Final answer:
Vesicles are small compartments that are separated from the cytosol by a lipid bilayer. They are formed to avoid barriers and play important roles in organizing molecules in the cell. Vesicles can be chemically different from the cytosol and are used in processes like phagocytosis.
Step-by-step explanation:
The spontaneous closure of a planar bilayer into a vesicle is a way to avoid barriers from the water and other materials on the other side. Vesicles are small, spherical compartments that are separated from the cytosol by at least one lipid bilayer. They are formed from parts of the cell membrane or made in the Golgi apparatus and endoplasmic reticulum.
Vesicles are important for organizing metabolism, transport, and storage of molecules in the cell. They can be chemically different from the cytosol and are used as chemical reaction chambers. The composition of the vesicle's surface differs from that of the bulk, allowing it to avoid barriers and maintain stability.
For example, when preparing for phagocytosis, a portion of the plasma membrane becomes coated with proteins, which stabilize the membrane and eventually enclose the particle in a vesicle. The contents of the vesicle can later be broken down or released into the extracellular fluid.