The correct option is Thin primary.
Explanation
Meristematic tissues consist of undifferentiated, actively dividing cells responsible for plant growth. Their structural characteristics are specifically adapted to facilitate rapid cell division and metabolic activity, distinguishing them from permanent tissues.
Detailed Analysis
- Thin Primary Walls (Correct): Meristematic cells possess a thin, elastic primary cell wall composed entirely of cellulose. This thinness and elasticity are essential to allow the cell to expand and divide during cytokinesis. A rigid wall would hinder the process of cell division and enlargement.
- Thick Secondary Walls (Incorrect): Secondary cell walls are laid down internal to the primary wall after cell growth has ceased. They provide rigidity and mechanical strength (as seen in sclerenchyma) but prevent the expansion required for dividing cells.
- Lignified (Incorrect): Lignification involves the deposition of lignin, which makes cell walls hard, impermeable, and rigid. This is characteristic of dead mechanical tissues (like sclerenchyma fibers or xylem vessels), not actively dividing living cells.
- Cutinised (Incorrect): Cutin is a waxy substance deposited on the outer walls of epidermal cells (forming the cuticle) to reduce water loss. It is not a characteristic of the internal dividing cells of the meristem.
Key Takeaway: Meristematic cells are characterized by thin, cellulosic primary cell walls, dense cytoplasm, prominent nuclei, and the absence of vacuoles or secondary wall thickening to support continuous cell division.