In what ways does carbon enter the hydrosphere?

When oxygen is present, aerobic respiration occurs, which releases carbon dioxide into the surrounding air or water. Otherwise, anaerobic respiration occurs and releases methane into the surrounding environment, which eventually makes its way into the atmosphere or hydrosphere.

i think it would be b. tissue because an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.