Cases of word usage

1) a very small organism (in the air, food etc) that can cause disease (germ)

2) (an instance of) a change in the basic structure of a living or developing organism which can affect the shape, size etc (mutation)

3) any living organism that is not an animal, especially the kind smaller that trees and shrubs; a large factory; to put plants, bushes, trees etc in (a garden etc) (plant)