Organ system is the answer
If a researcher electrically stimulates the reticular formation in an animal, the animal will immediately wake up and be alert. Its purpose is to have some control of sensory signals and thus has the ability to alert the body when it is tired or needs to be awake.
The digital signal can then be recorded, edited, and modifies using digital audio tools. A transducer which converts sound pressure waves into electrical signals. a digital-to-analog converter will convert a digital signal back into an analog signal, which analog circuits amplify and send to a loudspeaker.
A. It’s the thing you change and you’ll measure the E. coli growth