A vesicle is a small bubble enclosed by lipid bilayer. Vesicles can form naturally, for example, during the endocytosis, or they may be prepared. Artificially prepared vesicles are known as liposomes. If there is only one phospholipid bilayer, they are called unilamellar vesicles; otherwise they are called multilamellar.

Vesicles do many things. The membrane enclosing the vesicle is similar to that of the plasma membrane, and vesicles can fuse with the plasma membrane to release their contents outside of the cell. Vesicles can also fuse with other organelles within the cell.

Because it is separated from the cytosol, the inside of the vesicle can be made to be different from the cytosolic environment. For this reason, vesicles are a basic tool used by the cell for organizing cellular substances. Vesicles are involved in metabolism, transport, buoyancy control, and enzyme storage. They can also act as chemical reaction chambers.

Vacuoles are vesicles which contain mostly water.

Secretory vesicles contain materials that are to be excreted from the cell. Cells have many reasons to excrete materials. One reason is to dispose of wastes. Another reason is tied to the function of the cell. Within a larger organism, some cells are specialized to produce certain chemicals. These chemicals are stored in secretory vesicles and released when needed. Some examples include the following.

Vesicle may refer to:

Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines. Among the most important topics are five unifying principles that can be said to be the fundamental axioms of modern biology:

Subdisciplines of biology are recognized on the basis of the scale at which organisms are studied and the methods used to study them: biochemistry examines the rudimentary chemistry of life; molecular biology studies the complex interactions of systems of biological molecules; cellular biology examines the basic building block of all life, the cell; physiology examines the physical and chemical functions of the tissues, organs, and organ systems of an organism; and ecology examines how various organisms interact and associate with their environment.

The term biology is derived from the Greek word βίος, bios, "life" and the suffix -λογία, -logia, "study of." It appears in German (as biologie) as early as 1791, and may be a back-formation from the older word amphibiology (meaning the study of amphibians) by deletion of the initial amphi-.