QE REVIEWW

• Osmoregulation


  The processes by which animals control solute concentrations and balance water gain and loss
• Osmoconformers

  • Marine animals whose internal osmolarity is the same as their environment, so they face no substantial changes in water balance
• Osmoregulators


  • Animals that control their internal osmolarity independent of their external environment, enabling them to live in freshwater and terrestrial habitats
• Stenohaline


  Animals that cannot tolerate substantial changes in external osmolarity
• Euryhaline


  Animals that can survive large fluctuations in external osmolarity
• Marine invertebrates

  • Mostly osmoconformers, with internal osmolarity the same as seawater
• Freshwater animals


  • Must be hyperosmotic to their environment, so they face the problem of gaining water by osmosis
• Osmoregulation in freshwater fish

  Excrete large amounts of dilute urine, drink almost no water, and take up salt across gills
• Osmoregulation in migratory fish like salmon

  Undergo dramatic changes when moving between fresh water and seawater, adjusting hormone levels and specialized cells to regulate salt and water balance
• Anhydrobiosis


  • Dormant state of some aquatic invertebrates that can survive extreme dehydration, enabled by adaptations like accumulating sugars to protect cell membranes
• Adaptations of terrestrial animals

  • Body coverings to reduce water loss, nocturnal activity, drinking, eating moist foods, and producing metabolic water
• Camels can tolerate long periods without drinking water
• The body coverings of most terrestrial animals help prevent dehydration
• Examples of body coverings that prevent dehydration

  • Waxy layers of insect exoskeletons
  • Shells of land snails
  • Layers of dead, keratinized skin cells covering most terrestrial vertebrates, including humans
• Nocturnality in many terrestrial animals


  Reduces evaporative water loss due to lower temperature and higher humidity of night air
• Terrestrial animals lose water through a variety of routes: in urine and feces, across the skin, and from the epithelial surfaces of gas exchange organs and airways
• Land animals maintain water balance by

  Drinking and eating moist foods, and producing water metabolically through cellular respiration
• Some desert animals

  • Can survive for long periods without drinking
  • Camels can tolerate a 7°C rise in body temperature, greatly reducing water lost in sweat
• Osmoregulation


  Maintaining an osmolarity difference between an animal's body and its external environment carries an energy cost
• Osmoregulation accounts for 5% or more of the resting metabolic rate for many fishes
• For brine shrimp, the cost of osmoregulation is correspondingly high—as much as 30% of the resting metabolic rate
• Body fluids of most animals adapted to their habitat's salinity

  Freshwater animals have lower solute concentrations than their marine relatives
• How desert mice maintain osmotic homeostasis

  Urine osmolarity increases, blood osmolarity and urea concentration increase, to conserve water
• Transport epithelia


  One or more layers of epithelial cells specialized for moving particular solutes in controlled amounts in specific directions
• Salt glands in marine birds, turtles, and iguanas

  Use active transport to secrete a fluid much saltier than the ocean, enabling a net gain of water
• Ammonia


  Very toxic, can interfere with oxidative phosphorylation, requires lots of water for excretion
• Urea

  Less toxic than ammonia, more soluble, but energetically expensive to produce
• Uric acid


  Relatively nontoxic, insoluble, can be excreted with little water loss, but also energetically expensive
• Aquatic animals, including most bony fishes, excrete mainly ammonia
• Birds, many reptiles, insects, and land snails excrete mainly uric acid
• Mammals, most amphibians, sharks, and some bony fishes excrete mainly urea
• An animal's nitrogenous wastes

  Reflect its phylogeny and habitat
• Terrestrial turtles excrete mainly uric acid, while aquatic turtles excrete both urea and ammonia
• Amphibian embryos can excrete ammonia or urea, which can diffuse out of the egg, while bird and reptile embryos excrete uric acid, which is trapped in the egg
• The amount of nitrogenous waste produced is coupled to the animal's energy budget and diet
• Ammonia


  Nitrogenous waste product excreted mainly by amphibians
• Urea

  Nitrogenous waste product excreted largely by amphibians as adults
• Uric acid


  Nitrogenous waste product excreted as a harmless solid by reptiles, birds, and some mammals
• The amount of nitrogenous waste produced is coupled to the animal's energy budget
• Predators, which derive much of their energy from protein, excrete more nitrogen than animals that rely mainly on lipids or carbohydrates