Question

Annual ring are found in plants belonging to
A. Arabic regions
B. Temperate areas
C. Tropics
D. Near sea beaches

Answer 1

Hint:- Higher plants undergo two types of growth during their lifespan namely- primary growth and secondary growth. The growth that occurs in the earlier life stages of a plant is referred to as primary growth. An increase in the length of the plant body occurs during primary growth. The growth that takes place in the later life stages of a plant is referred to as secondary growth. An increase in girth or circumference of the plant body occurs during secondary growth.

Complete solution:-
Meristematic tissue (actively dividing tissue) are of three types- apical meristem, intercalary meristem, and lateral meristem. Lateral meristem occurs on the lateral side of plant organs. The activity of the lateral meristem increases the circumference of the plant organ. Lateral meristem is of both primary and secondary origin.
The primary lateral meristem is called intrafascicular cambium and the second lateral meristem includes interfascicular cambium. During secondary growth, the parenchymatous cells present in the lining of intrafascicular cambium become meristematic and form interfascicular cambium as a secondary meristem by the process called dedifferentiation. Both the cambiums unite with each other to form a circular ring of cambium.
Cambium consists of two types of cells namely- fusiform initials and ray initials. The fusiform initials form secondary xylem and secondary phloem, whereas the ray initials form the secondary medullary rays. The rings of secondary xylem take about one year to complete, therefore these rings of secondary xylem are known as annual rings.
The activity of cambium is temperature-dependent and is directly proportional to temperature. In tropical regions there occurs no seasonal variations (constant temperature remains throughout the year). Thus the annual rings are indistinctly formed. But in temperate regions, seasonal variations are well marked and thus fluctuating temperature remains throughout the year. Thus distinct annual rings are found in plants of these areas.

Thus, the correct answer is option B.

Note:- Distinct annual rings contain two types of woods namely- early or springwood and late or autumn wood. Both these growth rings together form the annual ring. The age of a plant can be calculated by counting the total number of annual rings formed in it. Since the maximum number of annual rings are found in the basal regions of woody plants, therefore annual rings of the basal region are counted to determine the age of the plant.