Question

Heartwood is
A. Outer part of secondary xylem
B. Inner part of secondary xylem
C. Outer part of secondary phloem
D. Inner part of secondary phloem

Answer 1

The heartwood or the duramen is the central wood of the trees. It is dark in color due to the presence of tannins or other substances. It is also aromatic. It is very strong and resistant to decay types of wood. It is formed by the secondary growth of the water-conducting vascular tissue.

Complete answer: The heartwood refers to the secondary growth of the xylem tissue. It is water-conducting tissue that lies inside the cambium layer during secondary growth. The secondary growth of the xylem results in the formation of secondary xylem that lies inside the vascular cambium. This forms the heartwood or the duramen. Heartwood is resistant to decay and less easily penetrated by wood preservatives. It is aromatic and dark in color due to the tannin's composition. The living and the functional layers of sapwood converts to heartwood in secondary growth.
The heartwood is non-functional wood as it forms from the functional sapwood cells that lie outward to it. The sapwood makes the newer growth rings and is derived from the outer part of the secondary xylem. The dead cells make heartwood very stronger and durable. For these characteristics, it is used in flooring, making of tool handles, and even for marine bridges.
Hence, the right answer is option B. Inner part of secondary xylem

Note: The woods just like their mother tissue are composed of tracheids, vessel members, parenchyma, and fibers. But the hardwood cells are dead and cannot perform transportation and storage of materials. Also, they cannot respire. Thus, the layer under the wood tissue called the periderm consists of lenticels that help the bark of the woody trees to respire.