Question

Which meristem is responsible for increase in girth of stem/root? ____.

• A. Apical meristem
• B. Intercalary meristem
• C. Lateral meristem
• D. Primary meristem

Hint:

To easily remember: "Apical" is at the apex/top (Length), "Intercalary" is at the intervals/nodes (Regrowth), and "Lateral" is at the sides (Girth/Width).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Plant growth occurs in two distinct axes: elongation (height) and expansion (girth). Specialized regions of actively dividing cells called meristems direct these growth patterns.

Step 2: Detailed Explanation:
The tissues responsible for the secondary growth (increase in thickness or girth) of a plant stem or root are the lateral meristems. These meristems lie parallel to the lateral sides of the stem and roots. When their cells divide, they produce secondary xylem, secondary phloem, and cork tissue, widening the plant structure. Examples include the vascular cambium and cork cambium.
• Apical meristems are located at the tips of stems and roots and increase the plant's length.
• Intercalary meristems are located at the nodes or leaf bases, primarily helping in internodal elongation.

Step 3: Final Answer:
The lateral meristem is responsible for the increase in the girth of a stem or root.

Answer 2

This question is about which meristem widens a stem or root over time, so we need to trace what each meristem type actually produces: new length, replacement tissue, or extra layers around the existing structure.

1. Apical meristem: sits at the very tip of roots and shoots and is responsible for the plant growing taller or the root growing deeper, a lengthwise (primary) growth pattern that does not add width.
2. Intercalary meristem: occurs at nodes or the base of leaves, most notably in grasses, and functions mainly to restore length after the tip is grazed or cut, again a lengthening role rather than a widening one.
3. Lateral meristem: lies parallel to the long axis of the stem or root, for instance the vascular cambium and cork cambium, and produces new secondary xylem, phloem, and cork with each division, physically thickening the organ. This continuous addition of layers around the circumference is exactly what girth increase means.
4. Primary meristem: is the general term for meristem tissue involved in a plant's initial, first-season growth, and by itself does not specify any width-increasing activity.

Only the meristem that adds material around the existing structure, rather than at its tip or base, can be responsible for a stem or root becoming thicker.

Therefore, the correct answer is Lateral meristem.