There are microbes everywhere humans go, including the Space Station. The crew must keep them under control. Clean Air for the Space Station - Life support systems on the Station must supply oxygen and remove contaminants in the Station's air. The Station must provide clean water for the crew. Any time we drop or throw something and watch it fall to the ground we see gravity in action.
Gravity is a universal force, but sometimes scientists want to do research without gravity's pull.
Microgravity can be created by dropping an object. In everyday life we feel our weight because the surface of the Earth holds us and keeps us from falling to the Earth's center. In free fall, there is no force holding the object back, so as it falls, it doesn't experience the sensation of weight. Microgravity can be made briefly on Earth by dropping objects from tall structures, and can be created for longer periods in airplanes, rockets and spacecraft.