The digestive system. The digestive system breaks down food to provide the body with energy.
During an avalanche the potential energy of the snow on the mountain is converted into kinetic as the snow rushes downward.
Bacteria can be beneficial. The example of how bacteria are beneficial is that they A. break down cellulose in some animals' digestive systems.
The tricuspid valve shuts. This prevents blood from flowing backward into the right atrium while the ventricle contracts. So, your answer will be the Tricuslid Valve. Hope I helped!