DOMAIN BACTERIA AND DOMAIN ARCHAEA BIOL 1110

What diversity do prokaryotes display in size and shape?

A1. Prokaryotes vary widely:

• Shapes: Cocci (spherical), bacilli (rod-shaped), spirilla (spiral).

• Size: Typically 0.5–5 µm — much smaller than eukaryotic cells.

• Despite simplicity, they show enormous morphological and metabolic diversity.

Q2. How is the prokaryotic cell wall unique in structure and function compared to eukaryotes?

A2.

• Provides shape, protection, and prevents bursting in hypotonic environments.

• Bacteria: Have peptidoglycan (sugar–peptide polymer).

  • Gram-positive: Thick layer.

  • Gram-negative: Thin layer + outer membrane (lipopolysaccharides).

• Archaea: Lack peptidoglycan; have pseudopeptidoglycan or protein walls.

Q3. How is the internal organization of prokaryotes different from that of eukaryotes?

A3.

• No membrane-bound organelles or nucleus.

• DNA in a nucleoid (single circular chromosome).

• May have plasmids (small DNA rings).

• Ribosomes present but smaller (70S).

• Specialized membranes may perform metabolic functions (e.g., photosynthesis, respiration).

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Q4. How can prokaryotes exist in populations of immense size?

A4.

• Rapid reproduction by binary fission (every 1–3 hours).

• Small size allows quick nutrient uptake.

• Mutations accumulate rapidly, generating diversity.

• Can form endospores to survive harsh conditions.

Q5. What are the four major modes of nutrition in prokaryotes?

Mode	Energy Source	Carbon Source	Example

Photoautotroph

Light

CO₂

Cyanobacteria

Chemoautotroph

Inorganic chemicals

CO₂

Nitrosomonas

Photoheterotroph

Light

Organic compounds

Rhodobacter

Chemoheterotroph

Organic compounds

Organic compounds

Most bacteria, animals

How do prokaryotes differ in their oxygen requirements?

Type	Description	Example
Obligate aerobes	Require O₂ for respiration	Mycobacterium
Obligate anaerobes	Poisoned by O₂; use fermentation or anaerobic respiration	Clostridium
Facultative anaerobes	Can use O₂ when available, but survive without it	E. coli

Which organisms perform nitrogen fixation, and why is it vital?

• Certain prokaryotes (e.g., Cyanobacteria, Rhizobium) convert N₂ → NH₃.

• Provides usable nitrogen for plants and other organisms — essential for amino acids & nucleotides

Q8. Describe three examples of metabolic cooperation between prokaryotes.

• Biofilms: Communities of bacteria sharing nutrients and protection.

• Heterocysts: Specialized cells in cyanobacteria for nitrogen fixation.

• Sulfur bacteria & heterotrophs: Exchange nutrients in sediments.

Q9. What are unique features of organisms in Domain Archaea?

• No peptidoglycan in cell walls.

• Membrane lipids have branched hydrocarbons.

• Extreme environments:

  • Thermophiles: Hot springs.

  • Halophiles: High salt.

  • Methanogens: Anaerobic, produce methane.

• Genetic machinery (RNA polymerases, ribosomes) resemble Eukarya more than Bacteria.

Q10. What roles do bacteria play in the biosphere?

• Decomposers: Break down dead matter, recycle nutrients.

• Nitrogen fixation: Convert N₂ → usable nitrogen.

• Producers: Photosynthetic bacteria form base of food chains.

• Symbionts: Live in mutualistic relationships (e.g., gut bacteria).

Q11. How do bacteria impact humans?

A11.
Beneficial:

• Aid digestion, synthesize vitamins.

• Used in biotechnology, food production (yogurt, cheese), and bioremediation.
  Harmful:

• Cause diseases (e.g., tuberculosis, strep throat).

• Some release toxins (endotoxins/exotoxins).

• Antibiotic resistance is an increasing concern.