Worldwide circulation and reutilization of carbon atoms, chiefly due to metabolic processes of living organisms. Inorganic carbon, in the form of carbon dioxide, is incorporated into organic compounds by photosynthetic organisms; when the organic compounds are broken down in respiration, carbon dioxide is released. Large quantities of carbon are "stored" in the seas and the atmosphere, as well as in fossil fuel deposits.
3 is the correct answer. Let me know if you want me to explain why that is the answer.
Gates function in a similar way as cell membrane :
cell membrane seperate the external enivironment from the cell while gate even seperate the external environment from the house
cell membrane controls the exit and entry of the cell, gate controls the entry and exit of the house
