Final answer:
Parenchyma cells form most of the inside of a plant, performing essential metabolic functions, wound healing, and storage of nutrients across different parts like the stem, root, and fruit.
Step-by-step explanation:
The cell types that form most of the inside of a plant are parenchyma cells. These cells are found throughout the plant's body, including the stem, root, inside of the leaf, and the pulp of the fruit. Parenchyma cells carry out a variety of functions imperative to the plant's well-being, such as photosynthesis, storage of starch, and the healing of wounds. In a stem's cross-section, the cortex and the central pith are typically made up of parenchyma cells. It's worth noting that while sclerenchyma, collenchyma, and epidermal cells also play crucial roles in the plant structure, parenchyma cells are the most abundant and versatile.