Demanding part of process consumes energy (5)
I believe the answer is:
steep
'demanding part' is the definition.
'steep' can be an answer for 'demanding' (thesaurus). I'm unsure of the 'part' bit.
'process consumes energy' is the wordplay.
'process' becomes 'step'.
'consumes' means one lot of letters goes inside another.
'energy' becomes 'e' (physics symbol as in E=mc2).
'step' enclosing 'e' is 'STEEP'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for steep that I've seen before include "Quickly rising" , "Having a sharp incline" , "Rapidly rising" , "Rising sharply" , "Difficult" .)