Table 7.3 Summary of transport processes in cells.
General process Nature of transport Examples Description Qualities
Passive Energy expenditure by the cell is not required. Substances exist in a gradient and move from areas of higher concentration toward areas of lower concentration in the gradient. Diffusion osmosis
Facilitated diffusion A fundamental property of atoms and molecules that exist in a state of random motion
Molecule binds to a carrier protein in membrane and is carried across to other side. Nonspecific Brownian movement
Movement of small uncharged molecules across membranes
Molecule specific; transport both ways
Transports sugars, amino, water
Active Energy expenditure is required.
Molecules need not exist in a gradient.
Rate of transport is increased.
Transport may occur against a concentration gradient. Carrier-mediated active transport
Group translocation
Bulk transport
Atoms or molecules are pumped into or out of the cell by specialized receptor; driven by ATP or other high-energy molecules.
Molecule is moved across membrane and simultaneously converted to a metabolically useful substance.
Mass transport of large particles, cells, and liquids by engulfment and vesicle formation. Transports simple sugar, amino acids, inorganic ions (Na+, K+)
Alternate system for transporting nutrient (sugar, amino acids)
Process is endocytosis; examples are phagocytosis and pinocytosis