Active transport occurs with the help of energy, usually against concentration gradient. For this, cell membrane possesses carriers and gated channels. Active transports of one substance is 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 acids along with inward pushing of excess $\mathrm{Na}^{+}$) and counter transport $\left(\mathrm{Ca}^{2+}\right.$ and $\mathrm{H}^{+}$movement outwardly as excess $\mathrm{Na}^{+}$passes inwardly).