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Question

Read the following statement (a-d)
(a) Neurons are excitable cells because their membranes are in a polarised state.
(b) Ion channels are completely permeable of different ions.
(c) Axolemma is less permeable to K+ ions in resting stage.
(d) Axolemma is impermeable to negatively charged proteins in axoplasm.
How many of above statement are wrong?

A
one
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B
two
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C
three
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D
four
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Solution

The correct option is B two
Different types of ion channels are present on the nerve membrane. These ion channels are selectively permeable to different ions. Therefore, neurons are excitable cells because their membranes are in a polarised state. Ion channels are not completely permeable of different ions as the channel pore is just one or two atoms wide at its narrowest point and is selective for specific species of ion, such as sodium or potassium. When a neuron is resting (not conducting any impulse) the axonal membrane (axolemma) is comparatively more permeable to potassium ions (K+) and nearly impermeable to sodium ions (Na+). Similarly, the membrane is impermeable to negatively charged proteins present in the axoplasm.
So, the correct answer is 'two'.

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