Question abot concentration gradient

[jojo4335]

How can substances move across a membrane against a concentration gradient? What are the processes that can accomplish this movement? Give an example of when this might need to take place.

[GreenDog]

First of all I have a hunch that the answer is in your coursebook/notebook so these might be good places to start looking for an answer.
But anyway I will remind you those molecules in the cell have a charge. The cell membrane is also charged, negatively. It means that positive molecules are driven into the cell and negative out of the cell…
Another way to move molecules out of the cell is using a transporter which uses ATP…

[jojo4335]

I have read my text and for some reason the whole thing is very confusing

[GreenDog]

Are you studying Biochemistry, Physiology or trying to understand it in general?

According to the second law of thermodynamics every system in nature wants to reach equilibrium, however in biology only dead systems are in equilibrium. To create a system which is nit in equilibrium we need energy which is provided by ATP. Using ATP the cell creates a gradient of concentrations – meaning the concentration of some molecules is larger in the cell and of some out of the cell. The other gradient is of (electric) potentials. The inner side of the cell is negatively charged (compared to the outer). It means that there are two forces which affect a certain molecule. The chemical gradient might be pulling her in and the potential difference out, or the other way around, or both working in the same direction.
So, to move a molecule across the membrane against the chemical gradient maybe all you need is to open the right channel and it will move because of the electric force is stronger, as happens in synaptic transmission.
And another way might be to use a transporter to give you energy either something that uses ATP directly to pull something against its driving force, or a coupled transporter which moves one substance according to the driving force and uses the energy to move something else against the driving force.

[nikeman]

How can substances move across a membrane against a concentration gradient? What are the processes that can accomplish this movement? Give an example of when this might need to take place.

all i can tell you is Active Transport proteins