Lab Exam 1 Study Guide

These flashcards cover important concepts regarding microscopy, microbial characteristics, staining techniques, and aseptic practices necessary for the Lab Exam.

What are the main differences between a compound light microscope and an electron microscope?

A compound light microscope uses light for illumination and can view living specimens, while an electron microscope uses beams of electrons, providing higher resolution, and is used for non-living specimens.

What types of specimens are best viewed with a compound light microscope?

Living cells, microorganisms, and thin sections of tissue.

What types of specimens are best viewed with an electron microscope?

Detailed structures of cells, viruses, and organelles.

What are the basic parts of a compound microscope?

Eyepiece, objective lenses, stage, light source, and focus knobs.

How do you calculate the total magnification of a microscope?

Multiply the magnification of the eyepiece by the magnification of the objective lens being used.

What does 'parfocal' mean in microscopy?

The ability of a microscope to stay in focus when switching between different objectives.

What is resolution in microscopy?

The ability to distinguish two close objects as separate.

What is resolving power?

A measure of the clarity of an image under a microscope.

What is numerical aperture in microscopy?

A function that describes the range of angles over which the system can accept or emit light.

How do you determine the numerical aperture of a lens?

It is calculated using the formula NA = n × sin(θ), where 'n' is the refractive index and 'θ' is the half-angle of the maximum cone of light.

Why is oil immersion important for resolution?

It reduces light refraction, allowing more light to enter the lens, resulting in higher resolution.

How can you distinguish between eukaryotic and prokaryotic microorganisms with a compound microscope?

Eukaryotic cells have a defined nucleus and organelles, while prokaryotic cells lack a nucleus and are generally smaller.

What are the shapes of bacteria?

Coccus (spherical), bacillus (rod-shaped), spiral, and vibrio (comma-shaped).

What are the characteristics of protozoa?

Single-celled eukaryotes, heterotrophic, motile, and can reproduce sexually or asexually.

What are the four categories of protozoa based on motility?

Flagellates, ciliates, amoeboids, and sporozoans.

Give examples of each category of protozoa based on motility.

Flagellates ( Giardia), ciliates ( Paramecium), amoeboids (Amoeba), sporozoans ( Plasmodium).

What are the characteristics of green algae?

Photosynthetic, unicellular or multicellular, contain chlorophyll, green in color

What are the characteristics of cyanobacteria?

Photosynthetic, prokaryotic, have choraphyll,no chroloplasts,blue-green color.

What are the characteristics of fungi?

Eukaryotic, heterotrophic, cell wall composed of chitin, and reproduce by spores.

What is Brownian movement?

The random movement and vibrations due to collision with fast-moving molecules. (not real mobility)

What is a hay infusion?

An environment created by steeping hay in water to cultivate microorganisms.

Why is it necessary to make a hay infusion?

To create a nutrient-rich environment for the growth of microorganisms.

What are the two different types of wet preparations?

Wet mounts and hanging drops.

What are the advantages of wet preparations?

observe live cells, natrual mobility, morpholgy

What are the disadvantages of wet preparations?

Short observation time due to evaporation and difficulty maintaining focus.

How do you distinguish between Brownian movement and true motility?

Brownian movement is passive motion due to molecular collisions, while true motility involves purposeful movement by the organism.

How do you prepare a wet-mount slide?

Place a drop of liquid on a slide, gently lower a coverslip at an angle to avoid air bubbles.

What are important points to remember when practicing aseptic technique?

Keep work area clean, sterilize tools before use, avoid contamination, and work swiftly.

Define culture medium.

A nutrient solution used to grow microorganisms.

What does 'fastidious' mean in microbiology?

Microorganisms that have complex nutrient requirements.

What is inoculation in microbiology?

The introduction of microorganisms into a culture medium.

What is inoculum?

The sample of microorganisms introduced into a culture medium.

What is aseptic technique?

Methods used to prevent contamination during microbiological procedures.

What are the growth patterns of bacteria in broth cultures?

Pellicle (surface growth), sediment (growth at bottom), turbidity (cloudy), and flocculent (clumps)

What is the quadrant streak plate method of isolation?

A technique used to isolate individual colonies from a mixed culture.

What is the purpose of the streak plate method?

issolate pure colonies from mixed culture

What are some characteristics of a bacterial colony that can provide clues to its identification?

Color, shape, size, margin, and elevation.

What kinds of controls are used to determine that media was prepared correctly?

Positive and negative controls with known microorganisms.

Why is agar a good solidification agent for microbiological media?

It remains solid at incubation temperatures and is not digested by most microbes

How is media sterilized?

Commonly by autoclaving, which uses steam under pressure.

Define chromophore.

The part of a dye that gives it color.

What is simple staining in microbiology?

Using a single dye to highlight basic structures of microbes.

What is negative (indirect) staining?

A staining technique that stains the background, not the cell itself

Why are specimens fixed before staining?

To kill and adhere the microorganisms to the slide.

What is the difference between an acidic and basic dye?

Acidic dyes have a negative charge and stain background; basic dyes have a positive charge and stain the cells.

What charge does a bacterial cell have?

A negative charge.

When would you use a dye with the same charge as the specimen?

in a negative staining procedure

When would you use a dye with the opposite charge?

in a positive staining procedure

What are the four basic reagents used in differential staining?

a primary stain, a mordant, a decolorizing agent, and a counterstain

Define differential staining.

using multiple dyes to distinguish different groups

What is the basic process of acid-fast staining?

primary stain- carbolfuchsin

mordant- heat

decolorizer- acid alcohol

counterstain- methylene blue

What genus of clinically relevant bacteria are acid-fast?

Mycobacterium.

What component of the cell wall of acid-fast bacteria makes it impermeable?

Mycolic acid.

After acid-fast staining, acid-fast bacteria stain what color?

Pink.

Why is the Gram stain an important procedure in the clinical lab?

It helps identify bacteria and guides treatment options.

What are the structural differences between gram-positive and gram-negative bacteria?

Gram positive- bacteria have a thick peptidoglycan layer; retain crystal violet

gram negative- have a thin peptidoglycan layer and an outer membrane. lose crystal violet

Describe the Gram staining procedure.

primary stain with crystal violet,

mordant with iodine,

decolorize with alcohol,

counterstaining with safranin.

What color do gram-positive bacteria stain?

Purple.

What color do gram-negative bacteria stain?

Pink.

What is the most critical step of the Gram stain procedure?

The decolorization step.

What type of cultures should be used for Gram staining?

Young cultures (18-24 hours old).

What are the consequences if specific steps of the Gram stain procedure are skipped?

Misidentification of bacteria could occur.

primary stain- all cells will appear pink

mordant- the cells will wash away

decolorize- all cells stay purple

counterstain- gram negative cells stay clear