Study GuideBiology–Excretion and Homeostasis1. Excretory SystemsAll animals producewaste productsas a result of normal life processes like digestion andrespiration. The job of theexcretory systemis to remove these wastes from the body. This processis essential for keeping the internal environment stable—a condition known ashomeostasis.What Is Homeostasis?Homeostasismeans “staying the same.”It refers to the ability of an organism to maintain astable internal balance, even when the externalenvironment changes. By removing excess water, salts, and metabolic wastes, the excretory systemplays a major role in maintaining this balance.1.1 Excretion in Simple OrganismsSingle-Celled OrganismsOne-celled organisms live in direct contact with their environment. Because wastes can easily diffuseout of the cell, theydo not need special excretory organs.1.2 Excretory Systems in Multicellular AnimalsAs organisms become larger and morecomplex, waste products must be transported away from cellsand removed efficiently. Different animal groups have evolved different excretory structures to solvethis problem.1.3 Flatworms: Flame CellsFlatworms, such asplanaria, have simple excretory structures calledflame cells.•Flame cells containciliathat beat constantly.Preview Mode
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