Lesson 3 - Photosynthetic Prokaryotes

• In photosynthetic prokaryotes, infoldings of the plasma membrane act like thylakoids.
• Nitrogen-fixing bacteria (Rhizobium)
• Azolla houses Anabaena, a cyanobacterium

  • Azolla sp. (a tiny aquatic fern)
• Heterocyst - Site for nitrogen fixation.
• Akinete - Dormant cell, helps in asexual reproduction, formed during unfavorable conditions.
• Anabaena azollae (N-fixing bacterium)
• Cyanobacteria lack:

  • internal organelles
  • a discrete nucleus
  • histone proteins associated with eukaryotic chromosomes

  Like all eubacteria, their cell walls contain peptidoglycan
• Cyanobacteria have an elaborate and highly organized system of internal membranes which function in photosynthesis.
• Chlorophyll a and several accessory pigments (phycoerythrin and phycocyanin) are embedded in these photosynthetic lamellae, the analogs of

  the eukaryotic thylakoid membranes.
• Prochloron - a unicellular marine organism symbiotic on sea squirts (ascidians). Discovered in 1975. Contains chlorophlylls a and b; carotenoids
• Protists

  • 200 thousand species
  • Very diverse: microscopic algae and protozoa to giant kelps, brown algae that reach 75 meters (about 250 feet) in length.
• Most of the algae are autotrophic and photosynthesize as plants do. Some heterotrophic protists obtain their nutrients by absorption, as fungi do, whereas others resemble animals and ingest food.
• According to biologists, protists were the first eukaryotic cells that have evolved from prokaryotes.
• The first eukaryotes were probably zooflagellates, heterotrophic unicellular protists that have flagella.