Question

Inner darker, harder portions of the secondary xylem that cannot conduct water in the older dicot stem is called?
A. Alburnum
B. Bast
C. Duramen
D. Wood

Answer 1

The secondary xylem is divided into two parts: The Heartwood which is situated in the central portion and the sapwood which is there is the peripheral area. The Heartwood is dark and crushed with a narrow lumen whereas the sapwood is scattered around the central and has a comparatively broader lumen.

Complete Answer:

Bast is the other name of Phloem (the permanent tissue which transports the prepared food to different parts of the plant) and hence has nothing to do with any part of secondary xylem.
The portion of the secondary xylem that is functional is called Duramen. The location of Duramen is peripheral. The other name of Duramen is Sapwood. Therefore, it is not the inner part of secondary xylem.
Wood is the common term used for the secondary xylem as a whole. It consists of both the Heartwood and Sapwood. Hence, it is not the specific name for the inner darker, harder portion of the secondary xylem.
Alburnum is the other name for Sapwood. Hence, we can say that the inner portion of the secondary xylem which is non-functional hence cannot conduct water.

Note: Alburnum and Duramen together form the wood. Hence wood is commonly used for secondary Xylem. Alburnum or Heartwood is the non-functional part of secondary xylem, the reason for the non-functionality of this portion of secondary xylem is mainly due to the pressure exerted by Sapwood upon it.