61.5.2.Algae

PLANT-LIKE PROTISTS

Definition and Classification

  • Protists are eukaryotes that are not classified as plants, fungi, or animals.

  • They were the original eukaryotes and are considered a diverse group.

  • Protists are NOT monophyletic.

Types of Protists

  • Unicellular: Most protists fall into this category.

  • Multicellular: Some protists are multicellular or exist in colonies.

  • Multinucleate: Certain protists possess multiple nuclei.

Nutritional Modes

  • Autotrophic (Photoautotrophic): Some protists can produce their own food through photosynthesis.

  • Heterotrophic: Many protists obtain nutrients by consuming organic material.

  • Mixotrophic: Some protists can perform both autotrophic and heterotrophic nutrition.

Habitats

  • Most protists are aquatic (marine or freshwater).

  • Some reside in terrestrial environments, often in moist soil.

  • Certain protists live within other organisms, acting as mutualists or parasites.

THE TREE OF LIFE

  • Major groups include:

    • Excavata

    • Discicristata

    • Alveolata

    • Stramenopila

    • Rhizaria

    • Plantae

    • Fungi

    • Animalia

    • Amoebozoa

Traditional Groupings of Protists

  • Protozoans: Animal-like protists.

  • Slime molds: Fungus-like protists.

  • Algae: Plant-like protists (focus of lecture).

  • Note: These groupings are also NOT monophyletic.

EUGLENIDS

  • Characteristics:

    • Unicellular mixotrophs.

    • Move using one long flagellum and a short vestigial flagellum (non-functional for movement).

    • Asexually reproduce.

    • Lack a cell wall; have a pellicle (protein sheet) for support and flexibility.

  • Habitat: Mostly freshwater, few marine, and part of phytoplankton.

  • Special Features:

    • Contractile vacuoles to expel water.

    • Eyespot (stigma) for light detection.

    • Functional mitochondria and chloroplasts.

DINOFLAGELLATES

  • Characteristics:

    • Unicellular autotrophs.

    • Move using two flagella located in perpendicular grooves.

    • Asexually reproduce.

    • Cell wall composed of cellulose.

  • Habitat: Mostly marine; part of phytoplankton.

Mutualism with Coral

  • Zooxanthellae are dinoflagellates living in coral tissues.

    • Benefits for zooxanthellae:

      • Shelter from corals

      • Access to nitrogenous compounds from coral waste

    • Benefits for coral:

      • Organic nutrients from photosynthesis

      • Stimulation for growth

Bioluminescence and Red Tides

  • Bioluminescence: Seen as a form of defense at night in agitated water.

  • Red Tides: Caused by algal blooms; toxins can deplete oxygen and harm ecosystems.

  • Often linked to agricultural runoff.

DIATOMS

  • Characteristics:

    • Unicellular autotrophs with silica cell walls lined with pores.

    • Wall does not decompose after death.

    • Found in marine or freshwater environments; part of phytoplankton.

  • Reproduction: Generally asexual; occasional sexual reproduction.

GOLDEN ALGAE

  • Characteristics:

    • Unicellular or colonial mixotrophs.

    • Move using two flagella.

    • Cell wall of silica or calcium carbonate.

  • Habitat: Found in marine or freshwater; part of phytoplankton.

BROWN ALGAE

  • Characteristics:

    • Multicellular autotrophic seaweeds, largest of all protists.

    • Contain chlorophyll and fucoxanthin.

    • Cell wall of cellulose.

  • Growth: Reproduce sexually; possess specific anatomical structures:

    • Holdfast

    • Stipe

    • Blades

    • Pneumatocysts (air bladders)

Kelp Communities

  • Kelp beds are vital ecosystems known for their biodiversity.

    • The holdfast serves as an anchor and habitat for many organisms, such as snails and amphipods.

    • Kelp contributes significantly to ecosystem production and supports various feeding mechanisms.

RED ALGAE

  • Characteristics:

    • Multicellular autotrophic seaweeds containing phycoerythrin.

    • Found in deeper or warmer water than other algae.

    • Reproduce sexually.

Cell Walls

  • Red algae have cellulose walls and can have calcium carbonate or gelatinous substances like agar and carrageenan.

GREEN ALGAE

  • Chlorophytes:

    • Autotrophic; cell wall of cellulose.

    • Examples: Chlamydomonas (unicellular), Volvox (colonial).

  • Charophytes:

    • Closest relatives to land plants; multicellular autotrophs and cellulose cell walls.

OTHER COOL PROTISTS

  • Slime molds: Unique group with interesting life cycles.

  • Water molds: Distinct characteristics and habitats.

  • Plasmodium: Causes malaria, highlighting pathogenic protists.

  • Giardia: Causes intestinal infections, identifiable by structuring of flagella and nuclei.

  • Trichonympha: Noted for its symbiosis in the guts of termites.