Chapter 3 Microscopy & Cell Structure

Question 1

Discuss the principles and importance of magnification, resolution, and contrast in microscopy

Answer 1

1. Magnification: apparent increase in size
2. Resolution: resolving power, or ability to distinguish two
   objects that are very close together
3. Contrast: determines how easily cells can be seen

Question 2

Compare and contrast light microscopes, electron microscopes, and scanning probe microscopes

Answer 2

1. Light microscope; can magnify 1,000x
2. Electron microscope; can magnify more than 100,000x
3. Scanning probe microscope; can produce images of
   individual atoms on a surface

Question 3

Describe the principles of a wet mount, a simple stain, the Gram stain, and the acid-fast stain

Answer 3

1. Wet mount uses a drop of liquid specimen overlaid with a coverslip
   - Allows observation of living organisms
   - Can be difficult to see when they are colorless
2. Simple staining uses a single dye to stain the specimen

3 . Gram stain most widely used for bacteria & reflects fundamental difference in cell wall structure
- two groups: Gram- (+) bacteria and Gram-(-) bacteria

4. Acid-fast stain used to detect organisms that do
   not readily take up dyes

Question 4

Describe the special stains used to observe capsules, endospores, and flagella

Answer 4

1. Capsule stain allows observation of gel-like layer that surrounds some microbes
2. Endospore stain allows visualization of endospores, resistant dormant cells often formed by Bacillus and Clostridium
3. Flagella stain uses a substance that makes the dye adhere to thin flagella, making them visible

Question 5

Describe the benefits of using fluorescent dyes and tags

Answer 5

• some dyes bind to structures in all cells
• some are changed by cellular processes: can distinguish
  between living and dead cells
• Immunofluorescence uses fluorescent dye-antibody labels to tag a unique microbe protein

Question 6

Describe the common bacterial shapes and groupings, and their significance

Answer 6

• Coccus: spherical
• Rod: cylindrical
• Vibrio, spirillum, spirochete, pleomorphic: squiggles

Question 7

Describe two multicellular associations of bacteria

Answer 7

1. Myxobacteria form swarms of cells that glide over moist
   surfaces as a pack
2. Most bacteria on surfaces in natural habitat form polymer-
   encased communities called biofilms

Question 8

Describe the chemistry and structure of peptidoglycan

Answer 8

A macromolecule that provides strength to the cell wall; it is found only in bacteria
- alternating subunits such as NAM + NAG

Question 9

Compare and contrast the structure and chemistry of the Gram-positive and Gram-negative cell walls

Answer 9

1. Gram (+): thick peptidoglycan layer teichoic acids extend above peptidoglycan layer &Gel-like material below peptidoglycan layer
2. Gram (-): Thin peptidoglycan layer, Outside is unique outer membrane

Question 10

Explain the significance of lipid A and the O antigen of LPS

Answer 10

1. Lipid A: recognizes the presence of invading bacteria
2. Antigen O: can be used to identify species or strains

Question 11

Explain how the cell wall affects susceptibility to penicillin and lysozyme

Answer 11

1. Penicillin interferes with peptidoglycan synthesis, Prevents cross-linking of adjacent glycan chain
2. Lysozome breaks bonds linking glycan chains

Question 12

Explain how the cell wall affects Gram staining characteristics

Answer 12

Gram-positive cell wall prevents crystal violet– iodine complex from being washed out

Question 13

Describe the cell walls of archaea

Answer 13

Archaea have variety of cell walls due to wide range of environments
- No peptidoglycan, but some have similar molecule pseudopeptidoglycan
- Many have S-layers that self-assemble
- Built from sheets of flat protein or glycoprotein subunits

Question 14

Compare and contrast the structure and function of capsules and slime layers

Answer 14

1. Capsule: distinct, gelatinous
2. Slime layer: diffuse, irregular
   - Gel-like layer outside cell wall protects or allows attachment
   - Most composed of glycocalyx (sugar shell), but some are polypeptides

Question 15

Describe the structure and arrangements of flagella, and explain how they are involved in chemotaxis

Answer 15

Flagella involved in motility
- Spin like propellers to move cell
- Numbers & arrangements help with characterization of bacteria

Three parts of bacterial flagellum:
- Basal body: anchors to cell wall and cytoplasmic membrane
- Hook
- Filament: made up of flagellin subunits

Question 16

Compare and contrast the structure and function of fimbriae and sex pili

Question 17

Describe the structure and function of the chromosome, plasmids, ribosomes, storage granules, gas vesicles, and endospores

Question 18

Describe the significance and processes of sporulation and germination

Question 19

Describe the structure and function of eukaryotic ribosomes, the cytoskeleton, flagella, and cilia

Question 20

Describe the function of the nucleus, mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes