1) Overall, Na+ and glucose transport across epithelial cells __________. a) is
ID: 3474068 • Letter: 1
Question
1) Overall, Na+ and glucose transport across epithelial cells __________.
a) is down their concentration gradients
b) none of the above
c) requires energy
d) is by simple diffusion
2)Facilitated diffusion differs from simple diffusion in what way(s)?
a) The direction of transport is against the electrochemical gradient.
b) The rate of facilitated diffusion is dependent on the concentration gradient of the transported molecule.
c) The rate of facilitated diffusion depends on the number of carriers in the membrane.
d) Transport does not require energy.
3) Which of the following statements about epithelial transport is(are) true?
(a) The same types of transporters and channels are found in both the apical and basolateral membranes of epithelial cells.
(b) The Na+/K+ ATPase is found only in the basolateral membrane of epithelial cells.
All of these are correct.
(c) The movement of Na+ ions across the apical membrane of epithelial cells is dependent on the electrochemical gradient created by the Na+/K+ ATPase.
Answers b and c are correct
Explanation / Answer
1. b. none of the above (glucose transport is done against the gradient, and both sodium and glucose transport take place by the use of specialized transport proteins and channels, meaning the diffusion is not simple diffusion, but rather faciliated diffusion. No energy is used as the transporter is a symport)
2. c. The rate of facilitated diffusion depends on the number of carriers in the membrane. (as simple diffusion occurs through the membrane, but faciliated diffusion requires specialized transporters, the amount of which bottlenecks the rate of diffusion)
3. Na+/K+ ATPase is found in the basolateral membrane of the epithelial cell, as it pumps out the Na+ from the cell, so that more Na+ can be taken in from the intestinal lumen (apical membrane) along with glucose through the Na+/glucose symport. This is because the movement of Na+ outside the cell creates a negative gradient allowing the aforementioned import of glucose and Na+. Therefore, options b and c are correct.
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