Cells initially needing permission to divide? (6)
I believe the answer is:
cleave
'divide?' is the definition.
(I know that cleave is a more specific form of the action tear)
'cells initially needing permission' is the wordplay.
'initially' says to take the initial letters.
'needing' says to put letters next to each other.
'permission' becomes 'leave' (leave is permission or authorisation).
The first letter of 'cells' is 'c'.
'c'+'leave'='CLEAVE'
'to' is the link.
(Other definitions for cleave that I've seen before include "To separate and to adhere" , "remain attached" , "Separate with violence" , "Part" , "Adhere or split apart" .)