Prokaryotes vs. Eukaryotes Quiz

Prokaryotes vs. Eukaryotes

• Prokaryotic cells (bacteria and archaea) lack a true nucleus and membrane-bound organelles.
• DNA is in a nucleoid region and typically a single circular chromosome.
• Generally smaller and simpler, often single-celled.
• Eukaryotic cells (animals, plants, fungi, and protists) have a defined nucleus with a nuclear membrane.
• DNA is organized into linear chromosomes.
• Possess many membrane-bound organelles (mitochondria, endoplasmic reticulum, Golgi apparatus) for compartmentalized functions.
• Generally larger and can be single-celled or multicellular.

Cyanobacteria - Photosynthetic Prokaryotes

• Among the most diverse groups of bacteria on Earth.
• Seemingly simple cell structure.
• Can be chain-forming or unicellular.
• Important nitrogen fixers, contributing to ocean productivity and nutrient cycling (crucial in nutrient-poor regions).
• Plant chloroplasts likely evolved from cyanobacteria (endosymbiosis theory).
• Essential in Earth's history, fundamental to oxygenation.

Cyanobacteria Morphology and Structure

• Unicellular or filamentous (trichomes).
• Typically have a cell wall (layered).
• Lacks organelles.
• DNA is in circular fibrils.
• Thylakoids and phycobilisomes crucial for photosynthesis.
• No flagella.
• Can exist in diverse environments (including stromatolites).

Cyanobacteria Pigments and Photosynthesis

• Major light-harvesting pigment is chlorophyll a.
• Absorbs red light.
• Also contain carotenoids (e.g., beta-carotene).
• Phycobiliproteins (like phycocyanin and phycoerythrin) change concentration based on light quality and quantity; form phycobilisomes.
• Can perform photosynthesis in aerobic and anaerobic conditions.

Nitrogen Fixation by Cyanobacteria

• Diazotrophs fix atmospheric nitrogen (N2).
• Nitrogenase is responsible, but sensitive to oxygen.
• Photosynthesis occurs during the day, and significant nitrogen fixation often occurs at night to separate the two processes.

Cyanobacteria Habitats and Ecology

• Found in oceans, freshwater, and terrestrial environments (including hot springs, extreme environments etc.)
• Essential components of several extreme environments such as oceans, hot springs, salt marshes, etc.
• Bloom formers in some regions especially during late summer.
• Primary colonisers.
• Crucial in many symbiotic relationships (lichens, root nodules).

Diversity of Marine Cyanobacteria

• Open ocean: picophytoplankton (e.g., Synechococcus, Prochlorococcus).
• Filamentous: Trichodesmium.
• Littoral zones: encrusting or biofilm-forming species.
• Importance to stromatolites and beachrock formation.
• Different colours (e.g., black & pink types) are adapted to different conditions. This is indicated by their desiccation capacity, response to high and low tide environments.

Intertidal Cyanobacteria

• Desiccation (water removal) is a significant issue.
• Cyanobacteria mats are poikilohydric (can withstand desiccation by entering a dormant state).
• Pink biofilm holds water better than the black biofilm and thus are better suited for the intertidal zones and have better desiccation tolerance.