AC

Chapter 5: Eukaryotic Cells and Microorganisms

Origins of Eukaryotic Cells

  • Endosymbiotic theory: eukaryotes resulted from one prokaryotic cell engulfing another, living symbiotically, and evolving together. Organelles originated from these trapped prokaryotic cells.

The History of Eukaryotes

  • First appeared ~2 \times 10^9 years ago, evolving from prokaryotes via symbiosis.

The Eukaryotic Cell

  • Components: cell wall (in some), cytoplasmic membrane, mitochondrion, nuclear membrane, nucleus, ribosomes, endoplasmic reticulum, cytoplasm, Golgi complex.

Concept Check: Endosymbiosis theory

  • Question: Which event occurred first according to the endosymbiosis theory?

    • Answer: Formation of a membrane around genetic material (nuclear enclosure).

Survey of Eukaryotes

  • Fungi

  • Algae

  • Protozoa

  • Parasitic worms

Fungi

  • Mostly harmless heterotrophic saprobes (live off dead organic matter).

  • Some are parasites (none obligate).

  • Mycoses: fungal infections.

Common Fungal Infections

  • Athlete’s Foot & Ring Worm: Trichophyton\ mentagrophytes

  • Candidiasis (vaginal yeast, oral thrush): Candida\ albicans

  • Aspergillosis: Aspergillus (respiratory, allergy)

  • Blastomycosis: Blastomyces (respiratory, Ohio/Mississippi river valleys)

  • Valley Fever / Coccidioidomycosis: Coccidioides (respiratory, Southwestern US)

  • Histoplasmosis: Histoplasma (respiratory, from bird/bat droppings in soil)

Algae

  • Free-living in water; basis of aquatic food webs; produce atmospheric O_2.

  • Dinoflagellates: can cause red tides, produce neurotoxins.

Algae & Toxins

  • Neurotoxins: interfere with nerve action.

  • Paralytic Shellfish Poisoning (PSP): caused by eating shellfish with dinoflagellates (saxitoxin); can cause respiratory failure.

  • Respiratory irritation: dinoflagellates (brevetoxin) in surf zone.

Protozoa Life Cycle

  • Trophozoite: motile, feeding stage.

  • Encystment: dormant resting stage (cyst) in unfavorable conditions.

  • Excystment: reactivation of trophozoite.

Protozoan Pathogen: Malaria

  • Genus: Plasmodium. Transmission: mosquito vector.

  • Resistance: sickle-cell trait confers resistance.

  • Symptoms: Fever, flu-like, anemia, jaundice; untreated can lead to organ failure, death.

Concept Check: Dormant form of protozoa

  • Question: The dormant form of protozoa are called___.

    • Answer: cysts.

Parasitic Worms (Helminths)

  • Collective term for tapeworms, flukes, and roundworms.

  • Morphology: Flatworms (thin, segmented) and Roundworms (elongate, cylindrical).

Parasitic Flatworms – Trematodes (Flukes)

  • Flattened, ovoid worms with sucking mouthparts. Cause liver/lung disease.

  • Transmission: ingestion of contaminated raw fish, crustaceans, or vegetables.

Parasitic Flatworms – Cestodes (Tapeworms)

  • Intestinal infection: larvae in intestines (nausea, weakness, weight loss).

  • Invasive infection: cysts in tissues/organs (organ failure).

  • Transmission: contaminated food or water.

Parasitic Roundworms

  • Ascariasis (Ascaris\ spp.): intestinal infection; widespread with poor sanitation; transmission: contaminated soil.

  • Hookworm disease (Ancylostoma\ spp.): common intestinal infection; widespread in tropics/subtropics; transmission: soil to bare feet.

Prevention of Helminth-Associated Disease

  • Prevent fecal contamination (sewage, latrines, water treatment).

  • Prevent contact with infested water.

  • Cook/freeze food thoroughly.