Plant growth

Cell expansion and growth occurs very differently in plants than it does animals. Animals tend to produce unique organs with specific cells for each organ, whereas plant growth is iterative and will generate many of the same organs. Stem cell tissue in plants is known as meristem and contains undifferentiated cells. There is a shoot apical meristem and root apical meristem both of which are responsible for primary growth, such as new leaves, flowers, and roots. The other kind of meristem found in the cambium is responsible for the growth of bark, xylem, and phloem. The basic structure of the apical meristems is a stacked one. The first level is at the apex of the meristem and consists of the newly dividing cells; the second level just below is where cell elongation takes place; underneath it, the third level is where cell differentiation occurs; and the last level below that is where mature cells are located. The cell division layer leads to the creation of new cells with primary cell walls that will generate leaves and flowers. The second level during which cell elongation occurs is a dynamic layer. Plant cells have the capacity to increase their solute potential by generating an electrostatic gradient that powers active transport channels that move metabolites and ions in the cell. Water can then enter the plant cells via osmosis or aquaporins. This raises the internal pressure of the plant cell - known as turgor pressure - which pushes against the primary cell wall causing it to expand. Some parts of the primary wall are less rigid than others, causing directional expansion, usually lengthwise. Eventually the pressure exerted on the primary cell wall equalizes with the pressure the wall exerts on the cell’s plasma membrane and expansion comes to a halt. At this point, the cells will begin to differentiate by synthesizing a variety of secondary cell walls that will determine their purpose. Once this process is done, the cells have fully differentiated and can now form the new organs of the plant.