Question

The composition of stele is
(A) Pith, vascular bundles
(B) Endodermis, pericycle, pith
(C) Endodermis, pericycle
(D) Pericycle, pith

Answer 1

Hint: The term stele represents the pith, pericycle and vascular bundle and it’s a characteristic feature of dicot root. Secondary growth in dicot root takes place in reference to stele, which is intrastelar and extrastellar growth.

Complete answer:
The outermost layer of dicot root is epidermis. Next to that, several thin layered parenchymatous cells are present which is known as cortex. Inside the cortex, a single layer of barrel shaped cells is found without intercellular spaces. This layer is known as the endodermis, the innermost layer of the cortex.
Next to endodermis, a few layers of thick walled parenchymatous cells are found, which is known as pericycle. The pith is small or absent or inconspicuous in dicot root. Inner side of the pericycle consists of a vascular strand which has 2 – 6 alternate and radial bundles of xylem and phloem. Xylem is exarch in nature. Phloem occurs as oval patches below the pericycle in between the xylem strands.
Tissues which are present inner to endodermis, namely pericycle, vascular bundle and pith constitute the stele. Pericycle is considered as the outermost layer of stele.
Understanding the options one by one,
(A) Pith, vascular bundles
This represents stele part of the dicot root.
(B) Endodermis, pericycle, pith
This doesn’t represent stele, as it contains endodermis tissue. Endodermis is the innermost layer of the cortex and not a part of stele.
(C) Endodermis, pericycle
This also doesn’t represent stele, as it possesses endodermis tissue
(D) Pericycle, pith
This doesn’t include vascular bundles and hence not the composition of stele.

Hence the correct answer is option(A)

Note: Stele exactly represents the vascular cylinder of dicot root, which includes pith (if present), vascular bundles and pericycle (outermost layer of stele). Remember, the endodermis layer is not a constituent of stele, and it’s a part of the cortex.