Carbon Cycle Chemical Reactions Involved: Photosynthesis: Air and water molecules and the energy from the sun to produce a simple sugar such as glucose and oxygen molecules as a by product. During photosynthesis plants use carbon dioxide and produce oxygen.
Similar to shore power for ships, a ground power unit (GPU) may be used to supply electric power for an aircraft on the ground, to sustain interior lighting, ventilation and other requirements before starting of the main engines or the aircraft auxiliary power unit (APU).
In the diagram above, the computer supplies current to the relay, which is grounded. Once energized, the relay conducts power to the fuel pump. This arrangement allows the computer to control the pump which is too heavy to control directly. A typical automotive relay has four or five terminals.