Answer:There are a series of __parts_____________ in the body that regulates all of the __activites_____________ that are necessary to sustain life. A system is a combination of many smaller __organelles_____________ 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 _systems______________ instead of organs to accomplish all of the activities that are necessary to sustain life.