Final answer:
Whether amphipathic molecules form micelles or lipid bilayers depends on their structure; single-tailed molecules form micelles, while double-tailed phospholipids form bilayers which are essential for cell membrane integrity.
Step-by-step explanation:
The formation of micelles or a lipid bilayer by amphipathic molecules in aqueous solutions depends largely on the shape and structure of these molecules. Micelles are typically formed by molecules with a single hydrophobic tail and a hydrophilic head, resulting in a spherical shape with tails in the center and heads facing the water.
In contrast, phospholipids, which have two hydrophobic tails, tend to form a lipid-bilayer sheet or sphere, with the tails sandwiched in the center away from water and the hydrophilic heads facing the water on both sides. This bilayer structure is fundamental for the formation of cell membranes, providing a barrier that separates the internal cellular environment from the external aqueous surroundings.