The structure common to both plant and animal cells is the cell membrane.

Here's why:

* Cell membrane: This is the outer boundary of the cell, responsible for controlling what enters and exits. It's essential for all living cells to maintain their internal environment and interact with their surroundings.

While both plant and animal cells have a cell membrane, they have other structures that differ. Plant cells have cell walls, chloroplasts, and large vacuoles, which animal cells lack.