Final answer:
In epithelial tissues, the most active cells are located at the basal layer, such as the basal cells in the stratum basale of the epidermis and the nuclei of columnar epithelial cells, which actively engage in absorption and secretion processes.
Step-by-step explanation:
In cells with many layers, particularly in epithelial tissues, the most active cells are typically located at the basal layer. For instance, in the epidermis, the basal cells residing in the stratum basale are responsible for proliferation and give rise to the different layers of skin as they differentiate and migrate upwards. These basal cells are foundational and continuously divide to replenish the skin's outer layers, which are regularly sloughed off.
Columnar epithelial cells, which are shaped like columns, are another example and are most often found in a single-layer arrangement. Their nuclei are aligned at the base of the cells, suggesting that the base is where a lot of cellular activities, like absorption and secretion, are concentrated. This is especially apparent in the digestive tract, where these cells absorb nutrients, or in the female reproductive tract, where they play a specific role in the functioning of the system.
Overall, the basal ends of epithelial cells are typically highly active and essential for the function and renewal of the tissue.