Protozoa/Protozoan Notes

Protozoa/Protozoan

• Eukaryotes, like human cells.
• Treatments can have greater side effects due to similarity to human cells.

General Terms

• Mode of Transmission: How the organism spreads from host to host. Describes how an organism spreads from host to host (important for the exam).
• Host: An organism infected with a pathogen that develops symptoms and can spread it.
• Reservoir: A lower-level organism (compared to humans) that indirectly transmits the pathogen, often without developing symptoms. Transmits through stool or something of that nature.
• Vector: Often an insect, a lower-level organism that directly transmits the pathogen, usually by a bite.

Examples:

• Yersinia pestis (Bubonic Plague):

  • Rats: Reservoir
  • Fleas: Vector
  • Humans: Host (cutaneous, bubonic, or pneumonic plague)

• Ticks are arachnids (eight legs) that transmit diseases like Lyme disease.

• Mild winters increase insect populations, including ticks.

• Lyme disease can be treated aggressively, especially early in the infection.

• Lyme disease can remain dormant for a long period and then start causing disease.

General Characteristics (Kingdom Protista/Protozoa)

• All single-celled organisms.
• Eukaryotes (cells structured like ours).
• Lack chlorophyll; cannot undergo photosynthesis.
• Free-living in marine, freshwater, or terrestrial environments.
• Require high moisture levels.
• Some species are parasites, gaining energy from a host while causing harm.

Structure and Reproduction

• Lack a rigid cell wall; may have a flexible cell wall.
• Shape is determined by the rigidity/flexibility of the cytoskeleton.
• Complex reproductive life cycles, often requiring a host.

Cell Shapes

• Cyst:
  • Resting form produced under adverse conditions. Cytoplasm becomes dormant with a hard outer coating.
  • Breaks open under favorable conditions to release a trophozoite.
• Trophozoite:
  • Mature, vegetative form of the cell; can carry out all cellular functions, including sexual reproduction.
• Sporozoite:
  • Immature, vegetative form; can perform all functions except sexual reproduction (only asexual).

Reproduction Types

• No distinct genders, but have mating types (e.g., type one and two).
• Sexual reproduction occurs if another mating type is present.
• Asexual reproduction occurs if no other mating type is present.

Schizogony

• Nucleus replicates multiple times inside the cell; the cytoplasm divides among the new nuclei.
• Results in many parasites being released simultaneously within a host.
• 1 cell can become 10-20 cells in a short time.

Classification

• Primarily based on mode of motility.

Four Groups

• Zooflagellates:
  • Move by flagella which are similar to bacterial flagella but not turned on and off based on the environment.
  • Flagella is used for movement.
  • The use of flagella depends on organism and life cycle.
  • Flagella can be used for moving, acting like sensory receptors and to attach to things, and food gathering.
• Ciliates:
  • Move by cilia arranged in rows. Beat in unison to propel the organism.
  • Example: Paramecium.
  • Oral groove cilia sweep food into the cell.
• Sarcodynes/Sarcodyna:
  • Move by pseudopodia (cytoplasm streams forward, changing the shape).
  • Example: Amoeba.
  • Cytoplasm streams in the direction of movement or food, engulfing it.
• Sporozoa:
  • Move via cysts, spores, or sporozoites.
  • Non-motile on their own.
  • Move between hosts typically via cysts in diarrhea.