Question

Exarch and polyarch condition is found in
a. Monocot stem
b. Dicot stem
c. Monocot root
d. Dicot root

Answer 1

Hint: Vascular bundles arrangement is different in monocot and dicot stem. Radial arrangement is observed in monocot roots. Xylem and phloem have eight bundles and this condition is called polyarch. In dicot stem, xylem is on the inner surface and described as endarch. These are also described as radial and tetarch.

Complete answer:
In monocot root, secondary growth is absent, xylem and phloem are radial, and around central pith xylem and phloem are arranged in circular fashion many xylem bundles and exarch condition is found in monocots.

In dicot root, the number of xylem and phloem are equal in number that is 2 to 6. Xylem and phloem are arranged alternately, that is they lie on different radii hence called radial bundles. Number of rays is equivalent to the number of xylem or phloem bundles. Number of rays is equivalent to the number of xylem or phloem bundles. Dicot roots may be diarch, triarch, tetrarch, pentarch or hexarch on the basis of the number of xylem and phloem present in roots.

Vascular bundles of monocot stem are many in number and xylem endarch. Vascular bundles in the dicot stem are eight in numbers arranged in the form of a broken ring. Dicot stems have Conjoint, collateral and open vascular bundles. Phloem and xylem present on the outer and inner side respectively.

From the above information we can conclude that exarch and polyarch condition is found in monocot root.
Hence, the correct answer is option (C).

Note: Vascular bundles can be closed or open. If no cambium is found between xylem and phloem then it is said to be as closed vascular bundles. This type of cambium is unable to grow laterally. Dicot roots have small pith while in monocot root large pith is found. Tulips, onions, and garlic etc are some examples of monocotyledons; carrot is an example of dicot root.