Question

which model best represents the lipid bilayer of a cell membrane?
extracellular environment
(outside the cell)
extracellular environment
(outside the cell)
intracellular environment
(inside the cell)
intracellular environment
(inside the cell)
extracellular environment
(outside the cell)
extracellular environment
(outside the cell)
intracellular environment
intracellular environment

Explanation:

The lipid bilayer of a cell membrane consists of phospholipids. Each phospholipid has a hydrophilic (water - attracting) head (represented by blue circles) and a hydrophobic (water - repelling) tail (represented by the orange, wavy structures). In the lipid bilayer, the hydrophilic heads face the aqueous environments (extracellular and intracellular), and the hydrophobic tails face each other, forming a double - layer structure. Looking at the options, the top - left model (assuming the first model in the top - left corner of the four - model layout) has the hydrophilic heads (blue circles) facing the extracellular (top) and intracellular (bottom) aqueous environments, and the hydrophobic tails (orange) in between, which matches the structure of the lipid bilayer.

Answer:

The model in the top - left (with hydrophilic heads facing extracellular and intracellular environments, and hydrophobic tails in between) best represents the lipid bilayer of a cell membrane.