Final answer:
The phospholipid bilayer has two leaflets due to the amphipathic nature of phospholipids, which arrange hydrophilic heads outward and hydrophobic tails inward, creating a barrier. It allows the integration of proteins, maintains homeostasis, and forms lipid rafts for cellular processes.
Step-by-step explanation:
These molecules have hydrophilic heads that are attracted to water and hydrophobic tails that repel water. When phospholipids are in an aqueous environment, they arrange themselves so that the hydrophilic heads face the water on the outside and inside of the cell, while the hydrophobic tails face each other on the inside of the bilayer, creating a barrier that is impermeable to most water-soluble substances. This structure serves several critical functions. Primarily, it provides a barrier (C) between the extracellular and intracellular environments, which allows cells to maintain homeostasis by controlling the substances that enter and leave the cell. Furthermore, it allows for the integration of integral membrane proteins (B), which perform various functions such as transport, communication, and catalysis. These proteins can embed within the bilayer due to their fluid nature, which is supported by the presence of cholesterol and other lipids. Lastly, the bilayer contributes to the formation of lipid rafts (D), which are specialized areas in the membrane where lipids, proteins, and other molecules are more tightly packed and involved in specific cellular processes.