Here's why:
* Guard cells need to be able to photosynthesize in order to generate energy for the active transport of potassium ions (K+) that drives the opening and closing of the stomata.
* Epidermal cells primarily act as a protective layer and do not need to photosynthesize. Their primary role is to protect the plant from water loss and environmental stress.
Therefore, chloroplasts are a key feature that distinguishes guard cells from other epidermal cells.
