(1) In addition, evidence has been provided for an active transport mechanism in the human intestinal mucosa.

(2) It is easy enough to assert that active transport across membranes occurs, but much harder to explain how.

(3) Active transport: This process is characterized by selectivity and saturability and requires energy expenditure the cell.

(4) Active transport appears to be limited to drugs structurally similar to endogenous substances.

(5) Active transport processes have been identified for various ions, vitamins, sugars, and amino acids.

(6) Drugs may cross a biologic barrier by passive diffusion, facilitated passive diffusion, active transport, or pinocytosis.

(7) It is highlighted that besides passive transport, dissolved metal transport into bivalves was involved in active transport coupled with ATP.

(8) Anything that interferes with the provision of energy will interfere with active transport.