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BSCI207 – Water and Solute Regulation I & IIWATER AND SOLUTE REGULATION I Properties of Water- Hydrogen bonds – polar interactions as opposite charges attracto Adhesion - Water adheres to tissues and forms a lubricating film on bodybiological membraneso Cohesion - Water molecules are attracted to each other by hydrogen bondsand this is the basis for the surface tension and thermal stability of water- Results in two important propertieso Surface Tension - The ability of molecules of a substance which are at thesurface to form intermolecular bonds which binds them togethero Capillary Action - the ability of a liquid to flow against gravity where liquidspontaneously rises in a narrow space- High Boiling point (high specific heat)o It stays liquid at temperatures compatible with lifeo Essential for cooling via evaporation  Ex. sweating and panting- Good solvent for other polar moleculeso Ex. NaCl- Forces non-polar molecules to adhere together in an organized structure- It ionizes or dissociates- High permeability!Many cells have water channels!- Transmembrane, channel-forming glycoproteins- Aquaporinso 1995 – Peter AgreOsmosis- The movement of water from areas of higher water concentration to areas of lowerwater concentration- Water moves from a region of low solute concentration to a region of high soluteconcentration- NOTE – dissolved substances are separated by a selectively permeable membraneand the solutes cannot cross that membraneOsmolarity vs. Molarity- Osmolarity – the measure of solute concentration; defined as the number of osmoles(Osm) of solute per liter (L) of solution- Osmoles vs. moles- mOsm vs. mMπ =RTΔC- π = Osmotic pressure in Osmolar (OsM)- R = gas constant- T = temperature (K)- ΔC = concentration gradient of non-permeable solute moleculeso Cell plasma membranes are freely permeable to water, but not to most solutes (Na+, K+, Cl-, sugars, etc.)Osmoles and Osmolar- The total number of solute particles (all molecular species) in solution- Thus:o 1 mM glucose = 1mOsM solution*o 1mM NaCl = 2 OsM solutiono 1mMCaCl2 = 3OsM solutionTonicity of a SolutionIf your cells have a π of ~300 mOsm, what is the tonicity of the following solutions?- 200 mM glucose- 200 mM NaCl- 150 mM NaCl- 100mM CaCl2- 300 mM sucrose- What about 300 mM of a permeable solute?Summary- Water is freely permeable to most plasma membranes, solute molecules are not!o NOTE – Water moves most rapidly!- Cells must maintain homeostasis including:o Cell volumeo Cytoplasm osmotic pressureo Cytoplasm [Ions] and other [molecules]Basic Water & Ion Balance Problems- Terrestrial  water loss & must gain Na+-Aquatic  water gain & must accumulate solute(ions)- Marine  water loss & must remove solutes (ions) gained from sea water Single-Celled Organisms- In fresh water …o Pump out water and use membrane ion pumps to accumulate ionso Contractile vacuoles- In sea water …o Pump out salto Prevent water leakage through membraneo Folliculina: marine ciliateImportant concept: In unicellular organisms, control of water and ion balanceresidues in the plasma membrane!WATER AND SOLUTE REGULATION II (Multicellular Strategies)Overview- Osmoregulationo Relative concentrations of water and solutes must be maintained in a variety of environments (land, fresh water,marine)- Excretiono Metabolism creates waste that must be expelled from the bodyo Proteins and nucleic acids present a problem because ammonia (primary waste product) is toxicAdvantage of a body cavity with body fluids separated or isolated from the surrounding water?Body Fluid & Cytoplasm- Body fluids & cytoplasm ~300 mOsM for most vertebrates- Variable for marine vertebrates, protists, and bacteria, but cytoplasm is close to 300 mOsM- Osmoconformer vs. OsmoregulatorOsmoregulation- Balancing the uptake and loss of water and solutes over time. If they don’t osmosis will cause animal cells to swell andburst or shrivel and die.o Isoosomotic = two solutions with the same osmolarityo Hyperosmotic = solution with the greater concentration of soluteso Hyposomotic = solution with the more dilute concentration of solutes- Water flows from a hyposomotic solution to a hyperosmotic one.Multicellular aquatic or marine organisms (TWO BASIC SOLUTIONS)- Osmoconformers – do not actively regulate the osmolarity of their tissues, although they do regulate the composition ofsolutes inside their cellso Internal body fluid π is equal to that of the environment but do regulate solutes & ionso Usually requires formation or loss of non-toxic solute Amino acids, amino acid metabolites, urea, etc.- Osmoregulators – actively regulate osmolarity of their bodies to achieve homeostasiso Internal π is regulated independent of the environmento Must pump water and/or solutes How do Osmoconformers adjust the π of the body fluids?- Add or subtract solute molecules from the body fluids- They adjustable solute molecules must be non-toxic and minimally interactivewith proteinso Ex. many invertebrates use amino acids and derivativeWhat is the Osmoregulator doing to maintain a constant π?- Stenohaline – unable to withstand a wide range of salinityo Most animals cannot tolerate substantial changes in external osmolarity- Euryhaline – can tolerate a wide range of salinityo Animals that can survive large fluctuations in external osmolarity Marine Animals (Seawater)- Most marine invertebrates are osmoconformers- Marine vertebrates and some invertebrates are osmoregulatorso Ocean is strongly dehydrating because it is much saltier than internal fluidsand water is lost by osmosiso Balance water loss by drinking large amounts of seawatero Salt is actively pumped out of gills and passed through urine- Saltwater Osmoregulators: body fluids tend to concentrateo Problems: Gain salt from water Lose water via osmosiso Strategies Pump out salt Minimize water diffusion Freshwater Animals- Problems are opposite those of marine animals- Freshwater animals are constantly gaining water by osmosis and losing salt bydiffusion- Maintain water balance by excreting large amounts of very dilute urine andtaking in salt by the gills- Freshwater Osmoregulators: body fluids tend to diluteo Problems: Gain water Lose salt via diffusiono Strategies: Pump in salt Minimize water diffusion A. Salmon – Anadromous fish- Young slamon in freshwater  electrolytes in- Young salmon in seawater  electroylytes outB. Sharks- They are


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UMD BSCI 207 - Water and Solute Regulation I & II

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