Lecture_10_slides

Lecture Overview

• Lecture Title: Protists

• Course: Bio 80, Lecture 10, Chapter 28

Plan for Today's Lecture

• Review of Lecture 9

• Lecture 10 Topics:

  • What are protists?

  • Protist diversity

  • Roles of protists

• Attendance

• Review Questions: Allocate time for student inquiries

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 and explain endosymbiosis.

3. Identify and provide examples of the four groups of Protista:

   • Excavates

   • SAR (Stramenopiles, Alveolates, Rhizarians)

   • Algae

   • Unikonts

4. Discuss roles of protists in ecosystems, focusing on symbiosis and photosynthesis.

Introduction to Protists

• Definition: Protists are informal groupings of eukaryotic organisms that are not classified as plants, animals, or fungi.

• Characteristics:

  • Most are single-celled eukaryotes with a nucleus and membrane-enclosed organelles.

  • They exhibit isolation of cellular functions and possess a well-developed cytoskeleton, allowing changes in shape.

  • Protists represent much of the eukaryotic diversity.

Structural and Functional Diversity

• Single-celled Complexity: Unicellular protists must perform all life functions independently.

• Organelles: Some protists possess unique organelles, such as the ocelloid in dinoflagellates or contractile vacuoles for water regulation.

• Nutritional Strategies:

  • Photoautotrophs: Protists with chloroplasts.

  • Heterotrophs: Absorb or ingest organic materials.

  • Mixotrophs: Combine photosynthesis and heterotrophic behavior.

• Reproductive Strategies: Examples include asexual, sexual, or combinations throughout life cycles.

Evolution of Protists

• Endosymbiosis: A significant evolutionary phenomenon where one organism resides within another. Mitochondria and plastids are believed to have evolved through such processes.

  • Plastids: Originated after mitochondrial development through the engulfment of cyanobacteria.

  • Secondary Endosymbiosis: Red and green algae were consumed by heterotrophic eukaryotes, leading to variations in plastid structures.

Protist Diversity

• Groups of Protists:

  • Excavata: Defined by unique cytoskeletal characteristics and feeding grooves. Includes diplomonads and parabasalids.

  • SAR Clade: Characterized by photosynthetic groups like diatoms and brown algae, along with organisms like ciliates and dinoflagellates.

  • Archaeplastida: Includes red and green algae that gave rise to land plants.

  • Unikonta: Encompasses amoebas and slime molds, as well as ancestors to animals and fungi.

Key Protistan Groups

• Excavates:

  • Characterized by modified mitochondria or unique flagella.

  • Examples include diplomonads (e.g., Giardia) and euglenozoans (e.g., Euglena).

• Stramenopiles:

  • Notable for their diverse functional roles, including critical carbon pumps of photosynthesis. Includes diatoms, brown algae (e.g., kelp), and oomycetes.

• Alveolates:

  • Defined by membrane-bound sacs beneath their plasma membrane. Groups include dinoflagellates (important for plankton communities) and ciliates (e.g., Paramecium).

• Rhizarians:

  • Distinguished by unique pseudopodia; includes foraminifera and radiolarians.

Roles of Protists in Ecosystems

• Symbiotic Relationships: Protists contribute to ecology as symbionts or parasites. For example, dinoflagellates nourish coral polyps.

• Photosynthesis: About 30% of Earth's photosynthesis is attributed to protists, making them crucial producers within aquatic ecosystems.

• Ecological Impact: Nutrient availability affects protist populations, leading to phenomena like red tides and dead zones caused by excessive growth in nutrient-rich conditions.

Conclusion

• Protists play vital roles in ecosystems both as symbiotic organisms and primary producers, highlighting their significance in environmental health and biodiversity.