Answer:
Growth of a plant begins with a seed. Respiration (energy released from foods for life processes) is a sign of activity in the seed. Actual germination or breaking of seed dormancy, however, does not begin until water is absorbed by the seed. The moisture content of the seed must be at least 9 percent before germination begins. Certain enzymes (chemicals that help cause other chemicals to react) are activated and respiration speeds up. The enzymes begin breaking down the stored food (or starch) for energy to be used in cell division. Exactly what triggers cell division is not completely understood. Some botanists think growth hormones may play a major role in the first stages of germination.
The root tip begins elongating, followed by the shoot tip elongation. The active meristem (a zone of dividing cells that continues to add cells to the plant body as long as the plant is growing) of the root tip is covered and protected by a cap of cells. This cap continues to slough off cells and to be replaced as the root grows through the soil by adding more and more cells to the root tips. Every cell of the root originates from the meristem. Examined under a microscope, the dividing root cells appear to look the same as the dividing shoot cells. In fact the meristematic cells of a carrot are not easily distinguished from those of an oak tree or an onion, except for the chromosome number. Only the DNA message in the chromosomes of the meristematic cells appears to be different. The DNA of carrot meristems sends the chemical messages to the rest of the cell to prepare to become a carrot. Other than DNA and heredity, scientists are still looking for answers as to why dividing carrot cells produce a carrot and not an oak tree. After cell division in the meristems, cells undergo elongation before they begin to differentiate. Cells produced by the root and shoot tip meristems become the primary tissues or first forward tissues of the plant body.
Differentiation. Each species of plant has a unique pattern of development. The dividing cells of the root tip begin to increase in length and continue to elongate until they are several millimeters behind the root tip and the meristem that produced them. The root tip continues to divide and push through the soil farther away from the elongating cells. Where elongation in the root stops, differentiation begins. Cells differentiate when they begin to take on different shapes and functions. Some will become parenchyma for storage; others will become cells of the phloem or xylem for conduction of food and water. At specific locations a nest of cells may start elongating in a crosswise direction to the other cells of the root axis. This nest of cells with its own meristematic cells may form a branch root. If we are looking at a developing stem, the nest of cells may develop into a branch or a leaf. Leaves and roots do not occur just anywhere in development, but form a pattern with other leaves or roots already developed. The leaf has many different growth rates. Cells near the tip of a leaf stop dividing and elongating before those near the center and base of the leaf.
Growth information helps us to understand how the plant in the seed increases in size both above and below ground, but how do plants increase in girth or tree trunks get wider?
Differentiation. Many types of plant cells may develop from a meristematic cell.
Step-by-step explanation:
differentiation: The maturation of a cell produced by a plant meristem; cells may mature to form fibers, parenchyma, vessel members, etc.
elongation: In the maturation process of cells, the first step after production by a meristem; a lengthening of the cell assisted by water intake in living things to occur; an organic catalyst.
meristem: The youthful, undifferentiated cells of root and shoot tips and other plant parts that produce new cells for growth in size and girth.
vascular cambium: The meristematic cells which produce new cells increasing plant body girth; often forming a ring only several cell layers wide in woody stems and roots.