Final answer:
Many cells undergo mitosis in the onion root tip because it encompasses the apical meristem, a dynamic tissue responsible for root growth. Growth factors like auxin and brassinosteroids regulate the cell division process, with auxin promoting it at higher concentrations near the root tip.
Step-by-step explanation:
There are many cells undergoing mitosis in the onion root tip because this region contains the apical meristem, a zone of undifferentiated cells that is responsible for the growth of the root lengthwise. These meristematic cells undergo rapid cell division, and the highest frequency of mitosis can be observed just behind the root cap. The root cap serves to protect the delicate apical meristem as it pushes through the soil.
As you move away from the tip of the root, the cells' purpose changes. They begin to elongate, mature, and take on specialized functions. Growth factors like auxin and brassinosteroids regulate the process of cell division in the root tips. Auxin concentrations are higher near the root tip and stimulate cell division, while brassinosteroids, which have limited transport between cells, decrease in concentration near the root cap.
In summary, the onion root tip is a zone of active cell division due to the presence of apical meristem and the influence of growth factors. This cell division is crucial for root growth as it allows the plant to access additional resources such as water and minerals from the soil.