BIO

BIO Chapter 21: Gas Exchange and Excretory Systems Section: Gas Exchange in Multicellular Organisms Question: Where are the structures involved in gas exchange located' Answer: Organs for gas exchange have evolved differently in various organisms, yet they all have a common function: exchanging gas molecules between cells and the external environment Support: 21.1 Variation in Gas Exchange Systems Organs for gas exchange have evolved differently in various organisms, yet they all have a common function: exchanging gas molecules between cells and the external environment Small multicellular animals, such as planarians, obtain oxygen and give off carbon dioxide directly through their body surfaces The respiratory organs found in many animals that live in water are called gills Gills provide these water dwellers with a large respiratory surface Water contains dissolved oxygen, but only in small amounts To satisfy the need for oxygen in a fish, for example, water must constantly pass over the gill surfaces Gills are highly efficient gas exchange organs The filaments of gills are made up of thin disklike structures lined up parallel with the direction of water movement 21.2 Gas Exchange in Terrestrial Organisms When organisms moved onto land, air became the source of their ocygen Water is relatively poor in oxygen It contains only about 5 to 10 mL water, organisms, through, oxygen, blood, body, exchange, called, air, dioxide, carbon, system, reabsorption, gas, urinary, tubule, organs, nephron, materials, wastes, salt, out, nitrogenous, must, lungs, kidneys, gills, excretion, balance, waste, transport, secretion, removed, plasma, ions