NEET 2023 Botany Question 123 Solution
Question
Movement and accumulation of ions across a membrane against their concentration gradient can be explained by
- (1)Active Transport
- (2)Osmosis
- (3)Facilitated Diffusion
- (4)Passive Transport
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Movement and accumulation of ions across a membrane against their concentration gradient can be explained by
Whenever solute transport occurs "against concentration gradient" (uphill) leading to accumulation inside the cell, it strictly requires metabolic energy (ATP) through Active Transport!
Transport mechanisms across biological membranes are categorized based on energetics and electrochemical directionality:
Because the concentration of essential mineral ions in root cortical cells is often 100 to 1000 times higher than in the surrounding soil solution, plants must actively pump ions inward across root cell membranes via membrane carrier proteins (proton-pumping ATPases).
NCERT states: "Active transport uses energy to pump molecules against a concentration gradient. Active transport is carried out by membrane-proteins... Active transport uses ATP."
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Accurate NCERT definition: movement against a concentration gradient requiring ATP is active transport.
Osmosis describes the passive diffusion of solvent (water) along its chemical potential gradient, not ion accumulation against a gradient.
Facilitated diffusion is passive; transport proteins move solutes downhill along concentration gradients without ATP.
Passive transport only proceeds down a chemical gradient from higher to lower concentration.
Both facilitated diffusion and active transport require specific membrane proteins. However, only active transport can move molecules uphill against a gradient.
"Active transport uses energy to pump molecules against a concentration gradient. It is carried out by specific membrane proteins."
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