What is a description of something that includes a number and a unit

The number of living organisms in a particular area is

Body temperature is tightly regulated in mammals for example when external temperatures drop too much the body of a mammal responds by in order to its core temperature?

Which statement describes a way in which the digestive and excretory systems work together? a. the nephrons absorb nutrients from food going to the large intestine. b. the excretory system balances blood gases in the small intestine. c. the intestinal villi filter blood and send wastes to the bladder. d. the excretory system balances the salts and water obtained from digested food