An organist
A person who gives an organ to another is a donor, and a person who receives an organ is a donee.
The liver
A vestigial is an organ that serves no useful function in an organism.
An informed person is a smart person.
Tissue, organ or system. Depends on what you mean by "a collection" of cells.
An organist. Same title applies to those who play digitals, too.
An organist
Organist
An Organist.
A barrel organist is a person who plays a barrel organ.
A "harmonicanist" is what a person who plays the harmonica is called.
A person who plays Scrabble is called a Scrabbler. (unofficially)
A drummer or percussionist plays the drums.
harpist
a cymbalist
Guitarist
a baritonist