The two major divisions of the human nervous system are the central nerves and the peripheral nerves.
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biology and chemistry/physics and chemistry
Tissue. Level, organ and. Organ sytem level
To identify every human gene.<==== nova net answer.
I'd suggest the two major divisions would be that separating the life sciences (botany, biology, anthropology ..) from the 'exact sciences' (physics, chemistry, astronomy, nuclear physics ..).
The skeletal system is a major repository of calcium.