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.
Kids as young as 3-years-old can start on small electric dirt bikes, and can safely ride a gas-powered 50cc dirt bike at age 4 with training wheels. At age 5 or 6, they can be zipping around without training wheels and even taking small jumps on real dirt bikes.