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Question
Annual rings and growth rings are formed due to the fluctuations in the activity of
Annual rings and growth rings are formed due to the fluctuations in the activity of
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Solution
The correct option is D Cambium
A growth layer in secondary xylem seen in a cross section of a woody stem or branch. A tree ring is simply a layer of wood produced during one tree's growing season. Each tree ring marks a line between the dark late wood that grew at the end of the previous year and the relatively pale early wood that grew at the start of this year.
One annual ring is composed of a ring of early wood and a ring of late wood. The growth occurs in the cambium (the thin, continuous sheath of cells between bark and wood). In spring, the cambium begins dividing. This creates new tissue and increases the diameter of the tree at two places - 1. Outside the cambium. The outer cells become part of the phloem. The phloem carries food produced in the leaves to the branches, trunk, and roots. Some of the phloem dies each year and becomes part of the outer bark.
2. Inside the cambium. The inner cells become part of the xylem. These cells contribute most of a tree's growth in diameter. The xylem carries water and nutrients from the roots to the leaves. These cells show the most annual variation. When a tree grows quickly, the xylem cells are large with thin walls. This early wood or springwood is the lighter-colored part of a tree ring. In late summer, growth slows; the walls of the xylem cells are thicker. This late wood or summerwood is the darker-colored part of a tree ring. So, annual rings and growth rings are formed due to the fluctuations in the activity of cambium and not because of xylem and phloem.
Therefore, the correct answer is option D.
A growth layer in secondary xylem seen in a cross section of a woody stem or branch. A tree ring is simply a layer of wood produced during one tree's growing season. Each tree ring marks a line between the dark late wood that grew at the end of the previous year and the relatively pale early wood that grew at the start of this year.
One annual ring is composed of a ring of early wood and a ring of late wood. The growth occurs in the cambium (the thin, continuous sheath of cells between bark and wood). In spring, the cambium begins dividing. This creates new tissue and increases the diameter of the tree at two places - 1. Outside the cambium. The outer cells become part of the phloem. The phloem carries food produced in the leaves to the branches, trunk, and roots. Some of the phloem dies each year and becomes part of the outer bark.
2. Inside the cambium. The inner cells become part of the xylem. These cells contribute most of a tree's growth in diameter. The xylem carries water and nutrients from the roots to the leaves. These cells show the most annual variation. When a tree grows quickly, the xylem cells are large with thin walls. This early wood or springwood is the lighter-colored part of a tree ring. In late summer, growth slows; the walls of the xylem cells are thicker. This late wood or summerwood is the darker-colored part of a tree ring. So, annual rings and growth rings are formed due to the fluctuations in the activity of cambium and not because of xylem and phloem.
Therefore, the correct answer is option D.
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