In what type of solution is a contractile vacuole useful? (Hypertonic/hypotonic/isotonic) Also, why wouldn't it be helpful in the other two solutions?

What sentence best supports the statement that hormones are involved in the regulation of homeostasis? a. the hormone erythropoeitin increases the production of red blood cells when oxygen levels are low. b. the hormone oxytocin promotes labor contractions of the uterus during childbirth. c. the hormone melatonin induces sleep and its production is slowed by exposure to light. d. the hormone cortisol suppresses the immune system and is produced when the body is under stress.

Select the correct answer from each drop-down menu proteins are

How many pounds does the earth weigh?