BIOL1407_Sp25_Protists 6-1

Overview of Protists and Eukaryotes

• Eukaryotic cells have organelles and are complex compared to prokaryotic cells.

• Protists: informal group of mostly unicellular eukaryotes.

  • Classification of protists is not monophyletic; Protista is no longer valid as a kingdom.

• Four Supergroups of Eukaryotes:

  • Excavata

  • Archaeplastida

  • "SAR" Clade: Stramenopiles, Alveolates, Rhizarians

  • Unikonta

Structural and Functional Diversity

• Protists demonstrate more diversity than any other eukaryotic group.

  • Includes unicellular, colonial, and multicellular species.

• Nutritional Diversity:

  • Photoautotrophs: Contain chloroplasts.

  • Heterotrophs: Absorb organic molecules/invest larger particles.

  • Mixotrophs: Combine photosynthesis and heterotrophic nutrition.

• Reproduction:

  • Asexual and sexual reproduction observed in various protists.

Ecological Roles of Protists

• Protists are crucial to aquatic and moist terrestrial environments:

  • Producers: Key producers in aquatic ecosystems.

  • Consumers: Herbivores and carnivores.

  • Decomposers/Scavengers: Play roles in nutrient recycling.

  • Parasites/Pathogens: Some pathogenic species affect plants and animals.

Parasitic Protists

• Notable examples include:

  • Phytophthora ramorum: Causes sudden oak death.

  • P. infestans: Causes potato late blight, linked to the Irish famine.

  • Trypanosoma cruzi: Causes Chagas’ disease, evades host immunity via surface protein switching.

  • Plasmodium: Causes malaria, complex life cycle involving mosquitoes and humans.

Specific Types of Protists

Euglenids

• Characterized by 1-2 flagella.

• Capable of both autotrophic and heterotrophic nutrition.

Diatoms

• Unicellular algae with silicon dioxide shells.

• Major component of phytoplankton; abundant photosynthetic organisms.

  • Fossilized shells known as diatomaceous earth.

Brown Algae

• Includes giant kelp; resembles plants due to analogous structures.

Dinoflagellates

• Feature two flagella; cause red tides through blooms that produce toxins.

Apicomplexans

• Specialized organelles for penetrating host tissues; many are serious parasites.

Ciliates

• Move and feed using cilia; characterized by two nuclei.

Red Algae

• Multicellular, abundant in tropical coastal waters; reddened by pigments.

Green Algae

• Named for their green chloroplasts; ancestors of land plants; diverse habitats.

Overview of Protists and Eukaryotes

Eukaryotic cells, which are characterized by the presence of organelles, are significantly more complex than prokaryotic cells. These cells contain a defined nucleus and various membrane-bound organelles that perform specific functions, allowing for greater versatility and specialization.

Protists

Protists are an informal group encompassing mostly unicellular eukaryotes, although some are multicellular. The classification of protists is not monophyletic, meaning that Protista is no longer considered a valid kingdom due to the diverse evolutionary paths of its members. Protists play a critical role in ecosystems and span several clades that reflect their evolutionary history.

Four Supergroups of Eukaryotes:

1. Excavata: This supergroup includes organisms with unique feeding grooves and flagella. Members vary in nutritional modes, including some that are parasitic.

2. Archaeplastida: This group includes red and green algae, as well as land plants. It is characterized by the presence of chloroplasts derived from primary endosymbiosis.

3. "SAR" Clade: This group consists of Stramenopiles (such as diatoms and brown algae), Alveolates (including dinoflagellates and ciliates), and Rhizarians (like foraminiferans and radiolarians). These members are distinguished by shared genetic traits and structural characteristics.

4. Unikonta: This diverse group includes both amoeboid organisms and animals; it is characterized by the presence of a single flagellum in some cells (e.g., choanoflagellates).

Structural and Functional Diversity

Protists show a remarkable array of structural forms and functional abilities. They exhibit greater diversity than any other eukaryotic group, including:

• Unicellular organisms: Composed of a single cell capable of performing all life functions.

• Colonial arrangements: Groups of individual cells that may work together for survival but remain complete individual cells.

• Multicellular species: More complex forms that operate in larger collective structures, resembling plants or animals.

Nutritional Diversity:

• Photoautotrophs: These protists contain chloroplasts and perform photosynthesis to capture energy from sunlight, contributing significantly to global carbon fixation.

• Heterotrophs: These organisms absorb organic molecules or engulf larger particles for nutrition, playing essential roles in their ecosystems as consumers.

• Mixotrophs: These versatile organisms combine photosynthesis and heterotrophic nutrition, allowing them to thrive in varying environments.

Reproduction

Reproduction strategies in protists include both asexual (binary fission, budding) and sexual reproduction (fusion of gametes), increasing genetic diversity and adaptability in changing environments.

Ecological Roles of Protists

Protists play crucial roles in both aquatic and moist terrestrial environments:

• Producers: They form the base of food webs in aquatic ecosystems, generating organic matter through photosynthesis.

• Consumers: Many protists function as herbivores and carnivores, impacting population dynamics among other microorganisms.

• Decomposers/Scavengers: These organisms contribute to nutrient cycling by breaking down dead organic matter, releasing nutrients back into ecosystems.

• Parasites/Pathogens: Some protists are pathogenic and can have significant impacts on plants and animals, leading to various diseases.

Parasitic Protists

Notable examples of parasitic protists include:

• Phytophthora ramorum: A plant pathogen responsible for sudden oak death, which poses a threat to oak trees and other species in affected areas.

• P. infestans: This organism causes potato late blight and was infamously linked to the Irish famine, demonstrating the impact of diseases on human history.

• Trypanosoma cruzi: This protist is the causative agent of Chagas’ disease and can evade host immunity through a unique mechanism of surface protein switching, complicating treatment efforts.

• Plasmodium: Responsible for malaria, this protist has a complex life cycle that involves both mosquitoes and humans, making it a significant public health concern.

Specific Types of Protists

• Euglenids: Recognized by their 1-2 flagella, euglenids can switch between autotrophic and heterotrophic nutrition depending on environmental conditions.

• Diatoms: These unicellular algae possess silica shells and are a major component of phytoplankton, contributing largely to oceanic primary production. Fossilized diatom shells form diatomaceous earth, used commercially as a filtration aid.

• Brown Algae: Including species like giant kelp, brown algae possess structures similar to land plants, but are not closely related. They play vital roles in coastal ecosystems as habitat and food sources.

• Dinoflagellates: These protists, characterized by two flagella, can cause harmful algal blooms (red tides) that produce toxins affecting marine life and human health.

• Apicomplexans: This group contains protozoan parasites with specialized organelles for tissue penetration, many of which cause serious diseases in humans and animals.

• Ciliates: Notable for using cilia for movement and feeding, these organisms typically have two nuclei, allowing for complex behaviors and interactions.

• Red Algae: Mostly multicellular and abundant in tropical coastal waters, red algae are known for their distinctive pigments that give them their coloration.

• Green Algae: The ancestors of land plants, green algae feature green chloroplasts and are found in diverse habitats, ranging from freshwater to marine environments.