Carrier ions like Na⁺ facilitate the absorption of substance like

• amino acids and glucose

• glucose and fatty acids

• fatty acids and glycerol

• fructose and some amino acids

A.

amino acids and glucose

Active transport occurs with the help of energy, usually against a concentration gradient. For this, cell membrane possess carriers and gated channels. Active transports of one substance are often accompanied by permeation of other substances. The phenomenon is called secondary active transport. It is of two main types- Co-transport (eg, glucose and some amino acid along with inward pushing of excess Na⁺) and counters transport (Ca²⁺ and H⁺ movement outwardly as excess Na⁺ passes inwardly).