Final answer:
To reach the cytosol, large molecules require vesicle transport, which includes endocytosis and exocytosis, forms of active transport that need energy. Endocytosis brings substances into the cell, while exocytosis moves them out. Smaller molecules might use facilitated transport, but not for crossing into the cytosol from outside the cell.
Step-by-step explanation:
In order to reach the cytosol, large molecules and particles that cannot pass through the plasma membrane via passive means need to be transported through vesicle transport. This type of transport includes two processes: endocytosis and exocytosis. Both of these processes are forms of active transport that require energy, typically in the form of ATP (adenosine triphosphate).
During endocytosis, substances outside the cell are engulfed by the plasma membrane, which forms a vesicle around the substance and brings it into the cell. Conversely, exocytosis involves the fusion of vesicles containing substances with the plasma membrane, leading to the release of the vesicle's contents outside of the cell. This mechanism is essential for the transport of proteins, hormones, and neurotransmitters, among other substances.
Some substances can also enter the cell through facilitated transport, which is the movement down a concentration gradient through specific protein channels, but this is typically for smaller molecules that do not require vesicle transport. Active transport is necessary when substances need to move against the concentration gradient or when the substances are too large to fit through the channels meant for facilitated transport.