prokaryotes - simplest organisms  

• 2 main groups - archaebacteria, bacteria
• no distinct interior compartments
• perform photosynthesis, break down dead organisms, cause diseases

cell wall - surrounds most prokaryotic cells  

• peptidoglycan - sugar polymers cross-linked by polypeptides; found in bacteria walls
• protects cell, maintains shape, prevents overdose of water
• gram-positive bacteria - have thick, single-layered cell wall; turns purple from gram staining
• gram-negative bacteria - more complex bacteria w/ multilayered cell wall; doesn't turn purple, turns red
• drugs often destroy bacteria's cell wall to kill it
• disease-causing bacteria secrete a jellylike capsule of polysaccharides to allow it to cling to different surfaces

flagellum - long threadlike structure used by some prokaryotes to move  

• protein fibers extending from the bacteria cell
• could be more than 1 per cell, depending on the species of bacteria
• rotated like a screw to propel the cell forward
• uses proton gradient on the membrane to power the flagellum's mov't (process also used by some enzymes that produce ATP in mitochondria/chloroplasts)

prokaryotic interior organization - very simple, no membrane-bounded organelles  

• no interior support >> prokaryotic cell's strength depends on cell wall
• membrane performs much of the tasks done by organelles in eukaryotes
• prokaryote acts as a single unit (no specific task done only at a specific area)

eukaryotes - much more complex than prokaryotes  

• compartmentalization possible through endomembrane system and organelles
• vesicles - sacs that store/transport certain materials
• chromosomes - compact units of DNA
• cytoskeleton - internal protein support for the cell
• animals and some protists lack cell walls
• central vacuole - large sac holding proteins, pigments, waste in plants