You may be surprised if it goes up (7)
I believe the answer is:
eyebrow
'it goes up' is the definition.
The definition suggests a singular noun which matches the answer.
'you may be surprised' is the wordplay.
I cannot really see how this works, but
'you' could be 'ye' (historical version of 'you') and 'ye' is found in the answer.
This explanation may well be incorrect...
'if' acts as a link.
Can you help me to learn more?
(Other definitions for eyebrow that I've seen before include "feature one might raise?" , "one's raised disapprovingly" , "Facial hair (that can be raised)" , "It may be raised" , "surprisingly elevated" .)