It is the main message or idea the author is trying to convey to the reader. The theme is the author's opinion of the subject.
Usually, I only take notes on key points and definitions.
When studying for a test, I give myself two notecards, and I reread everything throughout the section. The notecards are small enough that they force you to only take notes on the most important sections, and often times, those are the things that come in tests :)
Answer:
which is not a function of a vacoule
digest molecules
