Protists

Protists Overview

• Eukaryotes: Protists are complex cells with a nucleus.

• Habitat: Typically found in aquatic environments, can also reside in moist internal environments or as parasites.

• Cellularity:

  • Mostly unicellular

  • Colonial: Small groups of cells

  • Coenocytic: Multinucleate mass

  • Multicellular: Coordinated groups of cells

• Primary Types: Some protists are referred to as protozoans based on their characteristics.

Varied Lifestyles of Protists

• Free-living: Independent lifestyle.

• Mutualism: Both species benefit from the relationship.

• Commensalism: One organism benefits while the other is unaffected.

• Parasitism: A parasite derives nourishment from a host, often harming it in the process.

Locomotion and Nutrition

• Types of Movement:

  • Pseudopodia: Extensions of the cytoplasm for movement and feeding.

  • Flagella: Whip-like structures for propulsion.

  • Cilia: Hair-like structures for movement and feeding.

• Nutrition Types:

  • Autotrophic: Organisms that produce their own food.

  • Heterotrophic: Organisms that consume other organisms for energy.

• Reproductive Strategies: Most protists can reproduce both sexually and asexually, while some reproduce only asexually.

Classification of Protists

• Classification Challenges: Protists are difficult to classify due to their diversity.

• Classification Techniques:

  • Ultrastructure: Analyzed using electron microscopy.

  • Molecular Data: DNA sequencing insights.

• Current Classification: Protists are no longer viewed as a distinct kingdom but are divided into five "supergroups" of eukaryotes.

Protist Clades Overview

• Excavates:

  • Characteristics: Unicellular, flagella, unique mitochondria.

  • Examples: Diplomonads, parabasalids, euglenoids.

• Chromalveolates:

  • Characteristics: Diverse group with alveoli and stramenopiles.

  • Examples: Dinoflagellates, ciliates, diatoms, brown algae.

• Rhizarians:

  • Features: Amoeboid cells with tests, thread-like projections.

  • Examples: Foraminiferans and actinopods.

• Archaeplastids:

  • Includes: Red algae, green algae, and land plants.

  • Chloroplasts: Bounded by two membranes.

• Unikonts:

  • Includes: Certain amoebas, slime molds, animals, and fungi.

  • Features: Single posterior flagellum when present.

Excavates Clade

• Diplomonads:

  • Have one or two nuclei, no mitochondria nor Golgi complex, possess flagella.

  • Example: Giardia, intestinal parasite.

• Parabasalids:

  • Anaerobic, flagellated, often reside within other organisms.

  • Example: Trichomonas vaginalis, a human parasite.

• Euglenoids/Trypanosomes:

  • Unicellular, flagellated, some are photosynthetic.

  • Example: Trypanosoma brucei, causing African sleeping sickness.

Chromalveolates Clade

• Alveolates:

  • Characterized by alveoli beneath the cell membrane.

  • Includes dinoflagellates, apicomplexans, and ciliates.

• Stramenopiles:

  • Two flagella, one is hairy.

  • Includes diatoms and brown algae.

Specific Groups in Chromalveolates

• Dinoflagellates:

  • Marine, photosynthetic, with two flagella.

  • Cause "red tide" due to toxic blooms.

• Apicomplexans:

  • Non-motile, spore-producing parasites (e.g., Plasmodium causes malaria).

• Ciliates:

• Use cilia for movement, undergo conjugation for genetic exchange.

Rhizarians

• Foraminiferans: Thread-like projections used for motility and feeding, symbiotic with algae, form chalk accumulations.

• Actinopods: Marine organisms with long axopods for feeding.

Archaeplastids

• Red Algae: Multicellular and important for reef-building, no flagella.

• Green Algae: Diverse in form, chemically identical to plants.

Unikonts

• Choanoflagellates: Share characteristics with animals, are often free-swimming or sessile.

• Amoebozoa: Unicellular amoebas with pseudopodia, some are human parasites (e.g., Entamoeba histolytica).

• Slime Molds: Form multicellular aggregates under certain conditions, model organisms for studying cell signaling.