Final answer:
In aqueous solutions, membrane lipids such as phospholipids spontaneously form micelles and bilayers, creating physical barriers that are essential for the structure and function of cells.
Step-by-step explanation:
When membrane lipids such as phospholipids are placed in an aqueous solution, they spontaneously form structures because of their amphipathic nature, meaning they have both hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails. Depending on the concentration and environmental conditions, phospholipids can form several different structures.
At lower concentrations and when heated in water, they often form micelles, which are tiny spheres where the hydrophilic heads face the water and the hydrophobic tails are hidden inside, away from the water. At higher concentrations, they may also form a bilayer, a structure that is the foundation of all cell membranes, with hydrophobic tails protected inside and hydrophilic heads facing the watery environment on either side.
This characteristic allows for the creation of a vital barrier that defines cell boundaries and encapsulates the cell's components.