Head torn about information that's necessary for survival (8)
I believe the answer is:
nutrient
'that's necessary for survival' is the definition.
(nutrients are necessary in a diet)
'head torn about information' is the wordplay.
'head' becomes 'nut' (informal term for somebody's head).
'torn' becomes 'rent' (synonyms).
'about' indicates putting letters inside.
'information' becomes 'i' (common abbreviation for information).
'rent' placed around 'i' is 'rient'.
'nut'+'rient'='NUTRIENT'
(Other definitions for nutrient that I've seen before include "Source of nourishment" , "Substance to give energy and build tissue" , "Substance that provides nourishment, may be included in 6 Down" , "Feeding" , "It gives energy and builds tissue" .)