Question

Secondary meristem produces
A. Basal growth
B. Radial growth
C. Transverse growth
D. Vertical growth

Answer 1

Meristems are clusters of cells that allow the essential body pattern established during embryogenesis to be reiterated and extended after germination. They divide to grant rise to at least one cell that continues to be meristematic and another that differentiates. Meristems have three categories: apical, lateral, and intercalary.

Complete Answer:
- Meristems are clusters of cells that allow the essential body pattern established during embryogenesis to be reiterated and extended after germination. They divide to grant rise to at least one cell that continues to be meristematic and another that differentiates. Meristems have three categories: apical, lateral, and intercalary.
(I) Apical meristems: They occur at the growing shoot and root tips. Root apical meristems produce basis cap, which consists of lubricated cells. The meristem is pushed through the soil by organic process and elongation in additional proximal cells. Root meristems also can be derived secondarily from the stem of the plant. Shoot apical meristem produces stems, leaves, and reproductive structures.

(II) Lateral meristems: They are cylindrical meristems found in shoots and roots that end in secondary growth (an increase in stem and root girth by the assembly of vascular tissues). Monocot stems don't have lateral meristems, but often have intercalary meristems inserted within the stems between mature tissues.
- From lateral meristems, secondary growth increases the girth of the plant root or stem, instead of its length. Growth in plants occurs because the stems and roots lengthen. Some plants, that are woody, also increase in thickness during their lifetime.
- Primary growth is the results of cellular division within the shoot apical meristem whereas secondary growth is characterized by a rise in thickness or girth of the plant. It’s caused by biological processes within the lateral meristem. Some plant parts, like stems and roots, still grow throughout a plant’s life: a phenomenon called indeterminate growth.

(III) Intercalary meristems: It is made up of meristematic cells that divide mitotically in the stem at the base of nodes and leaf blades. Intercalary meristems are capable of cell division, and they allow for rapid growth and regrowth of many monocots. This is essential to these plant groups as it serves as an adaptive mechanism against herbivory. It plays a role in increasing the height of the plant, with the growth of internodes.

The secondary meristem is also responsible for giving rise to cells which differentiate into secondary permanent tissues of the plant. Being meristematic, the secondary meristem consists of undifferentiated, actively dividing cells. The cells are closely packed and as such intercellular spaces between cells are absent.

Therefore the correct option is B, radial growth.

Note: Annual Rings: The activity of the vascular cambium gives rise to annual growth rings. During spring season, cells of secondary xylem have an outsized internal diameter; their cell walls don't seem to be extensively thickened. This is often called early wood, or spring wood. In the autumn season, secondary xylem develops thickened cell walls, forming late wood, or autumn wood, which is denser than early wood. This alternation of early and late wood is due largely to a seasonal decrease within the number of vessel elements and a seasonal increase within the number of tracheids. It leads to the formation of an organic phenomenon, which might be seen as a circular ring within the cross section of the stem. An examination of the quantity of annual rings and also their nature reveal the age of the tree and the prevailing climate during each season.