Final answer:
Active transport involves the movement of substances against their concentration gradient requiring energy, primarily ATP. Primary active transport directly utilizes ATP, whereas secondary active transport does not, instead using the electrochemical gradients established by primary transport to move substances.
Step-by-step explanation:
Characterization of Active Transport
Active transport is the movement of molecules across a cell membrane from an area of lower concentration to an area of higher concentration, against the concentration gradient. Unlike passive transport, which relies on the kinetic energy of molecules moving down their concentration gradient, active transport requires cellular energy, usually in the form of ATP. This process is vital for maintaining homeostasis within the cell by regulating the internal composition of ions and molecules.
Primary vs. Secondary Active Transport
Primary active transport directly uses energy from ATP to pump molecules against their gradient. A hallmark example of this is the sodium-potassium pump which exchanges three sodium ions out of the cell for two potassium ions into the cell, thus maintaining an electrochemical gradient.
Secondary active transport, on the other hand, does not directly utilize ATP. Instead, it harnesses the energy from the electrochemical gradients created by primary active transport to move substances across the cell membrane. Examples include the transport of glucose and amino acids, which often occur simultaneously as ions like sodium are moved back into the cell down their gradient established by the sodium-potassium pump.
While both types of transport are active because they require energy, their main difference lies in their energy sources; primary active transport uses ATP directly whereas secondary active transport relies on energy stored in ion gradients.