4. The purpose of having a light source on a microscope is to allow better viewing.
I'm not sure what the full question is but it sounds like a cactus.
Answer:
Given that an amoeba is a protist (single-celled eukaryote), you should be looking at the nucleus.
Earth's atmosphere is composed of air. Air is a mixture of gases, 78% nitrogen and 21% oxygen with traces of water vapor, carbon dioxide, argon, and various other components.