Study Notes on Protists

Introduction to Protists

• Protists are eukaryotic organisms distinct from animals, plants, and fungi.

• Over 100,000 described species; unclear number of undescribed species.

• High potential for diversity due to varied ecological roles.

Protist Cell Structure

• Protist cells are complex, mostly unicellular, with some multicellular forms.

• Structures vary: some are multinucleated and may behave as simple multicellular organisms.

Cell Protection

• Surrounded by various protective structures: membranes or walls, glassy shells, or pellicles.

Motility

• Various locomotion methods:

  • Paramecium: cilia

  • Amoeba: pseudopodia

  • Euglena: flagellum

Metabolism

• Nutrition types:

  • Photoautotrophs: photosynthetic.

  • Mixotrophs: both photosynthetic and heterotrophic.

  • Heterotrophs: consume organic material.

  • Saprobes: absorb nutrients from decaying matter.

Reproduction

• Asexual: binary fission (transverse/longitudinal), budding.

• Sexual: involves meiosis and fertilization; often occurs under stress or unfavorable conditions.

Habitat

• Primarily aquatic (freshwater, marine), some in soil or as parasites.

Classification

• Six supergroups within Eukaryota, believed to be monophyletic.

Excavata

• Includes asymmetrical single-celled organisms with a feeding groove.

• Subdivisions: diplomonads, parabasalids, euglenozoans.

Chromalveolates

• Likely arose via secondary endosymbiosis; includes important photosynthetic organisms.

• Divided into alveolates and stramenopiles.

Alveolates

• Characterized by alveoli beneath the membrane; includes dinoflagellates, apicomplexans, ciliates.

Dinoflagellates

• Can be photosynthetic or heterotrophic; notable for bioluminescence.

Ciliates

• Utilize cilia for feeding and movement (e.g., Paramecium).

Stramenopiles

• Defined by hairy flagella; include diatoms and brown algae.

Diatoms

• Unicellular with silica walls; contribute significantly to the biological carbon pump.

Brown Algae

• Multicellular, marine; possess complex life cycles including alternation of generations.

Rhizaria

• Comprise amoebas with pseudopodia for feeding and movement.

Archaeplastida

• Includes red and green algae, ancestors of land plants.

Amoebozoans

• Characterized by lobe-shaped or tubular pseudopodia.

Opisthokonts

• Includes choanoflagellates, resembling the common ancestor of animals.

Ecological Roles

• Primary Producers: contribute to global photosynthesis.

• Decomposers: return nutrients to ecosystems, crucial for plant growth.

• Parasitic roles: can cause diseases such as malaria and plant infections.