Chapter 44

2. Osmolarity is the total concentration of a solute expressed in mols. An isoosmotic solution is separated by a selectively permeable membrane in which concentrations are equal. An hyperosmotic solution is a solution whose solute concentration is greater than that of a solution separated by a permeable membrane, and a hypoosmotic solution is one whose solute concentration is less than that of a solution separated by a permeable membrane.
4. A stenohaline is an animal that is unable to tolerate substantial changes in external osmolarity, while an euryhaline is an animal that is able to tolerate substantial changes in external osmoregularity.
6. Saltwater fish that are hypoosmotic to their surroundings ingest large amounts of sea water and produce high concentrations of urine and excrete salt ions from the gills, while a freshwater fish which is hyperosmotic to its surroundings takes up salt ions through food and gills and produces large amounts of dilute urine.
8. Land animals ingest liquid water, ingest moist food and produce via metabolism in order to conserve water.
10. Transport epithelium is one or more layers of specialized epithelial cells that regulate solute movement. They help to regulate excretion and osmoregulation by transporting solutes in and out of cells.
12. Ammonia is the nitrogenous waste that is excreted by most aquatic animals. It requires vast amounts of water for dilution but little ATP to produce. Urea is nitrogenous waste excreted by mammals, most amphibians, sharks, and some bony fishes. It is a less toxic method of excretion requiring less water for dilution, but requires more ATP to produce. Uric Acid is the nitrogenous waste excreted by reptiles, insects, and land snails. It is insoluble in water and can be excreted with little water loss, but it but requires great amounts of ATP to produce.
14. There are four key steps. The first is collection and filtration. Filtration is the collection of fluid through selectively permeable membranes consisting of a single layer of transport epithelium. During this process, membranes retain cells, proteins, and large molecules. It forces water, solutes, and nitrogeous wastes into excretory system. The next step is selective reabsorption, which is the reabsorption of valuble solutes from filtrate by active transport. Next is selective secretion, which is the addition of nonessential solutes and toxins by active transport. Finally, excretion occurs.
16. In a protonephridium, water and solutes from interstitial fluid are drawn into protonephridium by beating of flame bulb cilia. Then filtrate moves through tubules to nephridiopore in body wall and is excreted. The process is very similar in metanephridium, which is a network of tubules with internal openings used in excretion
18. Kidneys are the excretory organ of vertebrates. The renal artery is the artery that supplies blood to the kidneys. The renal vein drains blood from the kidneys. The ureter is the duct through which urine exits. The urinary bladder is the storage area where urine is held.