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Lecture 33

BIOL 2200 Lecture 33: Lecture Notes Excretion

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University of Virginia
BIOL 2200
Jessamyn Manson

4/17/17 Lecture 33 Notes Excretion  Nitrogenous Waste o Waste product from using protein and nucleic acids and breaking them down o Can be toxic (ammonia), so must be removed o May take different forms to remove toxicity  3 Types of Nitrogenous Waste: o Ammonia (hydrogen added to NH2)  Made with low energetic cost  Toxic and must be diluted to be excreted from body safely  Found in aquatic animals (most bony fish) o Urea  Combines ammonia with CO2 in liver  Low toxicity  Energetically costly (combining ammonia with CO2)  Produced in many land animals o Uric Acid  Relatively non-toxic  Doesn’t dissolve in water, reducing excretory water loss  VERY energetically costly  Reptiles, birds, insects o General trend: the more complex the molecule, the less toxic but more energy required  What determines nitrogenous waste? o Type of nitrogenous waste based on:  Environment (aquatic animals produce ammonia, land animals produce urea and uric acid)  Evolutionary history  Immediate environment of egg: shell-less vs. amniotic egg o Amount of nitrogenous waste  Clicker: Which animals most likely makes the most nitrogenous waste?  a. Insectivorous frog  b. Frugivorous bat  c. Piscivorous seal  d. Granivorous bird o Why? Seals are endotherms (energetically costly) and eats protein, producing lots of waste  4 Steps to Excretion o o Filtration  Body fluid contacts membrane of an excretory tubule  Water, small solutes cross membrane to form filtrate o Reabsorption  Water and essential solutes (sugars, important ions) leaves the filtrate and goes back into blood  Some are passively transported and some actively transported o Secretion  Some solutes move back into blood by diffusion  Toxins are moved from blood into filtrate to be excreted o Excretion  Filtrate released as urine  Mammalian Excretory System o o o Kidneys are paired organs o Excretory tubules (nephrons)
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