Describe the chemical and electrical driving forces that move ions across a memb

Question

Describe the chemical and electrical driving forces that move ions across a membrane.

Describe the process whereby the Na+/K+ pump is involved in moving those ions across a membrane.
Describe the factors that affect the rate of passive transport of molecules across a membrane.

Since it is the electrochemical gradient that determines the direction and magnitude of an ion's movement across a membrane, describe how one can determine the direction of ion movement based on the electrical and chemical gradients.

Explanation / Answer

The electrical and chemical gradients of a membrane tend to drive sodium into and potassium out of the cell, and active transport works against these gradients.

To move substances against a concentration or electrochemical gradient, the cell must utilize energy in the form of ATP during active transport. membrane.

Primary active transport, which is directly dependent on ATP, moves ions across a membrane and creates a difference in charge across that membrane.

Secondary active transport, created by primary active transport, is the transport of a solute in the direction of its electrochemical gradient and does not directly require ATP.

Carrier proteins such as uniporters, symporters and antiporters perform primary active transport and facilate the movement of solutes across the cell's membrane.

The interior of living cells is electrically negative with respect to the extracellular fluid in which they are bathed. At the same time, cells have higher concentrations of potassium (K+) and lower concentrations of sodium ( Na+) than does the extracellular fluid. In a living cell, the concentration gradient of Na+ tends to drive it into the cell, and the electrical gradient of Na+ ( a positive ion) also tends to drive it inward to the negatively charged interior. The situation is more complex, however, for other elements such as potassium. The electrical gradient of K+, a positive ion, also tends to drive it into the cell, but the concentration gradient.

In order to move against the concentration gradient ( from low to high concentration), particles must undergo active transport. During active transport, molecules are transported across the membrane via carrier proteins. This form of transportation requires the use of energy in the form of ATP (adenine triphosphate).

Size is another factor that affects the movement of molecules across a semipermeable membrane. Sometimes molecules are moving down the concentration gradient but are too large to fit through the spaces between the lipid bilayer. These molecules undergo what is called facilitated diffusion. During facilitated diffusion, a carrier protein is used but energy is not.

Charged particles also cannot diffuse across by themselves and also require a carrier.

An electrochemical gradient is a gradient of an electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts, the chemical gradient, or difference in solute concentration across a membrane, and the electrical gradient, or difference in charge across a membrane. When there are unequal concentrations of an ion across a permeable membrane, the ion will move across the membrane from the area of higher concentration to the area of lower concentration through simple diffusion. Ions also carry an electric charge that forms an electric potential generates a force that drives ion diffusion until the charges are balanced on both sides of the membrane.

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