inherently unstable ion concentration gradients are essential for many physiological functions so a nonuniform ion distribution, termed an ion concentration gradient, exists between the cell’s interior and its exterior, despite the Second Law, and that gradient is maintained over time. How can that be? In order to maintain inherently unstable concentration gradients over time the cell has to operate ion pumps, pumping ions against the gradient—just like the bird flapping its wings to stay aloft. Of course, in order to operate those ion pumps, the cell must utilize energy, and that energy has
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