Lecture+10+slides

Lecture Overview

Introduction to Protists

• Today's lecture covers Chapter 28 focused on protists, following a review of Lecture 9.

• Key topics include the definition of protists, their diversity, and roles within ecosystems.

• Attendance will be recorded, and students may ask review questions during available time.

Lecture Outcomes

• By the end of the lecture, students should be able to:

  1. Describe the diversity of feeding and reproductive strategies of protists.

  2. Define endosymbiosis and describe the process involved.

  3. Recall examples for the four main groups of Protista: excavates, SAR (Stramenopiles, Alveolates, Rhizarians), algae, and unikonts.

  4. Describe the ecological roles of protists including symbiotic relationships and contributions to photosynthesis.

  • Tip: Key terms will be highlighted in bold to aid learning.

What are Protists?

• Definition: Protists are primarily single-celled eukaryotic organisms that do not fit into the categories of plants, animals, or fungi.

• They are no longer considered a discrete kingdom because many protists are more closely related to plants, animals, or fungi than to other protists.

• Most eukaryotic diversity comes from protists, making them a significant component of the tree of life.

Structural and Functional Diversity

• Protists exhibit more structural and functional diversity than any other eukaryotic group:

  • Unicellular Complexity: Unicellular protists perform all necessary life functions independently, making them the most complex eukaryotic cells.

  • Some possess unique organelles, such as ocelloids (light-sensitive structures) found in certain dinoflagellates and contractile vacuoles for osmoregulation.

• Nutritional strategies among protists vary widely:

  • Photoautotrophs: Contain chloroplasts for photosynthesis.

  • Heterotrophs: Absorb nutrients or ingest food particles.

  • Mixotrophs: Combine both nutritional strategies, exemplified by species like Rapaza viridis.

Reproductive Strategies

• Reproduction in protists can be asexual, sexual, or both:

  • Asexual reproduction predominates, while various sexual phases can occur depending on the type of protist.

Evolution of Protists

• Endosymbiosis Theory: This theory explains that mitochondria and plastids originated through the engulfing of bacteria by ancestral eukaryotic cells.

• Mitochondria evolved from proteobacteria, while plastids arose from cyanobacteria after being engulfed by a heterotrophic eukaryote.

  • Primary Endosymbiosis: The initial step that led to the formation of plastids involves the engulfment of a cyanobacterium.

  • Secondary Endosymbiosis: Involves the ingestion of red and green algae by other eukaryotes, leading to organisms with multiple membranes surrounding plastids.

Protist Diversity

Major Groups of Protists

• Excavata: Defined by cytoskeleton morphology, often with modified mitochondria or flagella.

  • Includes diplomonads (e.g., Giardia), parabasalids (e.g., Trichomonas), and euglenozoans (e.g., Euglena).

• SAR Clade: Consists of Stramenopiles, Alveolates, and Rhizarians.

  • Stramenopiles: Includes diatoms and brown algae, known for their importance in carbon cycling.

  • Alveolates: Distinguished by membrane-enclosed sacs under the plasma membrane; examples include dinoflagellates and ciliates.

  • Rhizarians: Mostly amoebas that move via pseudopodia, including forams and radiolarians.

• Archaeplastida: Encompasses red algae and green algae, which are crucial in ecosystems and directly relate to land plants.

• Unikonta: Comprised of

Unikonta: Comprised of two major groups: Amoebozoans and Opisthokonts.

• Amoebozoans: Characterized by their amoeboid movement and include slime molds and tubulinids. They play significant roles in soil and aquatic ecosystems, contributing to nutrient cycling.

• Opisthokonts: Includes animals, fungi, and related protists. Key features are the structure of their flagellum (if present), which is posterior. This group encompasses important organisms such as choanoflagellates, which are the closest relatives of animals.

Ecological Significance: Protists are critical in various ecosystems, serving as primary producers (e.g., phytoplankton) and forming symbiotic relationships with other organisms. Their contributions to global carbon cycling and nutrient dynamics are fundamental to sustaining biodiversity.

Lecture Information Coverage: The slides cover key aspects of protists, including their diversity, structural and functional characteristics, nutritional strategies, and reproductive methods. Major groups of protists (excavates, SAR clade, Archaeplastida, and Unikonta) are detailed along with examples. The ecological significance of protists, including their roles in ecosystems and contributions to global processes, is also highlighted. Students should refer to the lecture content for comprehensive understanding and examples that may not be fully captured in the slides.**