Question

In the T.S. of root shows
A. Protoxylem and metaxylem are not present on same radius
B. Metaxylem is towards inside and protoxylem towards outside
C. Protoxylem towards inside and metaxylem towards outside
D. Both A and B

Answer 1

Hint: The various cells and tissues of primary root arise from apical meristems which are situated at sub terminal position. The root generally shows simple internal structure as compared to stem as it has no buds, nodes, internodes and lateral appendages.

Complete answer:
Depending upon the time of origin in relation to development and structural differences, the xylem is of two types- protoxylem and metaxylem.
The protoxylem is the first formed xylem in which the lignification starts before the completion of the elongation. It is usually made up of tracheids, vessels, and xylem parenchyma.
The late formed xylem is called metaxylem and it bears larger tracheids and vessels. In this case, lignification takes place after the completion of elongation.
Depending upon the relative positions of protoxylem and metaxylem, xylem is of three types:
> Exarch- In this type, the protoxylem lies towards the outside of the metaxylem, for example in roots.
> Endarch- n this condition, protoxylem lies towards the centre of the axis, for example, in stems.
> Mesarch- In this, protoxylem lies in the middle of metaxylem, for example in ferns.
The arrangement of xylem and phloem strands is the characteristic of a particular organ. The different types of arrangements of vascular bundles are:
> Radial- In this the xylem and phloem strands alternate with each other separated by parenchymatous cells. It is found mainly on roots.
> Conjoint- It is the type of vascular bundle having both xylem and phloem together. Normally these occur in the same radius and they occur in stems.

Both A and B are correct answers for this.

Note: The conducting region of a plant is formed of xylem and phloem. These form complex permanent tissues. Xylem is responsible for conduction of water and dissolved minerals while phloem conducts food.