AP BIOLOGY

Detailed explanation-1: -Older xylem (heartwood) can be recognized because of its darker color, and it is found towards the center of the stem (Figure 5). This older xylem is no longer functional, however both sapwood and heartwood provide mechanical support for the plant.

Detailed explanation-2: -No, there are no living cells in the heartwood. Heartwood is the compressed and dead xylem tissue of a tree.

Detailed explanation-3: -The heartwood, the inner zone of the xylem, is physiologically inactive regarding water conduction. With tree ageing, the parenchyma cells die, lose their reserve material and the wood becomes impregnated with com-plex organic compounds.

Detailed explanation-4: -E: Heartwood is the central, supporting pillar of the tree. Although dead, it will not decay or lose strength while the outer layers are intact. A composite of hollow, needlelike cellulose fibers bound together by a chemical glue called lignin, it is in many ways as strong as steel.