What common feature do all living organisms have when viewed through the microscope?

Cell membranes contain membrane proteins that allows all the interaction that occurs within the cell. It makes the cell membrane selectively permeable because of its characteristics as being fluid or its fluidity which means to say that they can move freely within the lipid bilayer. The membrane proteins can also be stored in the lipid bilayer together with the enzymes. It cannot be denied that membrane proteins have a lot of functions based on its type. They can be integral proteins, peripheral proteins and lipid bound proteins.

Well,

Another common feature all living organisms share when viewed under a microscope is DNA.  Since it is one of the criteria for life, all organisms must have it.