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Explain the cell wall, plasma membrane and cytoplasm of a prokaryotic cell.

GeneralClass 12AllAnswered 27 Mar 2026
Answer

Cell Wall and Plasma Membrane

Cell Wall:

  • Rigid structure providing shape and protection
  • Composition: Peptidoglycan (NAG-NAM polymer cross-linked by peptides)
  • Types:
    • Gram-positive: Thick peptidoglycan (stains purple)
    • Gram-negative: Thin peptidoglycan + outer lipopolysaccharide membrane (stains pink)
  • Functions:
    • Prevents osmotic lysis
    • Provides structural support
    • Pathogen recognition target

Plasma Membrane:

  • Phospholipid bilayer with proteins (similar to eukaryotes)
  • Selectively permeable – controls material exchange
  • Functions:
    • Respiration (electron transport chain embedded)
    • Photosynthesis (in cyanobacteria via chromatophores)
    • DNA replication site attachment

(2) Cytoplasm

  • Fluid matrix containing:
    • 70S ribosomes (protein synthesis)
    • Nucleoid (genetic material)
    • Plasmids (extra-chromosomal DNA)
    • Inclusion bodies (storage granules)
    • Mesosomes (membrane extensions – respiratory and replication sites)
  • Lacks membrane-bound organelles (no mitochondria, ER, Golgi, etc.)

Adaptation: Simple organization allows rapid reproduction and metabolic flexibility.

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