Site not without oxygen, a biological supplier of nutrients (8)
I believe the answer is:
placenta
'biological supplier of nutrients' is the definition.
I can't judge whether this definition defines the answer.
'site not without oxygen a' is the wordplay.
'site' becomes 'place' (synonyms).
'without' is a deletion indicator.
'oxygen' becomes 'O' (atomic symbol for oxygen).
'not' with 'o' removed is 'nt'.
'place'+'nt'+'a'='PLACENTA'
Can you help me to learn more?
(Other definitions for placenta that I've seen before include "Source of nourishment for embryo" , "21 that feeds the embryo" , "Plate can appear in organ in womb during pregnancy" , "temporary organ" , "baby food" .)