Phospholipids are the major component of biological membranes. \- When placed in aqueous solution, phospholipids spontaneously form lipid bilayers. \- According to the fluid-mosaic model, membrane phospholipids form lipid bilayers with membrane proteins associated with the bilayer as both peripheral and integral proteins.

Phospholipids are the major component of biological membranes and have a unique structure. They consist of a hydrophilic (water-attracting) phosphate head and two hydrophobic (water-repelling) fatty acid tails. This structural feature of phospholipids determines their behavior in an aqueous solution.

When placed in an aqueous solution, phospholipids spontaneously form lipid bilayers. This arrangement happens because the fatty acid tails attract each other, trying to hide from water molecules, while the phosphate heads are attracted to the water molecules. This interplay between hydrophobic and hydrophilic forces causes the phospholipids to form a bilayer, with the hydrophilic heads facing the aqueous environment and the hydrophobic tails facing inward, away from water.

The fluid-mosaic model is a widely accepted description of the organization of the biological membranes. According to this model, the lipid bilayer behaves like a fluid, where phospholipids and membrane proteins can freely move laterally (within the plane of the membrane). The mosaic part of the model refers to the diverse distribution of proteins and other molecules embedded within the bilayer or attached to its surface.

Membrane proteins are essential components of biological membranes. They carry out a wide range of functions, such as transport, signal transduction, and cell recognition. Based on their interaction with the bilayer, membrane proteins can be classified into two categories: peripheral and integral proteins. Peripheral proteins are loosely associated with the lipid bilayer, either indirectly through interactions with integral proteins or directly via weak electrostatic interactions with the phospholipid head groups. They can be easily removed from the membrane without damaging its structure. Integral proteins, on the other hand, are tightly embedded within the lipid bilayer. They usually contain one or more hydrophobic regions that interact with the hydrophobic tails of the phospholipids, keeping the protein anchored in the membrane. To remove integral proteins from the bilayer, the membrane structure must be disrupted, usually by using detergents. In summary, phospholipids form the lipid bilayer structure of biological membranes because of their amphipathic nature. The fluid-mosaic model describes the dynamic organization of these membranes, with peripheral and integral proteins having vital roles in maintaining the biological functionality of the membrane.