BIOL 1082 Lecture Notes - Lecture 32: Tonicity, Osmotic Concentration, Osmosis
Ch. 50- LO 1
Osmotic regulation Textbook Reading: Sections 50.1-50.6
1. Distinguish among the approaches used by osmoconformers and osmoregulators, listing
examples of each.
• Osmoconformers: to be isosmotic with its surroundings.
o Because the osmolarity is the same as it's environment, there is no tendency to
gain or lose water. Most of these animals live in a stable environment and hence
have a constant osmolarity.
o Sharks, fish
o Allo their od’s osolarit to ofor to the eiroet
• Osmoregulator: to control internal osmolality independent of that of the external
environment.
o Animals that fall under this category live in environments that are inhabitable by
Osmoconformers such as fresh water and terrestrial habitats. They also can
move between fresh water and marine environment.
o Mammals
o Expends energy to control water uptake and loss in a hyper/hypoosmotic
environment
o Atiel regulate od’s osolarit to aitai it so it is ostat
• To live and survive in a hypoosmotic environment, an osmoregulation must discharge
excess water.
• In a hyperosmotic environment, the animal must take in water to offset the osmotic
loss.
2. Compare and contrast osmotic challenges faced by animals in freshwater, marine, and
terrestrial environments, and the adaptations used to address them.
• Freshwater
o Freshwater animals have body fluids that are hyperosmotic because animals
cannot tolerate salt concentrations as low as the freshwater. Thus, they have a
problem with gaining water by osmosis and losing salts by diffusion.
• Marine
o Most marine (invertebrate) animals are osmoconformers. The osmolality is as
the same as the water. Thus, they don't face any challenges in water balance.
o However, because these animals differ considerably from seawater in the
concentrations of specific solutes, they must actively transport solutes to
maintain their homeostasis.
o Osmoregulator marine animals (usually marine vertebrates) constantly lose
water. Due to high salt concentrations in salt water environments.
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o Thus, the water is very dehydrating. To balance the water loss by drinking large
amounts of seawater, they eliminate the ingested salts through their gills and
kidneys.
• Terrestrial
o Adaptations that reduce water loss are key to the survivals of animals that live
on land. The body coverings of animas help prevent dehydration.
o Many terrestrial animals are nocturnal, which reduced the evaporative water
loss because of the lower temperature and higher humidity of night air.
o Land animals maintain water balance by drinking and eating moist food and by
producing water metabolically through cellular respiration.
o Desert animals, such as camels have adapted and can survive to minimize water
loss and survive long periods of time without drinking.
3. Describe the different kinds of nitrogenous waste, their relative toxicity and solubility, and list
which animals excrete each of them.
• Ammonia
o Animals that excrete nitrogenous waste as ammonia need access to lots of water
because ammonia can only be tolerated at very low concentration. If there was a
high concentration of ammonia this can affect the animal in a negative way.
o Thus, ammonia excretion is most common in aquatic species. In most
invertebrates, ammonia release occurs across the whole-body surface.
• Uric Acid
o Insects, lands snails and reptiles including birds excrete uric acid.
Uric acids is nontoxic and does radially dissolve in water.
o Thus, it can be excreted as semisolid and with very little water loss. However,
Uric acids uses more energy than Urea.
• Urea
o Since ammonia is toxic and can only be tolerated when water is constantly and
largely available. Many land animals don't have this much excess to water.
Instead the excrete urea. Urea is the product of metabolic cycle that combines
ammonia with carbon dioxide in the liver.
o Urea is very low in regard to toxicity. However, to produce Urea it takes a lot of
energy.
o Animals that excrete urea would be mammals, most amphibians, sharks and
some bony fish.
o Amphibians excrete mainly ammonia when they are aquatic tadpole and switch
largely to urea excretion when they become land-dwelling animals.
4. Compare and contrast the structure and function of the osmoregulatory organs of flatworms,
earthworms, and insects, detailing where and how the processes of filtration, reabsorption,
secretion, and excretion occur.
• The excretory systems of flatworms consist of units called protonephridia, which form a
network of dead-end tubules.
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Document Summary
Osmoconformers such as fresh water and terrestrial habitats. Thus, they have a problem with gaining water by osmosis and losing salts by diffusion: marine, most marine (invertebrate) animals are osmoconformers. The osmolality is as the same as the water. Due to high salt concentrations in salt water environments. To balance the water loss by drinking large amounts of seawater, they eliminate the ingested salts through their gills and kidneys: terrestrial, adaptations that reduce water loss are key to the survivals of animals that live on land. If there was a high concentration of ammonia this can affect the animal in a negative way. Thus, ammonia excretion is most common in aquatic species. In most invertebrates, ammonia release occurs across the whole-body surface: uric acid. Insects, lands snails and reptiles including birds excrete uric acid. Uric acids is nontoxic and does radially dissolve in water: thus, it can be excreted as semisolid and with very little water loss.
