The material covered on pages 704-710 will not be covered in lecture but will be tested upon. All of Chapter 51 should be read. Terrestrial organisms particularly need to be able to eliminate the waste products of nitrogen metabolism that can be toxic. Reabsorption is the conserving or reclaiming of something that has been filtered into the potential urine by moving it back into the blood.
Marine invertebrates can be osmoconformers because they live in salt water.
Some organisms are osmoregulators and use various anatomical and physiological mechanisms to regulate the salt and water concentrations in their body tissues. To osmoregulate in fresh water, organisms need to excrete water and conserve solutes so they generally produce large amounts of dilute urine. To osmoregulate in salt water, organisms need to excrete solutes and conserve water so they generally produce small amounts of concentrated urine. The breakdown products from the metabolism of carbohydrates and fats are simply water and carbon dioxide that are easy for an organism to excrete. Organisms that cannot get rid of ammonia safely and easily convert the ammonia to the less toxic urea or uric acid for excretion.