Prokaryotes vs. Eukaryotes and Algae Characteristics

Prokaryotes vs. Eukaryotes

• Prokaryotes:

  • Cell wall usually contains peptidoglycan.
  • Nuclear division not by chromosome or nuclear membrane.
  • No sexual reproduction, but this process occurs in some bacteria.
  • Flagella, when present, lack a 9+2 structure.
  • Some can fix nitrogen (e.g., bacteria and blue-green algae).

• Eukaryotes:

  • Peptidoglycan absent.
  • Nuclear division usually by mitosis or meiosis.
  • Sexual reproduction is common.
  • Flagella have a characteristic 9+2 structure (9 outer + 2 inner).
  • Non can fix nitrogen (e.g., all other plants and animals).

Common Characteristics of Algae

• Algae range from tiny single-celled microalgae to giant seaweeds exceeding 50 meters.
• Defined as photosynthetic organisms (unicellular or multicellular).
• Lack specialized root, stem, and vascular bundles.
• Lack a diploid embryo stage.
• Lack sterile tissue surrounding reproductive structures.
• Zygote development occurs via mitosis or meiosis, not via embryo formation.

Rhodophyta (Red Algae)

• Abundant and diverse in warm tropical and subtropical areas.
• Some found in temperate and polar seas, including some unicellular forms in hot springs.
• Critical in coral reef building (encrusting, calcified corallines), contributing to consolidation.
• Carbonate deposits, formed from overlaid red algae and calcium carbonate in cell walls, play a global role in carbon storage.
• Deepest photosynthetic eukaryotes, potentially found over 210 meters deep (Bahamas).
• Some show parasitic tendencies on macroalgae (including other red algae).
• 6,000 species; predominantly marine (97%), with smaller freshwater (3%) and subaerial (<1%) populations.
• Identified by bright pink pigments, phycoerythrin and phycocyanin.
• Phycoerythrin efficient light harvester (blue and green light, subtidal zones).
• Freshwater red algae often exhibits bluish coloration due to higher levels of phycocyanin
• Rhodophyta in high light conditions display a spectrum of colors like yellow, violet, brown, or black from photoprotective carotenoid pigments.

Batrachospermum sp.

• Found in clear, cold, flowing freshwater streams.
• Deep water algal species are dark violet or reddish-brown.
• Shallow water species are olive green.

Thallus of Red Algae

• Thallus of red algae is more delicate compared to brown algae.
• Motile forms are absent.
• Even reproductive cells are non-flagellated.

Thallus Forms (Red Algae)

• Many species exhibit a multicellular, macroscopic thallus in diverse forms.
• Uniaxial: Axis formed by one row of filaments.
• Multiaxial: Axis formed by more than one row of filaments.

Cell Wall Structure

• Two main components
• Cellulose fibers (rigid), a glucose polymer.
• Gels of sugar polymers, or polysaccharides (flexible).

Plastids (Rhodophyta)

• Rhodophyta plastids exhibit two general types of morphologies:
• Axial, Stellate: (e.g., Porphyridium) have large plastids with a central paranoid structure.
• Parietal, Discoidal: (e.g., Audouinella) Characterized by multiple, smaller plastids, often lacking paranoids, with Rubisco located between thylakoids.

Storage Products (Red Algae)

• Floridean starch is the storage product.
• Lack amylose (unbranched portion).
• Contains amylopectin (highly branched portion) in alpha-1,4 linkage polymer.

Pit Connections (& Cytokinesis)

• 90% of cells do not completely divide.
• Open regions are eventually plugged with proteins; little evidence for cytoplasmic communication.
• Ordinal level taxonomic character (core & cap morphology).
• Primary pit connections -Open end eventually plugged with proteins, called a primary pit plug (PPP).
• Secondary pit connections- Cytoplasmic connections can be re-established and eventually plugged with proteins and lend strength to filaments.

Reproduction in Red Algae

• Vegetative: Cell division and fragmentation in some multicellular red algae.
• Asexual: Monospores.
• Many taxa primarily utilize vegetative and/or asexual reproduction.

This quiz explores the fundamental differences between prokaryotic and eukaryotic cells, including their structural features and reproductive methods. It also covers the characteristics of algae, highlighting their diversity and unique traits as photosynthetic organisms. Test your knowledge on these essential biological concepts!