B 2.1 membrane and membrane transport

1. What is the plasma membrane made of?

Phospholipid bilayer.

2. What are the two parts of a phospholipid?

Hydrophilic phosphate head + hydrophobic hydrocarbon tails.

3. Why is the membrane selectively permeable?

Hydrophobic interior blocks polar/large molecules.

4. Which molecules cross easily?

Nonpolar, hydrophobic molecules (e.g., O₂).

5. Which molecules cross poorly?

Glucose, ions, large polar molecules.

6. What is simple diffusion?

Passive movement from high → low concentration.

7. Does simple diffusion require energy?

No

8. Which molecules use simple diffusion?

Small, nonpolar molecules.

9. Why can’t glucose or ions diffuse simply?

Membrane has low permeability to hydrophilic molecules.

They require specific transport mechanisms to cross.

10. What are integral proteins?

Embedded in membrane; often transmembrane.

11. What are peripheral proteins?

Attached to membrane surface or integral proteins.

12. Which proteins span the entire bilayer?

Integral transmembrane proteins.

13. What is osmosis?

Passive movement of water from low solute → high solute concentration.

14. Why does water move toward higher solute concentration?

Solutes bind water → fewer free water molecules.

15. What increases water permeability?

Aquaporins.

16. Does osmosis require energy?

No

17. What molecules use facilitated diffusion?

Ions, glucose, polar molecules.

18. What proteins are used?

Channel proteins.

19. Is facilitated diffusion selective?

Yes — channels are specific.

20. Does it require energy?

No — moves down gradient.

21. Can channels open/close?

Yes — regulates permeability.

22. What is active transport?

Movement against gradient; requires ATP.

23. What proteins perform active transport?

Pump proteins.

24. Example of active transport?

Sodium‑potassium pump (3 Na⁺ out, 2 K⁺ in).

25. Which transport types are selective?

Facilitated diffusion, active transport.

26. Which are non‑selective?

Simple diffusion, osmosis.

27. What are glycoproteins?

Proteins with carbohydrate chains.

They play roles in cell signaling and recognition.

28. What are glycolipids?

Lipids with carbohydrate chains.

29. What is their function?

Cell recognition (self vs non‑self).

30. What is the glycocalyx?

Carbohydrate‑rich outer layer aiding adhesion and tissue stability.

31. What does the fluid mosaic model describe?

Phospholipid bilayer with mobile proteins, glycoproteins, glycolipids.

32. Why is the membrane fluid?

Components move laterally.

33. How do saturated fatty acids affect fluidity?

Decrease fluidity (tight packing).

34. How do unsaturated fatty acids affect fluidity?

Increase fluidity (kinked chains).

35. How do organisms adapt to temperature?

Adjust ratio of saturated/unsaturated fatty acids.

36. Example of adaptation?

Antarctic fish → more unsaturated fatty acids.

37. Where is cholesterol located?

Embedded in bilayer interior.

38. How does cholesterol affect fluidity?

Buffers fluidity — stabilizes at high temps, prevents solidification at low temps.

39. What percentage of membrane lipids is cholesterol?

20–40%.

40. What is endocytosis?

Membrane invagination → vesicle formation → substances enter cell.

41. What is exocytosis?

Vesicles fuse with membrane → release contents outside cell.

42. Do these processes (endocytosis + exocytosis) require energy?

yes

43. What are voltage‑gated channels?

Open/close based on membrane voltage.

44. What are neurotransmitter‑gated channels?

Open when neurotransmitter binds.

45. Example of neurotransmitter‑gated channel?

Nicotinic acetylcholine receptor.

46. What do exchange transporters do?

Move ions in opposite directions.

47. What pump maintains membrane potential?

Na⁺/K⁺ pump.

48. What is indirect active transport?

Uses gradient of one molecule to drive transport of another.

49. Example of indirect active transport?

Sodium‑glucose cotransporter.

50. Where is sodium‑glucose cotransport used?

Kidney (glucose reabsorption), small intestine (glucose absorption).

51. What do CAMs do?

Hold cells together in tissues.

52. Where are CAMs located?

Embedded in membrane.

53. What do CAMs form?

Junctions between cells.

They facilitate cell adhesion and communication.