**Core Concept:** Liposomes are artificial vesicles consisting of one or more lipid bilayers, which can encapsulate both hydrophilic and lipophilic substances. They are used in drug delivery, gene therapy, and as research tools in cell biology.

**Why the Correct Answer is Right:**
Liposomes are composed of phospholipids, which are naturally occurring molecules found in cell membranes. When phospholipids spontaneously form a bilayer, they create a vesicle that can encapsulate drugs or other molecules within its aqueous core or along the lipid bilayer. This property allows liposomes to deliver drugs more efficiently to target tissues or cells, thereby enhancing their therapeutic efficacy and reducing side effects.

**Why Each Wrong Option is Incorrect:**
A. This option is incorrect because liposomes are not simply "vesicles," as they are specifically designed phospholipid vesicles with potential drug delivery applications.
B. This option is wrong because liposomes are not "cellular structures" as they are artificial vesicles created from phospholipids.
C. This option is incorrect because liposomes are not "endocytosed immediately" by cells. Liposomes can be modified with targeting ligands to improve cellular uptake, but their interaction with cells is not always immediate.
D. This option is wrong because liposomes are not "eliminated rapidly" by the body; their clearance can be modulated by modifying their size, surface charge, or incorporating specific components into the liposomal composition.

**Clinical Pearl / High-Yield Fact:** Liposomes can serve as carriers for hydrophilic and lipophilic drugs, improving their pharmacokinetics and therapeutic effectiveness. By modifying liposomal surface properties, researchers can target specific tissues or cell types, enhancing treatment precision and reducing systemic side effects.