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Osmoregulation in Aquatic Invertebrates - Coggle Diagram

- - - - Saline waters
        
        Brackish Water
        
        • Formed when fresh-water mixes with sea water in coastal regions
        
        • Salinity ranges from 3.0% to 0.05%
        
        • Forms a transition zone between fresh-water and marine habitats
        
        High Salt Content in Inland Waters
        
        • The Dead Sea in Israel is saturated
        
        o Chloride and magnesium are the major ions
        
        o Crystallising calcium sulphate
        
        o Harbours no plants and animals, only microorganisms
        
        • Note:
        o Salt solution has different composition in both water bodies
        
        • The Great Salt Lake in Utah
        
        o Sodium chloride is predominant
        
        o Crystallises out on shores
        
        o No fish, only some organisms survive e.g. Artemia (brine shrimp)
        
        Surface Coverage:
        • Covers less than 1% of Earth’s surface
        
        Saline Springs
        
        • Some springs have unusual and relatively high salt contents
        • Offer minor importance or significance compared to larger water bodies
        
        Importance:
        
        • Acts as a barrier for distribution of:
        
        o Fresh-water animals (one side)
        o Marine animals (other side)
        
        • Extreme physiological importance
      - Units
        
        Molarity (M)
        
        • Moles of solute dissolved per litre of solution
        
        • Unit of concentration of dissolved substance
        
        • mmol (millimole) used more often in biological context
        
        Osmolarity
        
        • Osmoles per litre
        
        • Expression of the osmotic concentration of a solution
        
        • Determined by number of dissolved particles
        
        • Independent of specific solutes
        
        Non-Electrolytes:
        
        • e.g. Urea, sucrose
        • Osmolarity = Molarity (no dissociation)
        
        Electrolytes:
        
        • Ionic dissociation in solution
        • Osmolarity is higher than molarity
        
        Isotonic vs Iso-osmotic
        
        Isotonic:
        
        • Describes behaviour of cells in a solution
        
        • Cell does not shrink or swell
        
        • Retains original volume, shape, size
        
        Iso-osmotic:
        
        Iso-osmotic:
        
        • Defines physical chemistry
        
        • Living cells may swell and burst in an osmotic solution
- - - - Reduce passive water and ion movement.
        No animal is completely impermeable.
    - - Hypotonic urine production to conserve solutes.
    - - Carcinus shows increased oxygen
        consumption in diluted water.
        Eriocheir (mitten crab) maintains constant
        metabolic rate across salinities.
  - - - Examples:
      - Anodonta (freshwater clam): ~50 mOsm/L.
      - Potamobius (crayfish): ~500 mOsm/L.
  - - - Live in transitional zones between freshwater and marine environments.
      - Salinity ranges: 0.05% to 3.0%.
      - Physiologically significant due to fluctuating salinity.
      - Osmoregulatory strategies mimic freshwater animals but at different concentration levels.
- - - - regulatory mechanisms
        
        kidney
        
        malpighian tubules
        
        maintains suplhate concentration
        
        heavy substances: calcium phosphate and calcium carbonate
        
        swimming coelenterate: devoid to reduce body weight
        
        magnesium (depresses neuromuscular contractions)
        
        fast moving animals: low magnesium levels
        
        slow moving animal: high magnesium levels
    - - Intracellular vs. Extracellular Ion Distribution
        
        Sodium (Na⁺) and potassium (K⁺) concentrations are different inside and outside cells.
        Despite this, cells remain iso-osmotic (same total solute concentration) with blood/tissue fluids.
      - Free Amino Acids as Osmolytes
        
        Cells adjust their free amino acid concentration to respond to salinity changes:
        
        High salinity: amino acids accumulate to retain water.
        
        Low salinity: amino acids decrease to release water.
        
        This maintains osmotic balance without affecting enzyme activity.
      - Protein Turnover in Osmotic Regulation
        
        Protein degradation increases intracellular amino acids.
        
        Protein synthesis reduces amino acid concentration.
        
        These processes regulate osmotic pressure without relying heavily on inorganic ions (which can disrupt enzyme function).
      - Selective Amino Acid Usage
        
        Amino acids like lysine and arginine: avoided due to their strong impact on enzyme activity.
        
        Amino acids like β-alanine, serine, glycine: high in concentration, minimal effect on enzyme kinetics.
        
        Membrane Permeability and Water Movement
        
        In low salinity, water enters the cell, distending it.
        
        To recover:
        
        Amino acids exit the cell,
        
        Water follows osmotically,
        
        Volume is restored.
    - - Osmoconformers
        
        No problem with osmotic water movement
        
        Eliminates a major physiological challenge for aquatic organisms
        
        Body fluid osmotic concentration is equivalent to seawater
        
        Maintain salt concentrations that are out of equilibrium with the external medium
        
        Being osmoconformers does not mean identical ion composition
        
        Body fluid solute composition differs from seawater
- - - - Active transport: Movment of ions across membranes against cincentration gradient
      - Specialised organs: Anal gills & crustacean gills
      - ATP-dependent, requires energy
      - E.g.: Carcinus, Eriocheir
    - - Higher permeable body surfaces
      - Solue concentration inside animal is higher