Function: Exchange with Environment
<p id="N110B7">Every cell needs to take in nutrients and get rid of waste products. This is accomplished via processes that exchange molecules across the cell membrane. For a single-celled organism, this is accomplished through direct exchange with the environment. It gets more complicated with larger organisms where cells are not in direct contact with the “outside” environment. In such organisms, including humans, there are specialized organ systems that serve as interfaces with the environment, moving things into, and out of, the body to keep it functioning. The two major organ systems that serve to exchange nutrients and waste with the environment are the digestive system (food and feces) and respiratory system (oxygen and carbon dioxide).</p>
<p id="N110BA">Humans take in food, water and oxygen. During digestion and metabolism, food is broken down into simpler substances (including some waste products), and some of those simpler substances—for example, simple sugars—can be metabolized in a way that they release energy, especially when oxygen is present. The products of these processes include solid waste, liquid waste, and carbon dioxide. These waste materials must be eliminated from the body to prevent illness. The urinary system also helps with removal of wastes being transported in the body fluids, but the “exchange” is all internal so it will be explored more in next the vital function category.</p>
<p><a href="https://oli.cmu.edu/jcourse/workbook/activity/page?context=df3c7a9d0a0001dc2e2cd6a6ed8f3855">Source</a></p>