Membrane Transport & Cell signaling

What is a concentration gradient?

A difference in the concentration of a substance between two areas.

Which direction does a substance naturally move down its concentration

From higher concentration → lower concentration.

What is an osmotic gradient?

A difference in solute concentration that causes water to move across a selectively permeable membrane

What is a pressure gradient?

A difference in physical pressure that drives fluid movement from higher pressure toward lower pressure

What is an electrical gradient?

A difference in electrical charge that influences the movement of ions.

What are the four gradients you need to recognize?

Concentration, osmotic, pressure, and electrical.

What two gradients determine the movement of an ion?

Its chemical/concentration gradient and its electrical gradient.

What is diffusion?

The net movement of particles from an area of higher concentration to lower concentration.

9. Q: What happens to diffusion rate when the concentration gradient increases?

Diffusion increases.

What happens when membrane surface area increases?

Diffusion increases.

11What happens when molecular size increases?

Diffusion generally decreases.

What happens when lipid solubility increases?

Diffusion through the lipid membrane generally increases.

What four factors should you remember for diffusion?

Concentration gradient, surface area, solubility, and molecular size.

What is passive transport?

Movement across a membrane that does not require cellular energy/ATP.

Does passive transport move substances with or against their gradient?

Down their gradient.

What is active transport?

Movement across a membrane that requires energy, directly or indirectly, to move substances against a gradient

Does facilitated diffusion require ATP?

No. It is passive.

Does active transport require membrane proteins?

Yes. Active transport uses pumps or transport proteins.

What is the easiest way to remember passive vs. active?

Passive = downhill. Active = uphill.

What is simple diffusion?

A: Movement directly through the lipid bilayer from high → low concentration.

Does simple diffusion require a transport protein?

No

Give examples of substances that can cross by simple diffusion.

Small lipid-soluble molecules such as O₂ and CO₂.

What is facilitated diffusion?

Passive movement down a gradient through a membrane protein.

Does facilitated diffusion require ATP?

No

What is osmosis?

The movement of water across a selectively permeable membrane.

What is primary active transport?

Active transport that uses ATP directly.

Give an example of primary active transport.

The sodium-potassium pump (Na⁺/K⁺ ATPase).

What is secondary active transport?

Transport that uses energy stored in an ion’s electrochemical gradient rather than directly using ATP at the transporter