Final answer:
Parenchyma cells are the common plant cells that can assume various shapes and sizes and often have 14 sides. They are responsible for metabolic functions like photosynthesis and can store starch and other secretions.
Step-by-step explanation:
Plant cells that are very common in plants and assume various shapes and sizes, with most of them having 14 sides, are called parenchyma cells. Some examples of plant parts where parenchyma cells are found include the stem, root, inside of the leaf, and the pulp of the fruit. These cells are responsible for metabolic functions like photosynthesis and can also store starch and other substances such as oils and tannins.