BY124 Mock Exam 4 answers - Mock Exam#4 1 A salt water sea...

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Mock Exam #4 1. A salt water sea star was mistakenly placed in freshwater and it died. What is the most likely explanation for its death? a. The sea star was stressed and needed more time to adapt to new conditions. b. The sea star is hypertonic to the freshwater, and it could not osmoregulate. c. The osmoregulatory system of the sea star could not handle the change in ions present in freshwater d. The contractile vacuoles used to regulate water content ruptured in the freshwater. e. The cells of the sea star dehydrated and lost the ability to metabolize energy Sea star is used to living in it natural saltwater environment so its insides have a high solute content to osmoregulate. Place it in a freshwater solution and its inside is hypertonic (higher solute concentration) to the freshwater. The sea star takes on lots of water from osmosis and dies. 2. Most of our nitrogen-containing waste products are a result of _____. a. drug use b. consumption of foods high in nitrates, such as green vegetables c. protein metabolism d. the body's attempts to maintain pH homeostasis e. metabolism of fatty foods Some of the most toxic by-products of metabolism are nitrogen-containing wastes from the breakdown of protein and nucleic acids. Forms of nitrogenous waste - Ammonia excretion most common in aquatic animals because of all the water needed - Urea – Ammonia is too toxic so it is combined with carbon dioxide to lower ammonia toxicity. Also reduces water loss. Main disadvantage is energy cost. - Uric acid – insects, reptiles and birds excrete it as a semisolid paste that doesn’t dissolve in water. Little water loss. But even more energetically expensive than Urea.
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