Learning Outcomes BIOL1082 -- 3/8

Describe the different kinds of nitrogenous waste, their relative toxicity and solubility, and list which animals excrete each of them.

-ammonia: produced from metabolism of amino acids and nucleic acids; an amino group (NH2) is removed and combined with an H+ to form ammonia (NH3); very toxic, only safe in dilute concentrations; bony fishes and tadpoles excrete ammonia by diffusion through gills and less by excretion in dilute urine -urea: less toxic than ammonia and water-soluble, excreted in large amounts in the urine, carried in the bloodstream from liver to kidneys where it is excreted; excreted by elasmobranchs, adult amphibians, and mammals -uric acid: insoluble/low-solubility in water, uric acid forms a precipitate and can be excreted using very little water; costs the animal energy to synthesize uric acid yet is offset by conservation of water; excreted by reptiles, birds, and insects

Compare and contrast the structure and function of the osmoregulatory organs of flatworms, earthworms, and insects, detailing where and how the process of filtration, reabsorption, secretion, and excretion occur.

-flatworms: protonephridia tubules branch throughout body into bulblike flame cells, cells open to outside of the body but not inside; movement of cilia in flame cells draw fluid from the body. water and metabolites are reabsorbed and substances to be excreted are expelled through excretory pores. -earthworms: have tubules known as nephridia that open to the inside and the outside of the body. nephridia obtain fluid from body cavity through filtration into nephrostomes. filtration: fluid is formed under pressure and passes through small opening so large molecules are excluded. reabsorption occurs through transport out of the body and into the surrounding body fluids -insects: utilize Malpighian tubes as excretory organs; these tubes are extensions of the digestive tract that branch off anterior to the hindgut; waste molecules and potassium are secreted into these tubules by active transport -reabsorption: transport out of tubule into surrounding body fluids -secretion: ions or molecules are transported from body fluid into tubule

Compare and contrast osmotic challenges faced by animals in freshwater, marine, and terrestrial environments, and the adaptations used to address them.

-freshwater vertebrates: higher solute concentration in bodily fluids than surrounding water and thus water tends to enter their bodies; have adapted to prevent constant flow and remove excess water from their bodies along with having to transport ions back into their bodies. -marine vertebrates: low solute concentration compared to environment and thus are in danger of losing water so they have adapted to prevent dehydration by drinking seawater and eliminating excess ions through kidneys and gills. -terrestrial vertebrates: higher water concentration in body than external environment, face problem of losing water by evaporation from skin and lungs and have evolved an urinary/osmoregulatory system to help them retain water.

Distinguish among the approaches used by osmoconformers and osmoregulators, listing examples of each.

-osmoconformers: in osmotic equilibrium with their environment; osmoconformers' body fluids osmolarity is the same as sea water environment; because extracellular fluids are isotonic to seawater so no osmotic gradient exists, thus no water leaves or enters the body. ex. hagfish are strict osmoconformers: keep body fluids isometric with seawater by using the same ions found in the seawater. -osmoregulators: animals that maintain relatively constant blood osmolarity despite different concentration in surrounding environment. must closely regulate body osmolarity, do so by regulating salt concentration within the body. ex. freshwater fish;