Membrane Transport Proteins

Part A

What distinguishes facilitated diffusion from simple diffusion?

	No energy is used to move molecules across the membrane.
	Membrane proteins help move molecules across the membrane.
	Molecules move from a region of higher concentration to a region of lower concentration.
	Molecules move from a region of lower concentration to a region of higher concentration.

Correct

Membrane proteins facilitate the movement of molecules across the membrane.

Part B

Which of the following transporters does not use passive transport to move molecules across a membrane?

	Gramicidin ion channel
	GLUT-1 glucose transporter
	Valinomycin
	Sodium–potassium pump

Correct

This pump uses the energy provided by ATP hydrolysis to transport sodium and potassium ions across the membrane.

Part C

True or false? Active transport differs from passive transport in that active transport does not require an input of energy.

	True
	False

Correct

Active transport requires the input of energy, whereas passive transport is primarily driven by the gradient.Active transport requires energy, whereas passive transport does not.

Part D

Which membrane protein would be used to move glucose across a membrane from a region of higher concentration to a region of lower concentration?

	Pump
	Transporter
	No protein is necessary.
	Ion channel

Correct

The GLUT-1 transporter assists the diffusion of glucose through the membrane.

Part E

Which of the following statements is true about the net movement of an ion across a membrane by passive diffusion through a membrane channel?

	For every ion that diffuses through the membrane, a different ion diffuses in the opposite direction.
	The cell expends energy as the ion passes through the membrane.
	The charge on the other side of the membrane is generally the opposite of the ion's charge.
	There is a higher concentration of ions on the side of the membrane toward which the ion diffuses.

Correct

Ions tend to move toward regions of unlike charge.

Part F

True or false? During active transport through the sodium-potassium pump, ATP hydrolysis provides the energy to pump three sodium ions into the cell for every two potassium ions pumped out of the cell.

	True
	False

Correct

The sodium-potassium pump maintains a state in which the concentration of sodium is low inside the cell relative to the outside and the concentration of potassium is high inside the cell relative to the outside; thus, three sodium ions are pumped out of the cell and two potassium ions are pumped into the cell against the electrochemical gradient.

Part G

Lactose transport by membrane proteins occurs under conditions in which the concentration of lactose inside the cell is higher than the concentration outside the cell. What type of transport is used to move lactose into the cell?

	Facilitated diffusion
	Osmosis
	Simple diffusion
	Active transport

Correct

Under these conditions, lactose moves against its concentration gradient, so its transport will require energy.