Said they'd purchase mushrooms to demonstrate part of anatomy (6)
I believe the answer is:
biceps
'part of anatomy' is the definition.
'biceps' can be an answer for 'part' (biceps is a kind of part). I'm not certain of the 'of anatomy' bit.
'said they'd purchase mushrooms to demonstrate' is the wordplay.
I cannot quite understand how this works, but
'mushrooms' could be 'ceps' (cep is a type of mushroom) and 'ceps' is located in the answer.
The remaining letters 'bi' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for biceps that I've seen before include "Arm workers" , "Weightlifters use them" , "Type of muscle" , "Contractor" , "Upper-arm muscle" .)