Final answer:
Active transport requires a carrier protein to move substances across the cell membrane using ATP, against their concentration gradient. This process is vital for maintaining necessary concentrations of ions and molecules within the cell, crucial for proper cell function.
Step-by-step explanation:
Active transport cannot occur without assistance. A carrier protein is always required in this process; a protein in the membrane carries the molecules across the membrane against their concentration gradient.
During active transport, cells use ATP (adenosine triphosphate) as energy to move substances through the plasma membrane. This is often carried out with the help of these carrier proteins or pumps, which can move molecules from an area of low concentration to one of high concentration, effectively going against the natural diffusion process.
There are three main types of carrier proteins involved in active transport: uniporters, symporters, and antiporters. Uniporters carry one specific ion or molecule, while symporters and antiporters can carry two, but in the same or opposite directions, respectively. These proteins are crucial for maintaining the right concentration of ions and molecules inside cells, which is necessary for various cellular functions. For example, neurons depend on protein pumps to transmit signals by moving ions via active transport.