It is important to protect a(n) from dust

Light microscope.

Explanation:

An optical microscope is a also called as a light microscope its a type of microscope that is commonly used in visible light and has a system of several lenses that magnifies the images of the small objects. Made for the discovery of the small cells, and was made on the 17th century.

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.