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UT BIO 311D - Osmoregulation and Excretion (Part I)
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BIO 311D 1st Edition Lecture 20 Outline of Last Lecture I. Origin of Self-ToleranceII. Proliferation of B Cells and T CellsIII. Immunological MemoryOutline of Current LectureI. Clicker questionsII. OsmoregulationIII. Seawater fishIV. Freshwater fishV. Land AnimalsVI. Transport Epithelia Current Lecture1. All of the following are adaptations of freshwater fish for osmoregulation except:A. Excreting hypotonic urineB. Actively transporting salts out of the blood at the gillsC. Not drinking waterD. Excretion of salt ions and large amounts of water in dilute urine from kidneys*they actively transport salts IN, not out2. An aquatic animal with an internal solute concentration of 500 mOsm/L is placed in a fluid with solute concentration of about 700 mOsm/L. To osmoregulate and survive, the animal must:A. Pump in salts to change its tissues to 700 mOsm/LB. Pump in salts to keep tissues at 600 mOsm/LC. Pump out salts to keep tissues at 500 mOsm/LD. Pump out salts to change its tissues to 900 mOsm/L3. Adaptations of desert animals do not likely includeA. Shells, scales, and thick skinB. A nocturnal activity patternC. Conservation of metabolic waterD. Nitrogenous waste excreted as ammoniaE. The production of concentrated urine*D is wrong because it is excreted as uric acid (more concentrated, you do not lose any excess water)- Fish excrete as ammonia (ammonia is toxic but does not affect environment because water is surrounded and dilutes the ammonia)- Bacteria can break down ammoniaTask: place a fish in seawater1. How would water move by osmosis? - Water would move from the fish to the seawater since seawater is hypertonic compared to the fish2. How would salt move by diffusion? - Salt would move into the fish3. How would the fish correct for the movement of water and salt? - The fish will drink a lot of water to compensate for water loss and transport the salt outOsmoregulation balances the uptake and loss of water and solutes• Osmoregulation is based largely on controlled movement of solutes between internal fluids and the external environmentOsmosis and Osmolarity• Cells require a balance between uptake and loss of water• Osmolarity, the solute concentration of a solution, determines the movement of water across a selectively permeable membrane• If two solutions are isoosmotic, the movement of water is equal in both directions• If two solutions differ in osmolarity, the net flow of water is from the hypoosmotic to thehyperosmotic solution Osmotic Challenges• Osmoconformers, consisting only of some marine animals, are isoosmotic with their surroundings and do not regulate their osmolarity• Osmoregulators expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic environment• Most animals are stenohaline; they cannot tolerate substantial changes in external osmolarity• Euryhaline animals can survive large fluctuations in external osmolaritySaltwater fish:- Water goes out, salt goes in- Compensated by salt goes out and water go in- Most marine invertebrates are osmoconformers- Most marine vertebrates and some invertebrates are osmoregulators- Marine bony fishes are hypoosmotic to seawater- They lose water by osmosis and gain salt by diffusion and from food- They balance water loss by drinking seawater and excreting saltsFreshwater fish:- Water goes in, salt goes out- Compensates by excreting out water, chloride is actively being transported in and sodium follows (allowing salt to go inside)- Freshwater animals constantly take in water by osmosis from their hypoosmotic environment- They lose salts by diffusion and maintain water balance by excreting large amounts of dilute urine- Salts lost by diffusion are replaced in foods and by uptake across the gillsAnimals That Live in Temporary Waters• Some aquatic invertebrates in temporary ponds lose almost all their body water and survive in a dormant state• This adaptation is called anhydrobiosis• Tardigrades are animals that can live without water (they live in ponds but if there is no water they can stay in their dehydrated form)Land Animals• Adaptations to reduce water loss are key to survival on land• Body coverings of most terrestrial animals help prevent dehydration• Desert animals get major water savings from simple anatomical features and behaviors such as a nocturnal lifestyle• Land animals maintain water balance by eating moist food and producing water metabolically through cellular respiration*sole purpose of countercurrent exchange in humans is to remove saltsEnergetics of Osmoregulation• Osmoregulators must expend energy to maintain osmotic gradients• The amount of energy differs based on– How different the animal’s osmolarity is from its surroundings– How easily water and solutes move across the animal’s surface– The work required to pump solutes across the membraneTransport Epithelia in Osmoregulation• Animals regulate the solute content of body fluid that bathes their cells• Transport epithelia are epithelial cells that are specialized for moving solutes in specific directions• They are typically arranged in complex tubular networks• An example is in nasal glands of marine birds, which remove excess sodium chloride from the bloodAn animal’s nitrogenous wastes reflect its phylogeny and habitat• The type and quantity of an animal’s waste products may greatly affect its water balance• Among the most significant wastes are nitrogenous breakdown products of proteins and nucleic acidsSome


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