Final answer:
To observe living organisms less than 1 millimeter in size in a water sample, John should use a compound light microscope. It allows the observation of living microorganisms under magnification without killing them, unlike staining techniques or electron microscopy.
Step-by-step explanation:
John needs to observe organisms that are less than 1 millimeter in size from a water sample collected from a stream. The best microscope to use for viewing living organisms of this size is a compound light microscope. This type of microscope uses visible light that passes through a system of lenses to magnify small specimens, making it ideal for studying living microorganisms in water. Electron microscopes, such as scanning electron and transmission electron microscopes, are not suitable for viewing living specimens because the preparation process and the vacuum environment required for electron microscopy would kill the organisms. Furthermore, dissecting light microscopes are better suited for larger specimens that do not require high magnification.
When viewing specimens through a light microscope, scientists often use special stains to make it easier to see the individual components of cells. However, it is important to note that staining usually kills the cells, which would not be appropriate for John's goal of observing living organisms.