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Chapter 5

Chapter 5 Online Textbook BIO120 2013.docx
Chapter 5 Online Textbook BIO120 2013.docx

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University of Toronto St. George
James Thomson

Chapter 5 9/21/2013 7:19:00 PM Chapter Concepts • Water has many properties favorable to life • Many inorganic nutrients are dissolved in water • Plants obtain water and nutrients from the soil by the osmotic potential of their root cells • Forces generated by transpiration help to move water from roots to leaves • Salt balance and water balance go hand in hand • Animals must excrete excess nitrogen without losing too much water  life relies on abiotic properties (physical/chemical properties) o things that are not living  main distinction between living and abiotic systems  organisms have a purposeful existence 5.1 Water has many properties favorable to life  Water stays liquid over a broad range of temperatures because it resists changes in temperature  Water also resists changing states o This property helps water stay liquid in winter  Water conducts heat rapidly  Water becomes less dense as it becomes cooler  water is dense (800 times denser than air), it provides support for organisms  also viscous, and resists flow or movement of a body through it o aquatic animals have adapted to reduce drag in water 5.2 Salt balance and water balance go hand in hand  when water evaporates from body surface, solutes are left, leaving a greater concentration in the body  osmoregulation  process of maintaining a proper salt balance  Plants regulation: o transpire hundreds of grams of water for every gram of dry matter they accumulate in tissue growth o uptake salt through roots o when high salt concentrations in soil, plants pump excess salts back into the soil by active transport across their root surfaces (plant’s kidneys) o leaves secrete salt by active transport  Terrestrial Animals: o Less vulnerable to water loss than plants (internal gas exchange surfaces) o Eliminate salts through urine o Desert animals have very efficient kidneys to conserve water  Ex. human kidneys can concentrate most solutes in their urine to about 4 times the levels in their blood plasma, the kangaroo rat’s kidneys produce urine with solute concentrations as high as 14 times the levels in its blood o Many animals that are not near fresh water have specialized salt secreting organs  Ex. Modified tear glands  Fresh Water Animals: o Solute concentrations depend on concentrations in environment (in the water) o The tissues in freshwater fish have higher concentrations of salt that their surroundings o HYPEROSMOTIC (higher concentrations of salt than their surroundings)  Marine animals: o HYPO-OSMOTIC (lower salt concentrations than their surroundings) o Lose lots of seawater, so must drink seawater to replace it o Sharks and rays have urea (a common nitrogenous by- product of protein metabolism in vertebrates) rather than excreting through urine  Raises osmotic potential without increase concentrations of Na + Cl ions  Downside Is that urea impairs protein function  accumulate high concentrations of a compound called trimethylamine oxide to protect proteins from its negative effects 5.3 Animals must excrete excess nitrogen without losing too
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