Critical Thinking Questions

21. Why is it advantageous for the cell membrane to be fluid in nature?

22. Why do phospholipids tend to spontaneously orient themselves into something resembling a membrane?

23. How can a cell use an extracellular peripheral protein as the receptor to transmit a signal into the cell?

24. Discuss why the following affect the rate of diffusion: molecular size, temperature, solution density, and the distance that must be traveled.

25. Why does water move through a membrane?

26. Both of the regular intravenous solutions administered in medicine, normal saline and lactated Ringer’s solution, are isotonic. Why is this important?

27. Describe two ways that decreasing temperature would affect the rate of diffusion of molecules across a cell’s plasma membrane.

28. A cell develops a mutation in its potassium channels that prevents the ions from leaving the cell. If the cell’s aquaporins are still active, what will happen to the cell? Be sure to describe the tonicity and osmolarity of the cell.

29. Where does the cell get energy for active transport processes?

30. How does the sodium-potassium pump contribute to the net negative charge of the interior of the cell?

31. Glucose from digested food enters intestinal epithelial cells by active transport. Why would intestinal cells use active transport when most body cells use facilitated diffusion?

32. The sodium/calcium exchanger (NCX) transports sodium into and calcium out of cardiac muscle cells. Describe why this transporter is classified as secondary active transport.

33. Why is it important that there are different types of proteins in plasma membranes for the transport of materials into and out of a cell?

34. Why do ions have a difficult time getting through plasma membranes despite their small size?