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Water and Electrolyte Balance in Animals
- Life-sustaining chemical reactions occur in aqueous solutions.
- Disruption in water and solute balance can halt these reactions.
- Water Balance: Achieved when water intake equals water loss, a key aspect of homeostasis.
- Electrolytes: Dissociate into ions in water and are crucial for maintaining electrical and osmotic balance.
- Examples: Na⁺, Cl⁻, K⁺, Ca²⁺.
- Imbalances can cause muscle spasms, fatigue, irregular heart rhythms, or death.
Water Loss and Replacement in Terrestrial Animals
- Terrestrial animals lose water via breathing, defecation, urination, and sometimes sweating.
- Methods to replace water:
- Drinking.
- Absorbing water from food.
- Producing metabolic water during cellular respiration.
Osmoregulation Across Habitats
- Marine Animals:
- Marine bony fishes live in a hyperosmotic environment (seawater has higher solute concentration).
- Challenges: Water loss via osmosis and salt gain via diffusion.
- Adaptations:
- Drink seawater.
- Excrete excess salts via gills and small quantities of concentrated urine.
- Freshwater Animals:
- Freshwater is hyposmotic to their tissues (water moves in, salts move out).
- Challenges: Water gain and electrolyte loss.
- Adaptations:
- Excrete large amounts of dilute urine.
- Actively absorb salts through gills or from food.
- Terrestrial Animals:
- Constant water loss through evaporation, urine, and feces.
- Adaptations:
- Minimize water loss using specialized structures like kidneys.
- Replace lost water through drinking, food, and metabolic processes.
Key Mechanisms for Osmoregulation
- Diffusion: Passive movement of solutes along a gradient.
- Osmosis: Water moves across semipermeable membranes to balance solute concentrations.
- Active Transport:
- Primary (e.g., Na⁺/K⁺ pump).
- Secondary (uses established gradients, e.g., symporters and antiporters).
- Water movement: No active transport; follows osmotic gradients via aquaporins.
Osmoconformers vs. Osmoregulators
- Osmoconformers: Marine invertebrates (e.g., jellyfish) match their internal osmolarity to the environment.
Teacher: System Administrator
