Have you had the chance to watch a tree grow over a span of several years? Did you notice that the tree grew thicker and taller? Deep in the roots of the tree and high in the growing shoots are meristem cells. Each year, the meristem cells help the tree continue to grow. As a tree ages, it needs to keep making more xylem and phloem cells to carry water and food.
Which statement explains how this occurs?
A. Xylem and phloem from one part of the plant are transferred to another part.
B. The existing xylem and phloem divide to make more xylem and phloem.
C. Cell division is not necessary for a plant to create new xylem and phloem cells.
D. Meristem cells divide and some of the new cells differentiate into xylem and phloem.