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Biology Question 103 – NEET-UG 2023

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Movement and accumulation of ions across a membrane against their concentration gradient can be explained by

Membrane transport mechanisms are broadly classified into passive and active processes based on energy requirement and movement relative to the concentration gradient.

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Ninja Strategy•Key Term Analysis: 'Against Concentration Gradient'

Recognize that 'against concentration gradient' is the defining characteristic of active transport, immediately eliminating all passive transport options.

Step 1: Analyze the Question Statement✦ Active

The question describes the "Movement and accumulation of ions across a membrane against their concentration gradient." The key phrase here is "against their concentration gradient."

Step 2: Identify the Energy Requirement○ Expand

Movement of substances against their concentration gradient (from a region of lower concentration to a region of higher concentration) requires an input of cellular energy, typically in the form of ATP.

Step 3: Match with Transport Mechanisms○ Expand

1. **Osmosis** is the movement of water across a semipermeable membrane, a passive process. 2. **Facilitated Diffusion** is a type of passive transport where substances move down their concentration gradient with the help of membrane proteins, without direct energy expenditure. 3. **Passive Transport** is a general term for movement down the concentration gradient, not requiring cellular energy. 4. **Active Transport** is the process that moves substances across a membrane against their concentration gradient, requiring metabolic energy.

💡 Teacher's Secret Hint

Remember that passive transport always occurs down the concentration gradient, while active transport can move substances against it.

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