Final answer:
The nail matrix is the active tissue responsible for generating cells that harden to form the nail as they move outward from the root to the nail.
Step-by-step explanation:
The active tissues that generate cells which harden as they move outward from the root to the nail are called the nail matrix. The nail matrix is a deep layer of epidermal tissue located at the proximal end of the nail, where nail growth occurs. It contains stem cells that divide to produce new cells. As new cells are added, the nail grows, and these cells harden as they become integrated into the nail plate, the main keratinous plate that forms the nail. The process of nail growth includes the formation of the nail root and the extension of the nail plate as the cells progressively harden and move outward.
The three main parts of a nail are the root, plate, and free margin. The nail bed is situated beneath the nail plate, and it's rich in blood vessels giving the nail its pink color, while the lunula, or 'little moon,' is a crescent-shaped region at the base of the nail. These components work together to continuously produce and support the structure of the nail.