Q.Name the three sequential phases through which a plant cell derived from an apical meristem normally passes as it becomes a mature, specialised cell.

A cell derived from a root or shoot apical meristem passes through three overlapping phases on its way to becoming a mature, functional cell. In the meristematic phase, at the very apex, cells are small, densely cytoplasmic, thin-walled and actively dividing. In the elongation phase, immediately behind the meristem, cells stop dividing and instead enlarge considerably, chiefly through water uptake into an expanding central vacuole, with new cell wall material deposited to accommodate the increase in volume; this phase contributes most of a growing organ's visible lengthening. In the maturation phase, enlargement stops, the protoplasm is proportionally reduced as the vacuole comes to dominate the cell's volume, and the cell wall is often further thickened and chemically specialised (for example, lignified in a xylem vessel element), as the cell settles into its final, specific, mature form.