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Explain the following vacuoles: (a) Sap vacuoles (b) Contractile vacuoles (c) Food vacuoles

GeneralClass 12AllAnswered 27 Mar 2026
Answer

(a) Sap Vacuoles (Plant Vacuoles)

  • Structure: Large, membrane-bound (tonoplast) organelle occupying up to 90% of cell volume
  • Contents (Cell sap):
    • Water (main component)
    • Mineral salts (K⁺, Na⁺, Cl⁻, NO₃⁻)
    • Sugars, amino acids
    • Organic acids (malic, citric)
    • Pigments (anthocyanins – flower colors)
    • Secondary metabolites (tannins, alkaloids)
  • Functions:
    • Storage: Nutrients, metabolites, waste products
    • Turgor pressure: Cell rigidity, plant support
    • Hydrolysis: Digestive enzymes (similar to lysosomes)
    • pH regulation: Maintain acidic pH (3–5)

(b) Contractile Vacuoles (Osmoregulatory Vacuoles)

  • Occurrence: Freshwater protozoans (Amoeba, Paramecium, Euglena)
  • Structure: Star-shaped central vacuole with radiating canals
  • Mechanism:
    • Collects excess water entering cell by osmosis
    • Periodically contracts, expelling water through pore
    • Prevents osmotic lysis in hypotonic environment
  • Functions:
    • Osmoregulation: Water balance maintenance
    • Excretion: Removal of nitrogenous wastes

Frequency: Contracts every 10–60 seconds depending on osmotic pressure

(c) Food Vacuoles (Phagosomes)

  • Occurrence: Protozoans, phagocytic cells (macrophages, neutrophils)
  • Formation: By endocytosis:
    • Cell membrane invaginates around food particle
    • Forms phagosome (food vacuole)
    • Fuses with lysosome → phagolysosome
  • Function: Intracellular digestion
    • Lysosomal enzymes digest food
    • Nutrients absorbed into cytoplasm
    • Residual body expelled by exocytosis

Example: Amoeba engulfs bacteria via pseudopodia forming food vacuole

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General · Class 12