Final answer:
Parenchyma cells are the specialized plant cells that are loosely packed and cube-shaped, playing a key role in photosynthesis, wound healing, and storage in various parts of plants including leaves.
Step-by-step explanation:
The specialized plant cell that is loosely packed and cube shaped is known as the parenchyma cell. Parenchyma cells are responsible for metabolic functions such as photosynthesis, help with the repair and healing of wounds, and some may store starch. In the context of leaf structure, parenchyma cells make up the spongy mesophyll, a layer with loosely arranged, irregularly shaped cells that allow for gaseous exchange between the leaf and the outside atmosphere through stomata. These cells have primary cell walls which are less rigid compared to secondary cell walls, allowing for flexibility and the maintenance of plant structure when cells are alive and hydrated.