Final answer:
Collenchyma cells have unevenly thickened primary walls that support young, growing parts of the plant.
Step-by-step explanation:
Collenchyma cells have unevenly thickened primary walls that support young, growing parts of the plant. These cells are elongated and alive at maturity, usually found below the epidermis. An example of collenchyma cells can be seen in the 'strings' of a celery stalk.