Untitled

Chapter 28: Protists

Overview

  • Protist Definition: An informal term referring to all eukaryotes that are not classified as plants, animals, or fungi.
  • Diversity: Much of protistan diversity can be attributed to endosymbiosis, where one organism lives inside another.
  • Supergroups Overview: Protists are categorized into four major supergroups: Excavata, SAR, Archaeplastida, and Unikonta.

Key Concepts and Questions

  • Metabolic Characteristics:
    • Compare metabolic characteristics across Excavata, SAR, Archaeplastida, and Unikonta.
  • Physical Characteristics:
    • Identify distinctions in physical traits among Excavata, SAR, Archaeplastida, and Unikonta.
  • Plastid Evolution:
    • Discuss the evolution of plastids and their origins.
  • Charophyta & Chlorophyta:
    • Define and distinguish Charophyta and Chlorophyta.
  • Algal Types:
    • Differentiate between red and green algae.
  • Secondary Symbiosis:
    • Explain the process and implications of secondary symbiosis.
  • Atmospheric Contributions:
    • Describe how certain protists contribute to atmospheric conditions.

Concept 28.1: Eukaryotic Structure and Function

  • Unicellular Nature: Most eukaryotes are single-celled; protists exhibit extreme structural and functional diversity.
  • Nutritional Diversity: Protists include:
    • Photoautotrophs: possess chloroplasts.
    • Heterotrophs: absorb organic molecules or ingest food.
    • Mixotrophs: combine photosynthesis and heterotrophic nutrition.
  • Reproductive Strategies:
    • Asexual reproduction in some; sexual and asexual phases in others.

Endosymbiosis in Eukaryotic Evolution

  • Endosymbiosis: Defined as a relationship where one organism lives inside another's cells. Evidence suggests that:
    • Mitochondria originated from engulfed aerobic bacteria.
    • Plastids evolved when a heterotrophic eukaryote engulfed photosynthetic cyanobacteria.
  • Secondary Endosymbiosis: Occurs when red and green algae are ingested by heterotrophic eukaryotes, leading to varied lineages.

Four Supergroups of Eukaryotes

  • Excavata: Includes three clades – parabasalids, diplomonads, and euglenozoans.
  • SAR: Encompasses three large clades – Stramenopila, Alveolata, and Rhizaria.
  • Archaeplastida: Comprises red and green algae and plants.
  • Unikonta: Comprises amoebas, animals, fungi, and protists related to animals or fungi.

Concept 28.2: Excavates

  • General Characteristics: Excavates are characterized by their cytoskeleton and often possess an excavated feeding groove. Includes:
    • Diplomonads: Lack plastids, possess reduced mitochondria (mitosomes). Exemplar: Giardia intestinalis (intestinal parasite).
    • Parabasalids: Possess hydrogenosomes; exemplified by Trichomonas vaginalis (sexually transmitted parasite affecting 140 million globally).
    • Euglenozoans: Defined by a spiral or crystalline rod in flagella; include predatory heterotrophs and photosynthetic autotrophs like Euglena.

Concept 28.3: SAR

  • Monophyletic Group: Defined by DNA similarities, includes:
    • Stramenopiles: Features include “hairy” and “smooth” flagella. Important groups include diatoms, oomycetes, and brown algae.
    • Alveolates: Characterized by alveoli beneath the plasma membrane; includes dinoflagellates, apicomplexans, and ciliates.
    • Rhizarians: Defined as amoebas with threadlike pseudopodia; key groups include radiolarians, forams, and cercozoans.
Stramenopiles in Detail
  • Diatoms:
    • Unicellular algae with silicon dioxide walls, significant in phytoplankton contributions to CO2 levels.
    • Photosynthetic activity helps regulate global environments, and diatom blooms can lead to ecological impacts.
  • Brown Algae:
    • Largest and most complex multicellular algae, important for food production and ecological balance.
Alveolates in Detail
  • Dinoflagellates:
    • Important phytoplankton components, causing red tides that can harm aquatic life.
  • Apicomplexans:
    • Mostly animal parasites spreading through sporozoites; Plasmodium (malaria causing agent) affects millions.
  • Ciliates:
    • Use cilia for movement and feeding, characterized by distinct nuclei types (micronuclei and macronuclei).
Rhizarians in Detail
  • Radiolarians:
    • Possess silica skeletons, play crucial roles in marine ecosystems.
  • Forams:
    • Have porous calcium carbonate shells; contribute to fossil records and environmental changes over time.
  • Cercozoans:
    • Includes important mixotrophic protists like Paulinella chromatophora.

Concept 28.4: Archaeplastida

  • Origins: Photosynthetic protists gave rise to red and green algae; plants share a close ancestry with green algae.
  • Red Algae:
    • Characterized by phycoerythrin, notable for their multicellular nature and reproductive alternation.
  • Green Algae:
    • Focus on their structural similarity to plants through chloroplasts, complex life cycles, and mechanisms of size evolution.

Concept 28.5: Unikonts

  • Major Clades: Includes Amoebozoans (e.g., tubulinids, slime molds) and Opisthokonts (animals and fungi).
Amoebozoans in Detail
  • Tubulinids: Common amoebas with diverse feeding habits.
  • Slime Molds: Significant for studying multicellularity; includes plasmodial and cellular slime molds.

Concept 28.6: Ecological Roles of Protists

  • Symbiotic Relationships: Some protists have beneficial roles (e.g., aiding coral reefs) while others are involved in diseases.
  • Photosynthetic Roles: Crucial for aquatic ecosystems, affecting food chains and ecological health.
  • Impact of Climate Change: Warming temperatures threaten the stability of protist populations and related ecosystems.

Summary of Key Features Across Supergroups

  • Excavata: Diplomonads and parabasalids with modified mitochondria (e.g., Giardia, Trichomonas).
  • SAR: Includes notable groups like diatoms known for habitat contributions and ecological importance.
  • Archaeplastida & Unikonta: Focus on connections to plant lineages and animal/fungal relationships.