Chapter 42 1 Osmoregulation and Osmotic Stress Draw 42 1 a Electrolytes and water move by diffusion and osmosis b Diffusion movement of substances from regions of higher conc to regions of lower concentration c Osmosis water moves from higher water conc to lower water conc across a selectively permeable membrane in which some solutes cross more easily than others d When solutes are randomly distributed throughout solutions on boths ides of the membrane an equilibrium is established e conc of dissolved substances in a solution is the solution s osmolarity 2 Osmotic Stress a Occurs when conc of dissolved substances in a cell or tissue is abnormal b Organisms respond to osmotic stress by osmoregulating process by which organisms control conc of water and salt in their bodies c Sea water nearly matches the normal electrolyte conc found in sea animals d Isotonic solute conc inside and outside animal is equal e Osmoconformers their set point for water and electrolyte conc closely matches their environment 3 Osmotic Stress in Seawater a Most fish are osmoregulators they regulate osmolarity inside their bodies to achieve homeostasis b fish osmoregulate bec their tissues are hypotonic the solution inside the body has fewer solutes than the solution inside c When fish drink or breathe excess electrolytes build up so they actively pump ions out of their bodies using membrane proteins in gill epithelium 4 Osmotic Stress in Freshwater a Marine fish under osmotic stress bec they lose water and gain salt freshwater animals under osmotic stress be they gain water and lose salt b To achieve homeostasis freshwater fish excrete large amounts of water in their urine and do not drink c Freshwater animals replace electrolytes lost by obtaining them in food or from the water 5 Osmotic Stress on Land a Land animals lose water to the environment through evaporation there is trade off bet breathing water and electrolyte balance b 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 Water a Solutes move across membranes by passive or active transport b Passive Transport driven by diffusion along elecrochemical gradient and doesnt req use of ATP c Active transport occurs when ATP powers the movement of a solute against its electrochemical gradient d 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 change e When solute moves via channels or carriers facilitated diffusion occurs 7 Pumps and Transport a Active transport based on membrane proteins called pumps which change conformation when they bind to ATP or are phosphorylated b Sodium potassium pump is most imp type of pump in animals c Cotransporters can use energy released when an ion is transported along that electrochemical gradient to transport a diff solute against its electrochemical gradient d Cells use pumps to transport ions and set up an osmotic gradient in order to transport water across membranes 1 Water and Electrolyte Balance in Aquatic Environments a Salt excretion mechanisms of sharks b 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 plants 2 How Do Sharks Excrete Salt a The rectal gland secretes a concentrated salt solution b salt excretion required ATP c ions can be concentrated only if they are actively transported against a conc gradient 3 The Role of Sodium Potassium ATPase a Biologists hypothesized that the sodium potassium pump is involved in salt excretion by sharks b Tested this by using plant defense compound ouabain toxic bec it binds to Na K ATPase and prevents it from functioning c rectal glands treated w ouabain stopped producing a conc salt solution so NA K ATPase is essential for salt excretion 4 A Molecular Model For Salt Excretion a Draw from figure 42 6 5 Common Molecular Mechanisms Underlies Many Instances of Salt Excretion a Marine birds and reptiles that drink salt water excrete NaCL from glands in their nostrils b Marine fish excrete salt from their gills c Mammals transport salt in their kidneys 6 Cystic Fibrosis a Human protein called cystic fibrosis Transmembrane Regulator CFTR b cystic fibrosis most common genetic disease in ppl descended from N Europe c CFTR is involved in CL transport cystic fibrois results from defect in a chloride channel 7 How Do Freshwater Fish Osmoregulate a Freshwater fish lose electrolytes across their gill epithelium by diffusion across a conc gradient b They actively transport ions into the body across the gill epithelium in order to maintain homeostasis 8 Salmon and Se Bass As Model Systems Draw 42 6 a Salmon individuals move bet salt water and fresh water in order to control electrolyte gain b marine fish have specialized cells in gill epithelium called chloride cells which move salt using membrane proteins 9 Freshwater Chloride Cell a There is a freshwater version of the classical chloride cell instead of excreting salt these cells import it b Osmoregularity cells may be in diff locations when the nature of osmotic stress changes the nature of the gill epithelium changes c There is evidence that diff forms diff forms of the Na K ATPase are activated when individuals are in salt water versus freshwater d 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 side 1 How Insects Minimize Water Loss From Body Surface a In insects in dry climates gas exchange occurs across membranes of epithelial cells that line the tracheae an extensive system of tubes b Insect tracheal system connects w atmosphere at openings called spiracles muscles inside spiracle or close the pore c Closing spiracles prevents water loss during respiration d Exoskeleton in insect called cuticle Draw 42 8 consists of chitin and layers of protein e Chitin has hydrophobic wax layer to prevent water loss 2 Types of Nitrogenous Wastes a excess amino acids and nucleic acids in a cell are broken down into ammonia b Ammonia is toxic to cells bec at high conc it raises the pH of intracellular and extracelluular fluids
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