BSCI207 Water and Solute Regulation I II WATER AND SOLUTE REGULATION I Properties of Water Hydrogen bonds polar interactions as opposite charges attract o Adhesion Water adheres to tissues and forms a lubricating film on body biological membranes o Cohesion Water molecules are attracted to each other by hydrogen bonds and this is the basis for the surface tension and thermal stability of water Results in two important properties o Surface Tension The ability of molecules of a substance which are at the surface to form intermolecular bonds which binds them together o Capillary Action the ability of a liquid to flow against gravity where liquid spontaneously rises in a narrow space High Boiling point high specific heat o It stays liquid at temperatures compatible with life o Essential for cooling via evaporation Ex sweating and panting Good solvent for other polar molecules o Ex NaCl Forces non polar molecules to adhere together in an organized structure It ionizes or dissociates High permeability Transmembrane channel forming glycoproteins Many cells have water channels Aquaporins o 1995 Peter Agre Osmosis concentration The movement of water from areas of higher water concentration to areas of lower water concentration Water moves from a region of low solute concentration to a region of high solute NOTE dissolved substances are separated by a selectively permeable membrane and the solutes cannot cross that membrane Osmolarity 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 mM Osmotic pressure in Osmolar OsM RT C R gas constant C concentration gradient of non permeable solute molecules T temperature K 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 solution o 1mMCaCl2 3OsM solution Tonicity of a Solution o Cell plasma membranes are freely permeable to water but not to most solutes Na K Cl sugars etc If your cells have a of 300 mOsm what is the tonicity of the following solutions What about 300 mM of a permeable solute 200 mM glucose 200 mM NaCl 150 mM NaCl 100mM CaCl2 300 mM sucrose 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 volume o Cytoplasm osmotic pressure o Cytoplasm Ions and other molecules Basic Water Ion Balance Problems Aquatic water gain must accumulate solute Terrestrial water loss must gain Na 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 ions o Contractile vacuoles In sea water o Pump out salt o Prevent water leakage through membrane o Folliculina marine ciliate Important concept In unicellular organisms control of water and ion balance residues in the plasma membrane WATER AND SOLUTE REGULATION II Multicellular Strategies Overview Osmoregulation marine o Relative concentrations of water and solutes must be maintained in a variety of environments land fresh water Excretion o Metabolism creates waste that must be expelled from the body o Proteins and nucleic acids present a problem because ammonia primary waste product is toxic Advantage 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 Osmoregulator Osmoregulation Balancing the uptake and loss of water and solutes over time If they don t osmosis will cause animal cells to swell and burst or shrivel and die o Isoosomotic two solutions with the same osmolarity o Hyperosmotic solution with the greater concentration of solutes o 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 of solutes inside their cells o Internal body fluid is equal to that of the environment but do regulate solutes ions o 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 homeostasis o Internal is regulated independent of the environment o Must pump water and or solutes How do Osmoconformers adjust the of the body fluids Add or subtract solute molecules from the body fluids They adjustable solute molecules must be non toxic and minimally interactive with proteins o Ex many invertebrates use amino acids and derivative What is the Osmoregulator doing to maintain a constant Stenohaline unable to withstand a wide range of salinity o Most animals cannot tolerate substantial changes in external osmolarity Euryhaline can tolerate a wide range of salinity o Animals that can survive large fluctuations in external osmolarity Marine Animals Seawater Most marine invertebrates are osmoconformers Marine vertebrates and some invertebrates are osmoregulators o Ocean is strongly dehydrating because it is much saltier than internal fluids and water is lost by osmosis o Balance water loss by drinking large amounts of seawater o Salt is actively pumped out of gills and passed through urine Saltwater Osmoregulators body fluids tend to concentrate o Problems Gain salt from water Lose water via osmosis o Strategies Minimize water diffusion Pump out salt Freshwater Animals Problems are opposite those of marine animals Freshwater animals are constantly gaining water by osmosis and losing salt by diffusion Maintain water balance by excreting large amounts of very dilute urine and taking in salt by the gills Freshwater Osmoregulators body fluids tend to dilute o Problems Gain water Lose salt via diffusion o Strategies Pump in salt Minimize water diffusion A Salmon Anadromous fish Young slamon in freshwater electrolytes in Young salmon in seawater electroylytes out B Sharks They are isotonic to seawater Shark blood isotonic to seawater urea TMAO ions o Prevents the loss of water However certain concentrations of electrolytes Na K and Cl are much less in sharks than in seawater How do sharks excrete salt o Rectal gland The point is to excrete salt from the body
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