Homeostasis and Excretion Chapter 44 Presentation by: Imani Phillips, Stephanie Riley, and Jamie Chavez

Osmoregulation and Excretion Osmoregulation: how animals regulate solute concentrations and balance the gain and loss of water Excretion: how animals get rid of the nitrogen-containing waste products of metabolism

Osmosis Osmolarity: total solute concentration expressed as molarity or moles of solute per liter of solution –Unit of measurement: milliosmoles per liter(mosm/L) where 1 mosm/L = a total solute concentration of M –Osmolarity of human blood= 300 mosm/L while osmolarity of seawater= 1000 mosm/L When tow solutions differ in osmolarity, –The one with greater concentration of solutes is hyperosmotic –The more dilute solution is hypoosmotic When two solutions separated by a selectively permeable membrane have the same osmolarity they are said to be isoosmotic

2 Basic Solutions to the Problem of Balancing Water Gain with Water Loss Osmoconformers: –Available only to marine animals that mostly live in water that has a very stable composition –Does not actively adjust its internal osmolarity Osmoregulators: –An animal that must control its internal osmolarity because its body fluids are not isoosmotic with the outside environment

Energy Cost of Osmoregulation Osmoregulators must expend energy to maintain the osmotic gradients that cause water to move in or out Energy Cost depends on –how different an animal’s osmolarity is from its environment –how easily water and solutes move across the animal’s surface –how much work is required to pump solutes across the membrane Adaptations also help to reduce the energy cost by reducing the amount of water lost –ex: many animals that live in the desert are nocturnal. This reduces water loss by taking advantage of lower temperature and higher relative humidity of night air.

Transport Epithelia Is a layer or layers of specialized epithelial cells that regulate solute movements Moves specific solutes in controlled amounts in specific directions

Nitrogenous Wastes When proteins and nucleic acids are broken apart for energy or converted to carbohydrates or fats, enzymes remove nitrogen in the form of ammonia which is very toxic The amount of nitrogenous waste produced is tied to the energy budget because it strongly depends on how much and what kind of food the animal eats Endo- therms VS. Ecto- therms Preda- tores VS. Herbi- vores Produce energy at high rates Eats less than most endo- therms Gains energy from dietary proteins Relies on lipids & carbohydr ates as energy sources So Endotherms>Ectotherms in producing nitrogenous wastes So Predators>Herbivores in producing nitrogenous wastes

Forms of Nitrogenous Wastes AmmoniaUreaUric Acid Ammonia excretion is most common to aquatic species because –there needs to be lots of access to water –its toxicity only makes it possible to be excreted in large volumes of very dilute solutions In many vertebrates, ammonia release occurs across the whole body surface Excreted by most terrestrial animals and many marine species Low toxicity Can store urea at high concentrations Urea-excreting animal requires much less water Animals must expend energy to produce it from ammonia Excreted by insects, land snails, and many reptiles Relatively nontoxic Largely insoluble in water Can be excreted as semi-solid paste with very little water loss Even more energetically expensive to produce than urea Needs ATP for synthesis from ammonia