Get me a replacement cell (6)
I believe the answer is:
gamete
'cell' is the definition.
(gamete is a kind of cell)
'get me a replacement' is the wordplay.
'replacement' is an anagram indicator.
'get'+'me'+'a'='getmea'
'getmea' anagrammed gives 'GAMETE'.
(Other definitions for gamete that I've seen before include "something seedy?" , "Male or female germ cell" , "Germ cell in reproduction" , "Egg- or sperm-cell" , "Reproductive cell" .)