the resolution

Define magnification and resolution

• Magnification: enlarging the image of the original object

• Resolution: Ability to distinguish fine details

How does wavelength relate to resolution

Shorter wavelength = greater resolution

What is the function of immersion oil

At high magnification (100x objective lens) resolution decreases as the light refracts, immersion oil focuses the light and increases the resolution

How is the total microscope’s magnification calculated

total magnification = (objective lens) x (ocular lens)

What can we see in a light microscope

Live specimens, inner cell structures, 2D images, biofilms

What can we see in an electron microscope

Subcellular structures, 3D detailed surfaces

What is the importance of fixation

Increases visibility of specimen, accentuates morphological features, preserves specimens

What are the chemical characteristics of a stain

• Positive stains – dyes the cell wall

• Negative stains – dyes the background

• Imparts color, positively or negatively charged portion

What is the difference between simple and differential staining

• Simple – single dye, all organisms are the same color even if different types of organisms

• Differential staining – distinguishes organisms based on interactions with multiple stains

• EX: Gram positive cell wall = purple; gram negative = pink

What cellular structures do differential staining allow us to observe

Flagella, capsule, endospore

What is the difference between scanning and transmission electron microscopes

• Scanning – surface of specimen is viewed

• Transmission – view interior structures of the specimen