What provides a boundary between the internal and external environment of all cells?

Question

Quizplus · Accepted Answer

The boundary between the internal and external environment of all cells is provided by a phospholipid bilayer, which consists of hydrophobic tails facing each other on the inside and hydrophilic heads facing outward on both sides. This arrangement allows the bilayer to be selectively permeable, controlling the entry and exit of substances into and out of the cell.

What Provides a Boundary Between the Internal and External Environment