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152-Exretory worksheet_key

152-Exretory worksheet_key - Intro Bio 152 Discussion...

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Intro Bio 152 Discussion – Excretory Worksheet – Spring ‘09 1. The removal of nitrogenous wastes (excess nitrogen) is a special problem in most animals. a. Where does the nitrogenous waste come from? The primary source of nitrogenous waste is deamination of amino acids. This occurs when excess protein is consumed or when dead or damaged cells and other substances are removed from the body. b. What is it about the chemistry of nitrogen that makes it difficult for most animals to deal with? Amine groups are easily converted to ammonia (NH 3 ), which is very soluble in water (NH 3 + H 2 O NH 4 + + OH - ). It is also toxic, however. As a result, large quantities of water must be readily available to organisms that excrete ammonia. For most terrestrial animals, water availability is limited. In these animals, the ammonia produced by deamination is converted to a less toxic form, either urea or uric acid. 2. Complete parts a and b, and then use the information you gather there to answer the question in part c. a. Describe the composition of the newly filtered solution that enters Bowman’s capsule. Then compare it to the composition of the blood entering and leaving the glomerulus. The solution that enters Bowman’s capsule contains water and anything soluble in water that is found in the blood. Among other things, this solution includes salts, water-soluble medicines and drugs, sugar, vitamins, and nitrogenous wastes. The concentrations of these substances in the fluid entering Bowman’s capsule are similar to their concentrations in the blood that enters the afferent arteriole. b. Starting with the solution that is filtered into Bowman’s capsule from the glomerulus, describe the changes that occur in its composition as it moves through each of these regions: i. Proximal convoluted tubule In this region, NaCl and nutrients (for example, sugars) are actively transported out of the filtrate and into the cortex of the kidney. Bicarbonate ions, potassium ions, and water passively diffuse into the cortex. They are picked up by capillaries and returned to the blood. In this same region,
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