Chapter 421. Osmoregulation and Osmotic Stress Draw 42.1a. Electrolytes and water move by diffusion and osmosisb. Diffusion: movement of substances from regions of higher conc.-to regions of lower concentrationc. Osmosis: water moves from higher water conc. to lower water conc.-across a selectively permeable membrane in which some solutes cross more easily than othersd. When solutes are randomly distributed throughout solutions on boths ides of the membrane-an equilibrium is establishede. conc. of dissolved substances in a solution-is the solution's osmolarity2. Osmotic Stressa. Occurs when conc. of dissolved substances in a cell or tissue is abnormalb. Organisms respond to osmotic stress by osmoregulating-process by which organisms control conc. of water and salt in their bodiesc. Sea water nearly matches the normal electrolyte conc. found in sea animalsd. Isotonic: solute conc. inside and outside animal is equale. Osmoconformers: their set point for water and electrolyte conc.-closely matches their environment3. Osmotic Stress in Seawatera. Most fish are osmoregulators: they regulate osmolarity inside their bodies-to achieve homeostasisb. fish osmoregulate bec. their tissues are hypotonic-the solution inside the body has fewer solutes than the solution insidec. When fish drink or breathe excess electrolytes build up-so they actively pump ions out of their bodies using membrane proteins in gill epithelium4. Osmotic Stress in Freshwatera. Marine fish under osmotic stress bec. they lose water and gain salt-freshwater animals under osmotic stress be. they gain water and lose saltb. To achieve homeostasis freshwater fish excrete large amounts of water-in their urine and do not drinkc. Freshwater animals replace electrolytes lost by obtaining them in food or from the water5. Osmotic Stress on Landa. Land animals lose water to the environment through evaporation-there is trade-off bet. breathing water and electrolyte balanceb. water balance complicated bec. all land animals lose water in urine-and some lose water when they sweat or pant to lower their body temp.6. How Do Cells Move Electrolytes and Watera. Solutes move across membranes by passive or active transportb. Passive Transport: driven by diffusion along elecrochemical gradient-and doesnt req. use of ATPc. Active transport: occurs when ATP powers the movement of a solute against its electrochemicalgradientd. Passive Transport often occurs through channels-proteins that form a pore that selectively admits specific ions-also occurs via carries: transmembrane proteins that bind a specific ion-or molecules and transport it across membrane by conformation changee. When solute moves via channels or carriers, facilitated diffusion occurs7. Pumps and Transporta. Active transport: based on membrane proteins called pumps-which change conformation when they bind to ATP or are phosphorylatedb. Sodium-potassium pump is most imp. type of pump in animalsc. Cotransporters can use energy released when an ion-is transported along that electrochemical gradient -to transport a diff. solute against its electrochemical gradientd. Cells use pumps to transport ions and set up an osmotic gradient-in order to transport water across membranes1. Water and Electrolyte Balance in Aquatic Environmentsa. Salt excretion mechanisms of sharksb. Salt-secreting mechanism in sharks exists in many species-including humans (in our kidneys)c. Plant and animals cells use active transport to set up-a strong electrochemical gradient for one ion-usually sodium in animals and Hydrogen in plants2. How Do Sharks Excrete Salta. The rectal gland secretes a concentrated salt solutionb. salt excretion required ATPc. ions can be concentrated only if they are-actively transported against a conc. gradient3. The Role of Sodium/Potassium ATPasea. Biologists hypothesized that the sodium-potassium pump-is involved in salt excretion by sharksb. Tested this by using plant defense compound ouabain-toxic bec. it binds to Na/K ATPase and prevents it from functioningc. rectal glands treated w. ouabain stopped producing a conc. salt solution-so NA/K ATPase is essential for salt excretion4. A Molecular Model For Salt Excretiona. Draw from figure 42.65. Common Molecular Mechanisms Underlies Many Instances of Salt Excretiona. Marine birds and reptiles that drink salt water-excrete NaCL from glands in their nostrilsb. Marine fish excrete salt from their gillsc. Mammals transport salt in their kidneys6. Cystic Fibrosisa. Human protein called cystic fibrosis Transmembrane Regulator (CFTR)b. cystic fibrosis most common genetic disease in ppl descended from N. Europec. CFTR is involved in CL- transport-cystic fibrois results from defect in a chloride channel7. How Do Freshwater Fish Osmoregulatea. Freshwater fish lose electrolytes across their gill epithelium-by diffusion across a conc. gradientb. They actively transport ions into the body across the gill epithelium-in order to maintain homeostasis8. Salmon and Se Bass As Model Systems Draw 42.6a. Salmon individuals move bet. salt water and fresh water-in order to control electrolyte gainb. marine fish have specialized cells in gill epithelium-called chloride cells which move salt using membrane proteins9. Freshwater Chloride Cella. There is a freshwater version of the classical chloride cell-instead of excreting salt these cells import itb. Osmoregularity cells may be in diff. locations-when the nature of osmotic stress changes, the nature of the gill epithelium changesc. There is evidence that diff. forms diff forms of the Na/K ATPase are activated-when individuals are in salt water versus freshwaterd. when fish in seawater, the transporter protein is located-in the basolateral side of chloride cells-when individuals in freshwater the protein is located in the apical side1. How Insects Minimize Water Loss From Body Surfacea. In insects in dry climates, gas exchange occurs across membranes of epithelial cells-that line the tracheae: an extensive system of tubesb. Insect tracheal system connects w. atmosphere at openings called spiracles-muscles inside spiracle or close the porec. Closing spiracles prevents water loss during respirationd. Exoskeleton in insect called cuticle Draw 42.8-consists of chitin and layers of proteine. Chitin has hydrophobic wax layer to prevent water loss2. Types of Nitrogenous Wastesa. excess amino acids and nucleic acids in a cell are broken down into ammoniab. Ammonia is toxic to cells bec. at high conc. it
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