Biology · Cell: The Unit of Life · NEET
| Energy needed | Active: yes, uses ATP | Passive: no energy used |
| Direction | Active: against the gradient (low to high) | Passive: down the gradient (high to low) |
| Carrier protein | Active: always needs a carrier (pump) | Passive: only facilitated diffusion needs one |
| NCERT example | Active: Na+/K+ pump | Passive: simple diffusion, osmosis |
The one difference NEET tests: energy. Passive transport does NOT use energy. Molecules simply move down the concentration gradient (from higher concentration to lower). Active transport DOES use energy (ATP) because it pushes molecules against the gradient (from lower to higher concentration). NCERT (Ch 8) states active transport is 'an energy dependent process, in which ATP is utilised', while passive transport happens 'without any requirement of energy'.
No. Passive transport needs zero ATP. The molecules are already moving in the natural direction, from a crowded (high) side to an empty (low) side, so the cell spends nothing. This is why simple diffusion, osmosis, and facilitated diffusion are all passive. If a question says a process needs NO energy, it is passive.
Active transport. 'Against the gradient' means from lower concentration to higher concentration, which is like pushing water uphill. This is unnatural, so the cell must spend ATP. The NCERT example is the Na+/K+ pump. If a NEET question says 'movement or accumulation of ions against their concentration gradient', the answer is always active transport.
Diffusion is passive. Simple diffusion moves neutral solutes down the gradient with no carrier and no energy. Osmosis (diffusion of water) is also passive. Even facilitated diffusion, which uses a carrier protein, is still passive because it does not use ATP and still moves molecules down the gradient. The carrier just helps polar molecules cross the lipid bilayer.
The Na+/K+ pump is the NCERT example. It pumps sodium (Na+) out and potassium (K+) into the cell against their gradients using ATP. This pump keeps the neuron membrane polarised (resting potential), which is why it links to the Neural Control chapter too. In the kidney, reabsorption of Na+ in the PCT is also active transport.
Polar molecules and ions cannot pass through the nonpolar lipid bilayer on their own, so they need a carrier (transport) protein of the membrane. When moving against the gradient, this carrier protein also acts as a pump and uses ATP energy to force the molecule to the more crowded side. So active transport = carrier protein + ATP + against the gradient.
No, this is a common trap. Both use a carrier protein, but facilitated diffusion is PASSIVE. It uses NO ATP and moves molecules DOWN the gradient. The protein is only a helper door for polar molecules, not a pump. Active transport is the only one that uses ATP and goes against the gradient. Protein use is not the deciding factor; ENERGY and DIRECTION are.
The main difference between active and passive transport across cell membrane is:
Movement and accumulation of ions across a membrane against their concentration gradient can be explained by
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Osmosis is passive. It is simply the diffusion of water across a membrane from higher water concentration to lower, needing no ATP.
In the NCERT NEET syllabus, yes. Active transport is defined as an energy-dependent process in which ATP is utilised, for example the Na+/K+ pump.
No. Large or polar molecules usually cannot cross freely. Small neutral solutes and water cross passively; ions and polar molecules need carrier proteins, and moving against the gradient needs active transport.
Facilitated diffusion is passive. It uses a carrier protein to help polar molecules cross, but it uses no ATP and still moves molecules down the gradient.
Energy. If a process uses ATP or moves against the gradient, it is active. If it uses no energy and moves down the gradient, it is passive.
