Chapter 6 Study Questions

What does Nernst equation describe? If the current carried by K⁺ ions diffusing through a K⁺ channel is plotted against the membrane potential, at what potential will the direction of current reverse?

Textbook Reference: Transport of Ions across Membrane Barriers, pp. 147–148; Membrane Transport Processes, p. 152
What is meant by the term “active transport”? What is the difference between primary and secondary active transport?

Textbook Reference: Transport of Ions across Membrane Barriers, pp. 147–148; Membrane Transport Processes, pp. 151–154
Membrane channels and carriers both show changes in protein conformation. What is the role of such conformation changes in: (1) channels, and (2) carriers?

Textbook Reference: Membrane Transport Processes, pp. 150–154
How can the operation of the plasma membrane H⁺-ATPase affect: (1) the diffusion of K⁺ through membrane channels, and (2) the accumulation of sugars from the apoplast into the cell?

Textbook Reference: Membrane Transport Processes, pp. 151–154
Detection of external signals by plant cells often results in a transient rise in the concentration of Ca²⁺ ions in the cytoplasm. What transport processes can cause such an increase in cytoplasmic Ca²⁺, and what transport processes can remove the excess Ca²⁺ and restore the level of Ca²⁺ to its resting state?

Textbook Reference: Membrane Transport Proteins, pp. 158–159
In the transport of an ion from the soil solution to the xylem, what is the minimum number of times it must cross a cell membrane? What transport mechanisms are likely to be involved at each membrane?

Textbook Reference: Ion Transport in Roots, pp. 163–165