Describe the function of carriers proteins.
Ion is carried down its concentration gradient, it does not require energy.
Ion is carried up its concentration gradient, it does require energy.
Many molecules that cannot cross the cell membrane are "ferried"
This can occur up or down a concentration dradient (high to low, low to high)
If it occurs against a concentration gradient, energy is required.... Energy comes from ATP, other molecules that run down their concentration gradient.