A plant cell consists of a cell wall, chloroplast and vacuoles that makes it different from the animal cell. 
For a plant cell to elongate, two things that facilitates the process are light and phytohormones. It occurs when individual cells and group of cells grow longer. 
In order for a plant cell to elongate, two things that must occur are:
1. temporary loosening of cell wall
2. pumping hydrogen ions across the cell membrane.