Student or Learner
In my opinion, microscopes are used to look at tiny objects that you cannot see in the naked eye.It is used to examine blood cells, bacteria, cell cultures, immuno-staining,micro injections and other organisms. It is used to discover diseases and precancerous cells.It is also used for looking at pap smears, and other specimens of any body site.
This is your opinion?
Watch your use of singular and plurals. You refer to microscopes, then you use "it."
You cannot see WITH the naked eye.
You may discover the presence of a disease, but not a disease. (Ray may have more commentary on this part.)
I don't believe staining and injections can be considered organisms.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.