Protozoa Overview and Morphology Quiz

Protozoa: A General Overview

• Protozoa belongs to the Kingdom Protista, are eukaryotic, unicellular, and heterotrophic.
• Protozoa perform all life functions within a single cell including reproduction, respiration, excretion, and movement.
• Protozoa vary in size and shape, some are visible with the naked eye, others require magnification.
• Protozoa are found in all moist habitats including oceans, soil, and fresh water.
• Most are non-pathogenic, but some can cause diseases.

Protozoa Morphology

• Protozoa are composed of a cytoplasmic body and a nucleus.
• Specialized structures within the cell are called organelles which carry out various life functions.
• Cytoplasm
  • Consists of an outer ectoplasm and inner endoplasm.
  • Ectoplasm
    • Is the outer layer, more transparent, less granular, and homogeneous.
    • Contains the plasma membrane which functions in movement, respiration, food intake, waste removal, and protection.
    • The ectoplasm is the origin of locomotion organelles:
      • Pseudopodia: temporary extensions of the ectoplasm found in Amoebas (subphylum Sarcodina).
      • Flagella: long, slender, whip-like structures found in subphylum Mastigophora.
  • Endoplasm
    • Is the inner layer, more granular, and contains organelles.
    • May contain:
      • Food vacuoles: for digestion.
      • Inclusions: such as red blood cells, bacteria, or other ingested materials.
      • Glycogen vacuoles: represent the storage form of glucose.
      • Chromatoidal bodies (or bars): dense structures composed of crystalline RNA and RNA-binding proteins.
• Nucleus
  • May be located centrally or eccentrically.
  • Has a karyosome (also known as an endosome) which may be surrounded by chromatin particles arranged in an achromatic network.
  • Compact nucleus: found in few protozoa, primarily in ciliates.
    • The chromatin granules are dense, so the nucleoplasm is not visible under light microscopy.
• Other Structures:
  • Macronucleus (in ciliates): Involved in general cell metabolism and daily activities.
  • Micronucleus (in ciliates): Responsible for sexual reproduction.

Protozoa Life Cycles

• Protozoa often exist in two developmental stages:
  • Trophozoite:
    • The motile, vegetative stage.
    • Replicates and feeds on host cells, responsible for pathogenic effects.
    • Delicate and cannot survive long outside the host.
  • Cyst:
    • The resting, non-motile stage.
    • Surrounded by a tough cell wall, making them resistant to unfavorable environments.
    • The infective stage for most protozoa.

Protozoa Reproduction

• Protozoa exhibit both asexual and sexual reproduction:
  • Asexual reproduction:
    • Binary fission: Protozoa divide into two roughly equal daughter cells. The plane of fission varies by species.
    • Multiple fission: The nucleus and organelles divide repeatedly, followed by cytoplasmic division (cytokinesis) which produces many daughter cells simultaneously.
    • Schizogony: A type of multiple fission in Apicomplexa (e.g. Plasmodium) with daughter cells called merozoites that can initiate further asexual replication (merogony) or sexual reproduction (gametogony).

Summary of Protozoa:

• Protozoa are diverse, unicellular eukaryotic organisms mostly found in moist environments.
• They have complex cell structures and reproduce through both asexual and sexual processes.
• Although most are not harmful, some cause significant diseases.

Test your knowledge on the general characteristics and morphology of protozoa. This quiz covers essential topics including their life functions, habitats, and cellular structures. Perfect for biology students looking to understand the diversity of this fascinating kingdom.