Bacterial Cells, Microscopy, and Staining Techniques

Flashcards about bacterial cells, microscopy, and staining techniques based on lecture notes.

Why is the microscope one of the most important tools for studying microorganisms?

Because microorganisms are very small and cannot be seen without it.

What type of microscope is typically found in a microbiology lab?

The light microscope.

What are the two sets of magnifying lenses in a compound light microscope?

Ocular lens (eyepiece) and objective lenses.

What is the function of the condenser in a microscope?

To focus the light that comes from the illuminator onto the specimen.

What does the iris diaphragm control in a microscope?

Controls the amount of light that goes up into the specimen.

When do you use the coarse focus knob on a microscope?

When you are on low power (10x) to get your image into focus.

When do you use the fine focus knob on a microscope?

On the 40x and 100x objective lenses only.

What is total magnification (TM)?

The power of the objective lens multiplied by the power of the ocular lens.

What objective lens is also referred to as the oil immersion lens?

The 100x objective lens.

What is resolving power (resolution) on a microscope?

The ability of the microscope or lens to distinguish two objects that are very close together.

What is the purpose of immersion oil when using the 100x objective lens?

To increase the resolution by preventing the bending of light rays as they pass from the slide to the objective lens.

What does contrast refer to in microscopy?

How easy it is to see an organism against the background.

How can you increase the contrast in light microscopy?

By staining the bacteria or using different types of microscopy (phase contrast or dark field).

What is the maximum magnification limit for light microscopes?

A thousand times (1000x).

What types of specimens is bright field microscopy usually used to view?

Colored or stained specimens.

What type of specimens is dark field microscopy usually used to view?

Live specimens that are not colored or that are transparent.

What cellular feature is face contrast microscopy mainly used to look at?

Internal structures of live organisms.

What type of light does fluorescence microscopy use?

UV light.

What does SEM stand for regarding electron microscopes?

Scanning Electron Microscope.

What does TEM stand for regarding electron microscopes?

Transmission Electron Microscope.

Which type of electron microscope is used to view the surface of cells?

Scanning Electron Microscope (SEM).

Which type of electron microscope is used to look at the insides of cells?

Transmission Electron Microscope (TEM).

What is a smear?

A thin layer of bacteria that is put onto the surface of a slide.

How is a bacterial smear fixed to a slide?

Using heat.

How do basic dyes stain bacteria?

They carry a positively charged cation that binds to the slightly negatively charged bacterial cell.

How do acidic dyes stain bacteria?

They are negatively charged and stain the background, making the bacteria pop out.

What is a simple stain?

It only uses one stain to stain the cell or the background.

What is a differential stain?

A more complex staining procedure that uses a series of reagents and stains to distinguish between different types of bacteria.

Name two examples of differential stains.

Gram stain and acid-fast stain.

What outcome does the Gram stain provide?

Separates bacteria into two groups: gram-positive (purple) and gram-negative (pink/red), based on cell wall structure.

What is the first step in the Gram staining procedure?

Application of crystal violet, a basic dye, that stains all cells purple.

What is the function of iodine in the Gram staining procedure?

It acts as a mordant, binding to the crystal violet to form a complex that is harder to wash out of the cell.

What is the purpose of the alcohol wash (decolorizer) in the Gram staining procedure?

To remove the dye from the gram-negative cells while the gram-positive cells retain the purple dye.

What is the counterstain used in the Gram staining procedure?

Safranin, a red dye.

What color are gram-positive cells after the Gram staining procedure?

Purple.

What color are gram-negative cells after the Gram staining procedure?

Pink to red.

What is specifically detected using the acid fast stain?

Members of the genus Mycobacterium.

What is the primary dye used in the acid fast stain?

Carbofusion, a red dye.

What is the decolorizer used in the acid fast stain?

Acid alcohol.

What is the counterstain used in the acid fast stain?

Methylene blue, to stain non-acid-fast bacteria blue.

In the acid fast stain, what color are acid fast cells?

Red. Those cells are able to withstand the acid wash so that the dye primary dye is not removed by the acid.

What color are non-acid-fast cells in the acid-fast stain?

Blue

Why is a capsule stain used?

Gel-like structure that surrounds the bacterial cell is poorly stained. Stain only the background to better see the surrounding capsule.

What is special about performing an endospore stain?

It uses heat in the process. Because the endospore is resistant, a primary dye such as malachite green drives stain into cell.

Which stain should be used to determine motility and number of flagella?

Flagella stain.

What are the two most common shapes of bacteria?

Coccus (spherical) and rod (cylindrical).

What is pleomorphic bacteria?

Bacteria that display many different shapes.

What is used to determine the shape of the bacteria cell?

The cell wall.

What is morphology?

The shape of the bacterial cell.

What is binary fission?

It is how cells divide; a cell gets bigger and splits into two.

What are diplococci?

Pairs of spherical bacteria attached to each other.

What are streptococci?

Chains of spherical cells.

What are tetrads?

Packets of four cells.

What are staphylococci?

Grape like clusters of spherical cells.

What does it mean for a cell wall to be pleomorphic?

Bacteria without a rigid cell wall form different shapes.

Name 5 structures that every bacteria has.

Ribosome, cytoplasm, chromosome, cell wall, and plasma membrane