Which of the following forms of membrane transport require specific membrane proteins?a. diffusion;b. exocytosis;c. facilitated diffusion;d. active transport;e. facilitated diffusion and active transport

Which of the following statements about cotransport of solutes across a membrane is correct?

Consider the transport of protons and sucrose into a plant cell by the sucrose-proton cotransport protein. Plant cells continuously produce a proton gradient by using the energy of ATP hydrolysis to pump protons out of the cell. Why, in the absence of sucrose, do protons not move back into the cell through the sucrose-proton cotransport protein?

Which of the following correctly describes a general property of all electrogenic pumps?

Suppose a cell is placed in a solution with a high concentration of potassium and no sodium. How would the cellular sodium–potassium pump function in this environment?a. It would stop moving ions across the membrane.b. It would continue using ATP to pump sodium out of the cell and potassium into the cell.c. It would move sodium and potassium ions across the membrane, but no ATP would be used.d. It would reverse the direction of sodium and potassium ions to move them against their gradients.

Which of the following cannot pass through the membrane without the help of a membrane protein?a. carbon dioxide;b. water;c. oxygen;d. charged molecules