Movement of Na+ ions into a nerve cell during the upstroke of an action potential is an example of of the following transport mechanismSelect one:a. Primary active transportb. Simple diffusionc. Co-transportd. Facilitated diffusione. Counter-transport
Question
Movement of Na+ ions into a nerve cell during the upstroke of an action potential is an example of of the following transport mechanismSelect one:a. Primary active transportb. Simple diffusionc. Co-transportd. Facilitated diffusione. Counter-transport
Solution
The movement of Na+ ions into a nerve cell during the upstroke of an action potential is an example of "d. Facilitated diffusion".
Here's why:
Facilitated diffusion is a type of passive transport that allows substances to cross membranes with the assistance of special transport proteins. Some molecules and ions such as Na+ ions are unable to pass through the phospholipid bilayer of cell membranes. With the help of carrier proteins or ion channels, these molecules can still diffuse across the membrane, down their concentration gradient.
During an action potential, voltage-gated Na+ channels open in response to a change in membrane potential. This allows Na+ ions to flow into the neuron, down their electrochemical gradient, causing the membrane to depolarize. This is the upstroke of the action potential. This process does not require energy, which is why it is not a form of active transport (option a). It is also not simple diffusion (option b) because it requires the assistance of a protein. It is not co-transport or counter-transport (options c and e) because only one type of ion is moving, and it is not moving in conjunction with another ion or molecule.
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