Question

both prokaryote and eukaryote cells have this structure. it helps maintain homeostasis and is a boundary between the inside of the cell and the outside environment. it is the
a nucleus.
b membrane.
c cytoplasm.
d cell wall.

Explanation:

The cell - membrane is present in both prokaryotic and eukaryotic cells. It acts as a boundary between the cell's interior and the external environment and helps maintain homeostasis by regulating the movement of substances in and out of the cell. The nucleus is only in eukaryotes, the cytoplasm is not a boundary structure in the sense described, and not all prokaryotes and eukaryotes have a cell - wall (e.g., animal cells don't have a cell - wall).

Answer:

B. membrane