What does it mean to move UP the concentration gradient?

Moving against the concentration gradient, or in simpler terms, moving from a low-concentration area to a high-concentration area.

Explanation:

This action uses energy, as according to entropy, the substance will move from a higher concentration to a lower concentration, and cells have to put extra energy to pump the molecules / substance up the concentration gradient.

It is mostly used to trigger chemical responses in cells, like in neuron synapses.

Hope this helped!

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