Wolfram, core of it is used by plant life (5)
I believe the answer is:
flora
'plant life' is the definition.
(I've seen this before)
'wolfram core of it is used' is the wordplay.
'core of' indicates the central letters (I've seen 'core' mean this).
'it is used' indicates anagramming the letters.
The central letters of 'wolfram' are 'olfra'.
'olfra' is an anagram of 'FLORA'.
'by' acts as a link.
(Other definitions for flora that I've seen before include "__ MacDonald, heroine of the 1745 Jacobite rising" , "Various plants" , "growing flowers" , "collection of plants" , "Lots of plants" .)