MCB 2010 Module 2 Assignment

Why must fresh cells be used for the Gram stain?

As cells age, they may not stain correctly

If you viewed the slide microscopically after the crystal violet step, Gram-positive cells would appear _________blank in color while Gram-negative cells would appear _________blank in color.

purple; purple

Why is Gram's iodine added to the slide?

It forms complexes with the crystal violet, decreasing its solubility.

If you viewed the slide microscopically after the ethanol/acetone step, Gram-positive cells would appear _________ while Gram-negative cells would appear _________

purple; colorless

Gram-positive bacteria retain the crystal violet-iodine complexes because the ethanol/acetone

dehydrates the thick peptidoglycan cell wall, making it impermeable

During the Gram stain procedure, bacteria can first be differentiated from each other after the application of _________

decolorizer

If the Gram's iodine step was skipped in this technique, what would likely be seen under the microscope, providing all other steps were performed correctly?

Most cells would appear red/pink

All bacteria can be classified as either Gram-positive or Gram-negative

False

The presence of flagella can be determined by a Gram stain.

False

Rod-shaped bacteria

can be either Gram-positive or Gram-negative.

After Gram's iodine is added to the slide, what color do cells appear?

All cells appear purple in color.

The thinner peptidoglycan layer of Gram-positive bacteria allows the crystal violet-iodine complex to leave the cell.

False

Which of the following cell arrangements is described CORRECTLY?

Diplococcus - pairs of spherical cells

Mycoplasma pneumoniae lacks a cell wall and is a pleomorphic.

True

Which of the following bacterial groups is described CORRECTLY?

Spirochetes – move by axial fibrils

Which of the following bacterial genera is NOT described correctly?

Corynebacterium – spherical

The target of penicillin in bacterial cells is ______.

the cell wall

Match the descriptions given below to either the capsule or slime layer. Only six labels are used.

this one

Which of the following ways in which molecules move across a membrane does not require energy?

this one

Small amounts of LPS alert the body to invasion by Gram-negative bacteria, while large amounts of LPS may cause shock and death.

True

Identify the differential staining method that is most important in the diagnosis of tuberculosis, caused by Mycobacterium tuberculosis.

Acid-fast stain

Which of the following can affect the resolution of a bright-field microscope?

• wavelength of light

• type of specimen

• quality of lenses

• type of specimen and magnification

Microbes from the domain Archaea have cell walls containing peptidoglycan.

True

Match the staining technique to the appropriate example.

this one

In a capsule stain,

this one

Which of the following about simple and differential staining is CORRECT?

Simple stains use a single color while a differential stain uses more than one color to highlight differences between certain groups of cells.

Which of the following bacterial structures is most directly linked to chemotaxis?

Flagella

Match the types of cytoskeletal elements with their correct function.

Mostly responsible for mechanical support and helps the cell resist physical stress.

Intermediate filament

Match the types of cytoskeletal elements with their correct function.

Typically functions to allow the cell cytoplasm to move.

Actin filament

Match the types of cytoskeletal elements with their correct function.

Involved in the movement of chromosomes during cell division

Microtubule