Active Transport
செயலில் உள்ள கடத்தல்
Stop confusing diffusion with active transport. Diffusion is passive; it costs nothing. Active transport is the metabolic tax your cells pay to maintain homeostasis against a concentration gradient.
The idea
Active transport involves the movement of molecules across the membrane against the concentration gradient. This process requires energy in the form of ATP. Specific membrane proteins act as pumps to facilitate this movement. This is essential for maintaining ion gradients, such as the sodium-potassium pump.
Why it matters
It allows cells to accumulate essential nutrients or expel waste even when concentrations are unfavorable.
NEET lens
NEET focuses on the 'against the gradient' and 'ATP-dependent' keywords. Never confuse this with facilitated diffusion, which is also protein-mediated but passive. Memorize that active transport is unidirectional and highly selective.
Clinical significance
Failure of the Na+/K+ pump leads to cellular swelling and eventual necrosis. This mechanism is the primary target of cardiac glycosides like digoxin, used to treat heart failure by increasing intracellular calcium.
Introduction
Active transport is the movement of substances across a membrane against their concentration gradient, requiring energy (ATP) and specific carrier proteins (pumps).
Core concept
Features: against concentration gradient (low to high), requires ATP energy, uses specific protein pumps, selective (specific substances). Examples: Na⁺/K⁺ ATPase pump (3 Na⁺ out, 2 K⁺ in per ATP), proton pump (H⁺ pump), Ca²⁺ pump. Secondary active transport: uses gradient established by primary AT (glucose-Na⁺ cotransporter).
Go deeper
Na⁺/K⁺ ATPase: maintains ~10x higher K⁺ inside cell, ~10x higher Na⁺ outside. This creates the resting membrane potential. Uses ~30% of cell's ATP. Inhibited by ouabain (cardiac glycoside) — basis of digitalis toxicity.
From Class 10
You know substances move across membranes. Simple diffusion goes with concentration gradient. Active transport goes against it, requiring energy.