Which statement best explains how organ systems in the human body function A. They work at different times to conserve energy
B. They work together to benefit the entire organism
C. They work at different times, depending on their job
D. They work independently of each other, for efficiency

Ivan is looking at a cross section of a stem taken from a vascular plant. he sees two different types of vascular tissue: the xylem, which is closer to the center of the stem, and the phloem, located around the xylem, closer to the outside of the stem. how do these two structures work together in a living plant?