There are two main ways in which molecules are transported into and out of cells - active transport and passive transport. Which of the following statements is true of passive transport?
A.
Molecules move up a concentration gradient during passive transport.
B.
Endocytosis and exocytosis are two forms of passive transport.
C.
Carrier proteins are sometimes used during passive transport.
D.
Energy, in the form of ATP, is essential for passive transport.