Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R:
Assertion (A): Ionic gradients across the resting axonal membrane are maintained by the active transport of ions by the sodium-potassium pump.
Reason (R): Sodium potassium pump transports 3Na+ inwards for 2K+ outward the cell.
In the light of the above statements, choose the correct answer from the options given below:
A is true but R is false.
— Concept: This question tests your understanding of the resting membrane potential in neurons and the role of the…Concept: This question tests your understanding of the resting membrane potential in neurons and the role of the sodium-potassium pump in maintaining ionic gradients.
Why (A) is correct:
1. Assertion (A) is true: The sodium-potassium pump (Na+/K+-ATPase) is crucial for maintaining the ionic gradients across the resting axonal membrane. It actively transports ions against their concentration gradients, contributing to the negative resting potential inside the neuron.
2. Reason (R) is false: The sodium-potassium pump transports 3 Na+ ions OUTWARD from the cell and 2 K+ ions INWARD into the cell for each ATP molecule hydrolyzed. The statement in Reason (R) incorrectly states that 3 Na+ are transported inwards and 2 K+ outwards.
Since Assertion (A) is true and Reason (R) is false, option A is the correct choice.
Why other options are wrong:
B) A is false but R is true: This is incorrect because A is true and R is false.
C) Both A and R are true and R is the correct explanation of A: This is incorrect because R is false.
D) Both A and R are true but R is NOT the correct explanation of A: This is incorrect because R is false.
Common Mistake: Students often confuse the direction of Na+ and K+ transport by the sodium-potassium pump. Remember Na+ goes out, K+ comes in.
NEET Tip / Mnemonic: Think of it as "Na-OUT, K-IN" and "3-2-1-ATP" (3 Na+ out, 2 K+ in, 1 ATP used).
Correct Answer: (A)
A is true but R is false.