Lecture Notes on Protists

Protist: Informal name for a group of mostly unicellular eukaryotes.
Classification Changes: Advances in eukaryotic systematics have significantly altered the classification of protists.
Polyphyletic Group: Protists constitute a polyphyletic group, meaning they are grouped together by traits rather than a common ancestor.

Diversity: Protists exhibit more structural and functional diversity than any other eukaryotic group.
- Cellular Structure: Most protists are unicellular, but some are colonial or multicellular.
- Types of Protists:
- Animal-like Protists: Example: amoeba.
- Plant-like Protists: Example: giant kelp.
- Fungi-like Protists: Example: slime mold.
- Complexity: Single-celled protists can be very complex, with all biological functions carried out by organelles within each cell.

Nutritional Types:
- Photoautotrophs: Protists that contain chloroplasts.
- Heterotrophs: Absorb organic molecules or ingest larger food particles.
- Mixotrophs: Combine photosynthesis and heterotrophic nutrition.
Reproduction: Protists reproduce both asexually and sexually, with processes including meiosis and fertilization.

Mitochondria and Chloroplasts: Some protists lack or have lost mitochondria and/or chloroplasts.
- Endosymbiotic Relationships: These protists form relationships with bacteria or algae, replacing lost organelles.
- Example: Mixotricha paradoxa lives in a termite gut and is composed of multiple organisms:
- Three bacterial ectosymbionts for locomotion.
- At least one endosymbiont to help digest cellulose in wood.

Understanding Evolution: The relationships among protist groups are rapidly evolving.
Supergroups Hypothesis: All eukaryotes, including protists, can be divided into supergroups.

Origin: Descendants of a heterotrophic protist that had an endosymbiotic relationship with a cyanobacterium.
Included Species: Red algae and green algae (chlorophytes and charophytes).
Characteristics:
- Red and green algae can be unicellular, multicellular, or colonial.
- Exhibit various life cycles, including alternation of generations.

Gametangia: Structures that generate gametes.
Syngamy: Fusion of gametes.
Life Cycle: Zygote (2n) undergoes mitosis and meiosis to produce gametophytes (1n) leading to the formation of sporophytes (2n).

Characteristics: Typically multicellular, lacking flagella and having phycoerythrin, which gives them reddish coloration.
Color Variations: Can range from greenish-red in shallow waters to dark red or almost black in deeper waters.
Habitat: Most abundant large algae in tropical coastal waters.

Color: Named for their grass-green chloroplasts.
Relation to Plants: Green algae are the ancestors of land plants.
Classification: A paraphyletic group consisting of charophytes and chlorophytes.
- Charophytes: Closely related to land plants.

Diversity: Includes unicellular, multicellular, and colonial species.
Movement: Generally characterized by pseudopodia extending in tubes or flat lobes.
Inclusion: This group encompasses both amoebas and slime molds.

Historical Classification: Once categorized with fungi; DNA analysis shows resemblance is due to convergent evolution.
Lineages: Two types of slime molds exist:
- Plasmodial Slime Molds.
- Cellular Slime Molds.

Appearance: Many are brightly pigmented (yellow or orange).
Life Cycle:
- Form a plasmodium, an undivided mass containing many diploid nuclei.
- Extend pseudopodia to engulf food through phagocytosis.

Germination: Produces cells that can alternate between amoeboid and flagellated forms.
Spores (1n): Result from meiosis within the sporangium, creating haploid spores.
Zygote (2n): Formed by fertilization from either cell type, leads to a plasmodium.

Structure: Form multicellular aggregates with cell membranes separating them.
Feeding: Cells feed individually yet can gather to migrate and create a fruiting body.

Origin: Evolved from a common ancestor that engulfed a photosynthetic red alga (secondary endosymbiont event).
Includes:
- Important photosynthetic organisms like diatoms and brown algae (giant kelp).
- Significant disease agents affecting plants and animals.

Morphology: Diverse forms with two flagella and cellulose plates.
Habitat: Abundant in marine and freshwater phytoplankton.
Nutritional Modes: Include phototrophs, mixotrophs, and heterotrophs.
Impact: Toxic "red tides" caused by blooms, bioluminescence is generated when stressed.

Structure: Unicellular algae with a distinctive two-part, glass-like silicon dioxide wall.
Example Species: Triceratium morlandii.