Regulation of iron absorption and transport. Iron for use in synthesis of heme, iron-sulfur centers and other non-heme iron proteins is obtained from the diet and via release of recycled iron from macrophages of the reticuloendothelial system that ingest old and damaged erythrocytes (red blood cells).
Four-stroke oil is more like the oil used in cars but both 2-stroke and 4-stroke oil serve the same purpose - to keep the engine lubricated. Four-stroke dirt bike oil comes in a variety of weights like 10w-40, 20w-50 and so on. It is not mixed with gas.
GNCC Enduro bikes are all 450cc but typically have different suspension and larger gas tanks, among other differences from dirt bikes equipped for Supercross or Motocross. Riders eventually lap around back to the pits and can fill up, get new tires or address any mechanical issues if needed.