Answer: There are a series of systems in the body that regulates all of the activities that are necessary to sustain life. A system is a combination of many smaller parts that makes up a whole. A system has both a input and an output. There are at least nine body systems in the human body. Many other organisms in the world also have these body systems. Unicellular organisms that lack the complex organization of multicellular organisms use their organelles instead of organs to accomplish all of the activities that are necessary to sustain life.
Or 1. systems 2. activities 3. parts 4. input 5. nine 6. body 7. organelles
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