Final answer:
Materials are carried in a cell by vesicle transport, an active transport mechanism utilizing vesicles to move substances across the plasma membrane, involving energy expenditure.
Step-by-step explanation:
Materials are carried in a cell by the mechanism of vesicle transport, a type of active transport where substances are transported across a cell membrane using vesicles. During this process, the material to be transported initially attaches to protein or glycoprotein receptors on the outer surface of the plasma membrane. The substances are then handed off to specific integral proteins that help facilitate their movement across the membrane. Some of these integral proteins form channels made of beta-pleated sheets, while others are carrier proteins that assist in diffusing the substance through the membrane.
In the case of large molecules like proteins that cannot pass directly through the plasma membrane, vesicle transport is crucial. This type of active transport requires energy and includes two variants: endocytosis (where materials are brought into the cell within vesicles) and exocytosis (where materials are expelled from the cell within vesicles). Facilitated transport is another method, although it occurs by diffusion without energy expenditure, helping polar molecules or ions cross the plasma membrane with the help of facilitated transport proteins that shield them from the hydrophobic interior of the membrane.