Jack in tundra is exposed (5)
I believe the answer is:
raise
'jack' is the definition.
(I've seen this before)
'in tundra is exposed' is the wordplay.
'in' indicates the answer is hidden within the clue.
'RAISE' can be found hidden inside 'tundra is exposed'.
(Other definitions for raise that I've seen before include "Exalt" , "better?" , "Advance" , "Lift up, bring up" , "climb" .)