Through these experiments, you concluded that:

1. The cells are organized into tissues. Each tissue provides a function that contributes to the function of the organ. In the skin, the epidermal tissue is composed of closely packed cells that serve as a protective barrier between the external environment and the body. The dermis serves to contain connective tissue and blood vessels needed to maintain the integrity of the epidermis. The subcutaneous layer contains fat cells important in keeping us warm. The lung has alveoli that are lined with a single layer of alveolar (epithelial) cells. This thin layer allows the lung to function by permitting easy oxygen and carbon dioxide exchange to occur between inhaled air and the blood. Finally, in the breast tissue you could see the organization of the glandular tissue cells to form the lobes and ducts needed to store and transport milk.

2. At this time, you cannot conclude how cells replenish themselves after normal wear and tear. However, it is likely to occur through cell division, which is regulated by the cell cycle.