We think that the are the same size and shape of bacteria because they used to be bacterial cells on their own that became part of our cells

what statement best describes the difference between the sympathetic and parasympathetic nervous systems?

the sympathetic nervous system prepares the body for intense physical activity and is often referred to as the fight-or-flight response. the parasympathetic nervous system has almost the exact opposite effect and relaxes the body and inhibits or slows many high energy functions.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.