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 remember which meristem does what:
- Apical and Intercalary = length (primary growth).
- Lateral = girth/thickness (secondary growth).

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify the type of meristematic tissue responsible for the increase in the diameter (girth) of a plant stem or root. This is a repeat of a previous question, confirming the importance of this concept.

Step 3: Detailed Explanation:
Meristematic tissues are plant tissues where cells continuously divide to produce new cells. They are classified based on their position and function:
1. Apical meristem: Located at the tips of roots and shoots. Responsible for primary growth, which increases the length of the plant.
2. Intercalary meristem: Located at the base of internodes and leaves, particularly in monocots. Also responsible for primary growth (lengthening).
3. Lateral meristem: Consists of the vascular cambium and cork cambium. These meristems are responsible for secondary growth, which increases the girth or thickness (diameter) of the stem and root.
4. Primary meristem: A general term for meristems that contribute to primary growth (increase in length).
Therefore, lateral meristems are directly responsible for the increase in plant girth.

Step 4: Final Answer:
Lateral meristem is responsible for increase in girth of stem/root.

Answer 2

This question, worded slightly differently from a similar one earlier in the paper, still asks which meristem thickens a stem or root, so each option is checked for whether it lengthens or widens the plant axis.

1. Apical meristem: Sitting at root and shoot tips, this tissue is responsible for the plant growing taller or the root pushing further into the soil - length, not width.
2. Intercalary meristem: Found between mature tissue, commonly near the base of grass leaves, this also produces length increase, letting a mown lawn regrow quickly, without adding thickness.
3. Lateral meristem: This consists of the vascular cambium (between xylem and phloem) and cork cambium (near the surface). Both divide parallel to the long axis of the stem or root, continually adding tissue on either side of themselves, which is precisely what widens the axis over a growing season.
4. Primary meristem: This is a broad label covering meristems that trace back to the embryonic apical regions, and everything under that label produces length increase, not girth.

Girth increase, by definition, is a widening process, and only the lateral meristem's cambium layers add tissue outward from the plant's central axis.

Therefore, the correct answer is Lateral meristem.