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Protozoan Groups and Single-Celled Organisms: ZOL1501

Overview of the Protists

Core Concepts
  • Evolutionary Relationships: Study of how different organisms are related through evolution.

  • Classification: Organizing life forms based on characteristics, morphology, and lineage.

  • Evolutionary Pressures and Adaptations: Factors that influence the evolution and adaptive radiation of species.

Assessment Criteria
  • Differentiate between important terms:

    • Protozoan Group: A classification for single-celled organisms that exhibit animal-like behavior.

    • Chlorophyta: A group of green algae in the plant kingdom.

    • Euglenozoa: A diverse class of flagellated protists that includes euglenids.

    • Dinoflagellate: A group of unicellular organisms that are known for their unique flagella.

    • Flagellum: Long, whip-like structures used for locomotion in some protists.

    • Morphology: The study of the form and structure of organisms.

  • Identify general body pattern (morphology) of protozoan groups.

  • Describe the position of protozoan groups relative to the animal kingdom.

  • Differentiate between three subphyla of protozoa and compare their biological importance to the animal kingdom.

  • Explain reproduction mechanisms in different protozoan groups.

The Protista Kingdom

  • Definition: Utilizes the term “Kingdom” Protista, referring to a kingdom of eukaryotic organisms that are primarily unicellular or simple multicellular.

  • Discussion whether it acts as a mixed-up kingdom with varied organisms.

Five Kingdoms (Whittaker 1969)

  • Plants: Eukaryotic, multicellular organisms that photosynthesize.

  • Animals: Eukaryotic, multicellular organisms that ingest food and are motile.

  • Fungi: Eukaryotic, multicellular organisms that absorb nutrients and are nonmotile.

  • Protists: Eukaryotic, unicellular, or multicellular organisms that absorb, ingest, or photosynthesize; can reproduce sexually and asexually.

  • Monera: Prokaryotic organisms that are unicellular and absorb or photosynthesize and can be motile or nonmotile.

Three Domains of Life (Woese 1970)

  • Eukarya: Includes plants, fungi, protists, and animals.

  • Bacteria: Heterotrophic bacteria and cyanobacteria (photosynthetic).

  • Archaea: Distinct from bacteria and eukaryotes, often extremophiles.

General Characteristics of Protozoa

  • Eukaryotic Structure: Most are unicellular but can also be multicellular, colonial, or filamentous.

  • Complexity: Display a range of sizes, morphologies, and nutritional modes; some, like kelp, can be macroscopic and structurally complex.

  • Cell Membrane: Resembles those of metazoans, indicating evolutionary relationships.

  • Cytoplasm:

    • Endoplasm: Inner semi-fluid part containing organelles.

    • Ectoplasm: Outer layer that is more gel-like, often visible in motile cells.

Nutritional Modes

  • Autotrophic: Organisms that produce their own food via photosynthesis.

  • Heterotrophic: Organisms that obtain food from other organisms.

  • Mixotrophic: Capable of both autotrophic and heterotrophic nutrition.

Reproductive Strategies

  • Asexual Reproduction: Predominant form through methods such as binary fission, multiple fission, budding, and plasmotomy.

  • Sexual Reproduction: Occurs in some species, allowing genetic variation.

  • Encystment: Formation of a protective cyst to withstand adverse conditions; can evolve rapidly.

Ecological Roles

  • Decomposition: Providing ecological service by breaking down organic materials, influencing nutrient cycling.

  • Human Health: Some protozoa cause diseases such as malaria and dysentery.

Phylogeny of Protists

  • Classification is complex and continues to evolve with new data; six supergroups have been identified:

    • Archaeplastida: Includes land plants and green/red algae.

    • Chromalveolates: Contains brown algae, diatoms, and some protozoans.

    • Excavates: Characterized by unique flagella.

    • Amoebozoa: Includes amoeboids and slime molds.

    • Rhizaria: Comprising foraminiferans and radiolarians.

    • Opisthokonts: Encompassing animals and fungi.

Locomotion Structures

Cilia
  • Armature responsible for motility formed in uniform structure across protist groups.

  • Exhibits power and recovery strokes for movement and food capture.

  • Able to facilitate efficient nutrient uptake and dispersal.

Flagella
  • Similar in function to cilia but usually longer with additional structures called mastigonemes for increased efficiency.

  • Operate through a rippling wave of movement; observed in organisms such as Euglena.

Pseudopodia
  • Temporary cellular extensions used for movement in amoebas, vital to feeding and locomotion.

  • Types of pseudopodia include:

    • Lobopodia: Broad, with distinct tips (observed in Amoeba).

    • Filopodia: Slender, lacking a hyaline cap and branched (facilitates cytoplasmic streaming).

    • Reticulopodia: Thin, forming a network structure.

    • Axopodia: Radiating spines, mainly for feeding purposes.

Reproduction Mechanisms

  • Study of asexual reproduction methods and their implications for survival in fluctuating environments.

  • Variation in reproduction, such as the formation, lifecycle of zygotes (e.g., in Chlamydomonas).

Summary of Protista Characteristics

  • Eukaryotic organisms that are typically unicellular with complex life cycles.

  • Significant role in ecological systems as primary producers and decomposers, yet are subject to classification challenges due to diversity in features and lifestyles.