Here's a breakdown:
* -ist: A suffix that signifies a person who is involved in or associated with something.
* Biologist: Someone who studies living organisms.
* Chemist: Someone who studies chemistry.
Other examples:
* Artist: Someone who creates art.
* Pianist: Someone who plays the piano.
* Activist: Someone who advocates for a cause.
* Socialist: Someone who believes in socialist principles.
* Atheist: Someone who does not believe in God.
In essence, "-ist" marks a person who is a specialist or practitioner within a specific area.