protists

Unicellular

• Single eukaryotic cell organisms

• No specialized tissues

Colonial

• Loosely connected groups of individual cells

Coenocytic

• Can feature multinucleate mass of cytoplasm

Reproduction

• Most reproduce asexually, many sexually

• No sex organs

• Complex life cycles

Pseudopodia

• Cytoplasmic projections

• Extends, reversibly contracts

Flagella

• Whip like structure 

• Undulates or lashes

Cilia

• “Eyelash”

• Structure identical to eukaryotic flagella

• Length is shorter

Endosymbiotic  Theory

• Hypothesis, that certain organelles originated from symbiotic prokaryotes that lived inside other, free living prokaryotic cells

• Eukaryotic formed from union of small aerobic prokaryotes with larger anaerobic prokaryotes

• Protists were first eukaryotes

Symbiotic theory

• Different unicellular species developed a symbiotic relationship

• Lost the ability to survive independently

The cellularization theory

Unicellular cells with two nuclei developed membrane around each

The colonial theory

• Several cells of the same species separated during division and re-join each other

• Cells fail to separate during cell division

Increasing complexity

• Allows for cell differentiation and specialization

• Apoptosis ≠ Death of organism

Larger size organism

• Not dependent on diffusion for nutrients

Multicellularity

Symbiotic theory

The cellularization theory

The colonial theory

Increasing complexity

Larger size organism

Reduced exposure to external environment