Study Guide for Chapter 51

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Biological Sciences
Mary Olaveson

Chapter 51 Salt and Water Balance and Nitrogen Excretion Excretory organs- controls the volume, concentration and composition of the extra cellular fluids of animals. -the concentration of solutes in an animals extra cellular fluid determines the water balance of its cells, and the composition of the extra cellular fluid influences the health and function of the cell it bathes. -if solute concentrations are different on two sides of a membrane permeable to water but not to the solutes, the water will flow form the side with the lower concentration to the side with the higher concentration of solute. -if solute concentrations in the extra cellular fluid surrounding the animal cells is less than in the cells cytoplasm, than water will move into the cells to possibly swell up and burst. Osmosis- the movement of water across a membrane Osmolarity- of a solution is the number of moles of osmotic ally active solutes per liter of solvent. -Excretory organs control the osmolarity and the volume of the extra cellular fluids (blood and interstitial fluid) by excreting solutes that are present in excess (like NaCl when we eat salty foods) and conserving solutes that are valuable or in short supply (such as glucose and amino acids) -The output of the excretory organs is called urine -No active transport of water in excretory systems, water must be moved either by a pressure difference or by a difference in osmolarity Osmoconformers- marine invertebrates equilibrate their extra cellular fluid osmolarity with the ocean water Osmoregulators- other marine animals maintain extra cellular fluid osmolarities much lower than seawater -animals must also eliminate other metabolic waste products aside from water and salt solutions such as fats, carbohydrates, CO2, and nucleic acids containing nitrogen -most common nitrogenous waste is ammonia NH3 because it is highly toxic, ammonia must either be excreted continuiously to prevent accumulation or it must be detoxified by conversion into other molecules. Ammonia- - Highly soluble in water and diffuses rapidly - Ammonotelic- animals that excrete ammonia - Due to high accumulation of ammonia, which is harmful towards animals, ammonia must be either converted into urea or uric acid. - Humans can excrete ammonia to maintain pH level in body, can also excrete uric acid and urea Urea- - Ureotelic-animals such as mammals (e.g. humans), amphibians and cartilaginous fishes excrete urea as their principle waste product. - Quite soluble in water
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