Here's why:

* Plant cells have a rigid cell wall made of cellulose, which gives them their rectangular or boxy shape. They also have chloroplasts for photosynthesis and a large central vacuole for storage and support.

* Animal cells lack a cell wall and chloroplasts. Their structure is more flexible, often appearing round or irregular. They have smaller vacuoles and may contain centrioles for cell division.

While both animal and plant cells have some common components like a cell membrane, cytoplasm, and nucleus, their overall shape and internal structures are distinct due to their different functions and adaptations.