The verb "to agitate" means to move, to disturb or to excite something. It can be used literally: "The hurricane winds agitated the sea." Or you can use it to mean that someone is emotionally excited, often with a negative connotation. "The more she spoke of the incident, the more agitated he got." It excited/moved him, but in the sense that he does not like what she is talking about, so this makes him feel uneasy. "Alchemy" is something they did in the Middle Ages. They wanted to find a way to create gold from other metals. This word is now also used to mean magic. "The effect was easy to dismiss as alchemy, but there had to be a good explanation." "Algae" is sort of a scientific term, so I found a good explanation of it in the dictionary: "unicellular or multicellular organisms formerly classified as plants, occurring in fresh or salt water or moist ground, that have chlorophyll and other pigments but lack true stems, roots, and leaves. Algae, which are now regarded as protoctists, include the seaweeds, diatoms, and spirogyra" If you'd like to use it in a sentence... "The pool was not cleaned in such a long time that algae had formed on its surface."