Chapter 4. Microscopy

What does resolving power mean?

The ability to distinguish adjacent objects as separate.

What is the resolving power of the human eye vs. light microscope?

Eye ≈ 0.2 mm; Light microscope ≈ 0.2 µm.

What improves resolution in microscopy?

Shorter wavelength of light/electrons.

What does a bright-field microscope require to visualize most specimens?

Staining (specimens usually fixed and dead).

What microscope uses a hollow cone of light and makes specimens appear bright against a dark background?

Dark-field microscope.

Which microscope is best for thin spirochetes like Treponema pallidum?

Dark-field microscope.

Which microscope shows living, unstained cells and differences in refractive index?

Phase-contrast microscope.

What is the advantage of differential interference contrast (DIC) microscopy over phase contrast?

Provides a 3D effect with more detail.

What do fluorescence microscopes use to visualize specific antigens or antibodies?

Fluorochromes (e.g., FITC, Rhodamine, DAPI).

What is the difference between direct and indirect fluorescent antibody (FA) tests?

Direct detects microbial antigen; Indirect detects patient antibodies.

What microscopy technique uses lasers and computers to create 3D blur-free images of cells?

Confocal scanning microscopy.

What type of microscopy allowed scientists to break the diffraction limit of light (<20 nm)?

Super-resolution fluorescence microscopy (2014 Nobel Prize).

Which electron microscope is best for internal cell structures?

Transmission Electron Microscope (TEM).

What is the resolution limit of TEM?

<0.2 nm.

Which electron microscope is best for surface details and 3D images?

Scanning Electron Microscope (SEM).

What kind of stains use basic dyes like crystal violet, methylene blue, or safranin?

Simple stains.

What kind of stain colors the background instead of the specimen?

Negative stain (acidic dye).

Which stain differentiates bacteria based on cell wall structure (peptidoglycan)?

Gram stain.

What color do Gram-positive vs. Gram-negative bacteria appear after staining?

Gram+ = purple; Gram– = red/pink.

What differential stain is used for Mycobacterium species?

Acid-fast stain.

What color do acid-fast bacteria appear after staining?q

Red (non–acid-fast = blue).

Which stain uses India ink or Quellung reaction to visualize bacterial capsules?

Capsule stain.

Which stain highlights bacterial flagella by making them thicker?

Flagella stain.

Which stain uses malachite green and heat to visualize spores?

Endospore stain.

What are the three most common bacterial shapes?

Cocci (spheres), bacilli (rods), spirals.

What is a comma-shaped bacterium called?

Vibrio.

What is the difference between spirilla and spirochetes?

Spirilla = rigid spirals; Spirochetes = flexible spirals.

What bacterium forms Chinese-letter arrangements?

Corynebacterium.

What grouping describes grape-like clusters of cocci?

Staphylococci.

What grouping describes chains of cocci?

Streptococci.

What grouping describes four cocci in a square?

Tetrad.

What grouping describes eight cocci in a cube-like packet?

Sarcina.

About how big is E. coli?

2 µm × 0.7 µm.

What is the size of a human red blood cell (RBC)?

8 µm.

What is the approximate size of Staphylococcus aureus?

0.7 µm.

What is the size range of viruses?

18 nm (smallest, Parvovirus) to 300+ nm (poxvirus, giant viruses up to 1,500 nm).

What is the smallest known free-living bacterium?

Mycoplasma (~150 nm).

What is the largest known bacterium?

Thiomargarita namibiensis (~1 mm).

What protozoa can reach 5–6 cm in size?

Foraminifera.

What fungus is called the “humongous fungus” and spans 2,384 acres?

Armillaria ostoyae.