LAB 12: BACTERIA, PROTISTS, AND FUNGI

LAB 12: BACTERIA, PROTISTS, AND FUNGI

PART 1: BACTERIA

Characteristics of Bacteria

  • Bacteria are microscopic, single-celled organisms found universally in various environments.
  • Shapes of bacteria:
    • Cocci: round-shaped
    • Bacilli: rod-shaped
    • Spirilli: spiral or helical-shaped

Classification of Bacteria

  • Bacteria can be classified based on the composition of their cell walls:
    • Bacterial cell wall composition influences their reaction to stains, particularly in the Gram staining technique.

Gram Staining Technique

  • Bacteria that absorb crystal violet (stain) and appear purple:
    • Classified as Gram-positive.
    • Possess thick cell walls primarily made of peptidoglycan.
  • Bacteria that absorb safranin (counterstain) and appear pink/red:
    • Classified as Gram-negative.
    • Possess thin or nonexistent peptidoglycan cell walls.

Cyanobacteria

  • A group of large, Gram-negative, photosynthetic bacteria.
  • Habitat: often found in water or moist environments.
  • Characteristics of cyanobacteria:
    • Can be single-celled, colonial, or filamentous.
    • Examples of Cyanobacteria:
    • Nostoc: can exist as colonies or filaments and has the ability to fix nitrogen.
    • Oscillatoria: filamentous cyanobacteria that can oscillate to orient towards light.

Materials Required for the Lab

  1. Mixed population bacterial slide
  2. Nostoc prepared slide
  3. Oscillatoria prepared slide

Procedure of the Lab

  1. Obtain and examine the mixed population bacterial slide:
    • Identify bacterial cells with each of the three shapes (cocci, bacilli, spirilli).
    • Identify Gram-positive and Gram-negative bacteria.
  2. Obtain and examine a Nostoc prepared slide using scanning, low, and high power.
  3. Obtain and examine an Oscillatoria prepared slide using scanning, low, and high power.

Results

  1. Draw a picture of what you observe on the mixed population bacteria slide under high power.
  2. Draw a picture of what you observe on the Nostoc prepared slide under high power.
  3. Draw a picture of what you observe on the Oscillatoria prepared slide under high power.

Questions for Review

  1. Why is it helpful to use stains to classify bacteria?
    • Stains reveal the cell wall structure and help determine if bacteria are Gram-positive or Gram-negative.
  2. Are Nostoc single-celled, colonial, or filamentous bacteria?
    • Nostoc can be colonial or filamentous.
  3. Are Oscillatoria single-celled, colonial, or filamentous bacteria?
    • Oscillatoria are filamentous bacteria.