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What is Osmoregulation?

Nicole Teeter, Elizabeth Friedl
  • Author
    Nicole Teeter

    Nicole is a dedicated high school teacher with 16 years of experience in the classroom teaching AP Biology, biology, and integrated middle school science. She has an M.Ed in Curriculum and Instruction and a B.S in Biology from Penn State University. She holds teaching certifications in mathematics, biology and general science.

  • Instructor
    Elizabeth Friedl

    Elizabeth, a Licensed Massage Therapist, has a Master's in Zoology from North Carolina State, one in GIS from Florida State University, and a Bachelor's in Biology from Eastern Michigan University. She has taught college level Physical Science and Biology.

Discover what osmoregulation is and see a definition. Compare osmoregulators and osmoconformers and understand energetics and osmoregulation in fishes and humans. Updated: 02/23/2022

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Osmoregulation

Every organism operates within a fluid environment, from cells and tissues to organs and organ systems. For these organisms to function properly, water and solutes must be maintained within a narrow margin. This can be challenging for animals due to stress from the external environment. For example, a freshwater organism that lives in an external environment that creates challenges by threatening to flood and dilute body fluids must possess adaptations that reduce water uptake, conserve solutes, and absorb salts from its surroundings. Organisms must utilize the homeostatic process of osmoregulation in order to regulate solute concentrations and balance the gain and loss of water. The kidney is an organism's greatest balancing act. The main role of the kidney is to maintain osmotic balance by regulating water and salts within the body. This is essential for the body to function correctly.

Water enters and leaves an organism through osmosis. Osmosis occurs any time two solutions are separated by a membrane that differ in osmotic pressure, or osmolarity. If two organisms separated by a selectively permeable membrane have the same osmolarity, they are classified as isosmotic. In this instance, there is no net movement of water between the solutions. Water will move at equal rates in both directions. If two solutions differ in osmolarity, the one with the greater concentration of solutes is said to be hyperosmotic and the one that has a lesser concentration of solutes is said to be hyposmotic. Water will flow from the hyposmotic to the hyperosmotic one.

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Osmoconformers

Marine animals can be isosmotic to their surroundings. These animals do not actively adjust their internal osmolarity and are referred to as osmoconformers. Because an osmoconformer is isosmotic (the osmolarity internally is equal to the surrounding environment), there is no need to gain or lose water. These organisms live in water that has a stable composition, therefore allowing them to maintain a constant osmolarity. One example of an osmoconformer is a jellyfish. Jellyfish maintain a body fluid concentration isotonic (equal) to their environment. Osmoconformers, like the jellyfish, have no need to osmoregulate because seawater has a stable composition and closely matches the concentrations found within these marine organisms.


Organisms, like the jellyfish, have no need to osmoregulate. Instead, a jellyfish is an osmoconformer. Osmoconformers are isosmotic to the external environment and have no need to gain or lose water.

jellyfish


Osmoregulators

In contrast to osmoconformers, osmoregulators are animals that need to control their internal osmolarity because their body fluids are not isosmotic with their environment. Osmoregulators must release excess water into the outside environment if they live in a hyposmotic (freshwater) environment, or they need to take in water to offset water loss if they live in a hyperosmotic environment. Osmoregulation enables organisms to live in environments that osmoconformers cannot. Additionally, it allows marine organisms to maintain an osmolarity different from seawater. For example, sharks have an internal salt concentration much lower than that of seawater. As a result, salt diffuses into the shark's body from the seawater across their gills. The shark's kidneys filter the excess salt and excrete it.

Osmoregulation Energetics

Energetics is the study of the amount or type of energy used in a particular process, such as osmoregulation. Any time an animal has to maintain an osmolarity difference between the body and the external environment, there is an energy cost. Diffusion of water and salts will occur to establish equilibrium of the system; however, osmoregulators must expend energy to regulate the osmotic gradients that cause water to flow in and out of the system. Active transport, the process of pumping molecules against the concentration gradient, occurs to manipulate the solute concentrations within the animal's body.

Osmoconformers vs. Osmoregulators

Osmoconformers Osmoregulators
live in environments with very stable compositions not isosmotic to their environment
have a constant internal osmolarity must control their internal osmolarity
no need to gain or lose water discharge water if the animal lives in a hypotonic environment or takes in water if the animal lives in a hypertonic environment
regulates naturally through osmosis and diffusion requires energy to regulate
example: jellyfish example: human

Humans are osmoregulators. If trapped at sea, a human could not drink seawater to survive. The regulation of osmotic pressure is controlled by the kidney. The kidney filters the blood to regulate the concentrations by regulating the amount of water and salts within the blood. Any excess is filtered out and excreted in the urine. Producing excessive amounts of urine is a way to remove excess water while retaining solutes.

Osmoregulators in Freshwater and Seawater

Osmoregulation is essential for an organism to maintain homeostasis. Organisms must balance water in order to survive. More aquatic animals are found in the sea than anywhere else. Most marine animals are osmoconformers; however, some require osmoregulation. Saltwater fish that osmoregulate do so by gaining water and salts from drinking seawater. To osmoregulate, the saltwater fish will filter excess salt ions across the gills and through the kidney. A small amount of water is also excreted.

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Frequently Asked Questions

What are examples of osmoregulators?

Humans are osmoregulators. If trapped at sea, a human could not drink seawater to survive. The regulation of osmotic pressure is controlled by the kidney. The kidney filters the blood in order to remove excess water and solutes, which are excreted as urine.

What is the process of osmoregulation?

Organisms must utilize the homeostatic process of osmoregulation in order to regulate solute concentrations and balance the gain and loss of water. Osmoregulators are animals that must control their internal osmolarity because they are not isosmotic to their environment. These animals must expend energy to regulate their internal environment by either discharging water if the animal lives in a hypotonic environment or taking in water if the animal lives in a hypertonic environment.

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