Why do we need cotransport?

Question

Why do we need cotransport?

Answer 1

To get molecules or ions into a cell against its concentration gradient (low to high)

A cotransporter is an integral membrane protein that is involved in secondary active transport. It works by binding to two molecules or ions at a time and using the gradient of one solute's concentration to force the other molecule or ion against its gradient (ie. up the concentration gradient of sucrose).

Eg.Proton-sucrose cotransporters are common in plant cell membranes. An ATP molecule in the cell phosphorylates a carrier protein, causing a conformational change that shuttles a proton across the membrane. The proton binds with sucrose in the extracellular fluid, then undergoes passive transport down its concentration gradient.