Plasma Membrane - AP Biology

1. Which molecules can easily pass through the plasma membrane?

   Small nonpolar molecules. They dissolve in the lipid bilayer and cross without assistance.

2. Identify a function of glycoproteins in the plasma membrane.

   Cell recognition and signaling. Sugar chains on proteins enable cell identification and communication.

3. Which type of molecules diffuse most easily through the phospholipid bilayer?

   Small nonpolar molecules such as $O_2$ and $CO_2$. No charge and small size allow easy passage through lipids.

4. What is a concentration gradient?

   A difference in solute concentration across space or a membrane. Creates driving force for passive transport processes.

5. Identify the transport type: $Na^+$ moves against its gradient using ATP hydrolysis.

   Primary active transport. ATP directly powers uphill ion movement.

6. Identify the transport type: a ligand binds a receptor and the membrane forms a coated vesicle.

   Receptor-mediated endocytosis. Specific binding triggers clathrin-coated vesicle formation.

7. What is the plasma membrane in cells, in terms of its basic structure and location?

   A selectively permeable phospholipid bilayer surrounding the cell. Forms the boundary that controls cellular entry and exit.

8. What is the term for the cell's release of materials to the extracellular space?

   Exocytosis. Active transport process moving materials from inside cell outward.

9. What is secondary active transport (cotransport)?

   Uses energy stored in an ion gradient to move another solute uphill. One gradient powers movement against another gradient.

10. What role do proteins play in the plasma membrane?

    Facilitate transport and signal transduction. Act as channels, carriers, and receptors for membrane functions.

11. What is the main function of the plasma membrane in maintaining homeostasis?

    Regulates movement of substances into and out of the cell. Controls what enters/exits to maintain internal balance.

12. What is an aquaporin?

    A channel protein that facilitates rapid water transport. Specialized channels greatly increase water permeability.

13. What makes the phospholipid bilayer amphipathic?

    Hydrophilic phosphate heads and hydrophobic fatty acid tails. Has both water-loving and water-fearing parts.

14. Identify the main structural component of the plasma membrane.

    Phospholipid bilayer. Forms the fundamental structure with hydrophilic heads and hydrophobic tails.

15. Which part of a phospholipid faces the cytosol and extracellular fluid in a bilayer?

    Hydrophilic phosphate heads. Water-loving heads interact with aqueous environments.

16. What is a gated ion channel?

    A channel that opens or closes in response to a stimulus. Stimulus controls channel opening for regulated transport.

17. What property of the plasma membrane is described as 'selectively permeable'?

    Allows certain substances to pass while blocking others. Permeability depends on size, charge, and polarity of substances.

18. What does the term 'amphipathic' refer to regarding phospholipids?

    Having both hydrophilic and hydrophobic regions. Dual nature with water-loving and water-avoiding molecular regions.

19. Which change increases membrane fluidity at low temperatures: more unsaturated tails or more saturated tails?

    More unsaturated fatty acid tails. Double bonds create kinks that increase fluidity.

20. Identify the tonicity: a cell placed in a solution with higher solute concentration outside.

    Hypertonic to the cell. Higher external solute concentration draws water out.

21. Which molecules have the greatest difficulty crossing the bilayer without proteins?

    Ions and large polar molecules. Charge and size make passage through lipid core difficult.

22. What is endocytosis?

    The cell takes in material by forming vesicles from the membrane. Membrane invagination brings materials into the cell.

23. What is the primary role of cholesterol in animal cell membranes?

    Buffers membrane fluidity and decreases permeability to small solutes. Modulates membrane properties without forming barriers.

24. How do membrane proteins assist in facilitated diffusion?

    By providing pathways for specific molecules. Create specific channels for molecules that cannot cross lipid bilayer.

25. What is pinocytosis?

    A type of endocytosis for fluid uptake. Cell drinking process that engulfs liquid and dissolved substances.

26. Which term describes the membrane's ability to move and flow?

    Fluidity. Physical property allowing membrane components to move laterally.

27. Which transport type requires ATP directly: primary active transport or secondary active transport?

    Primary active transport. Direct ATP hydrolysis powers the transport process.

28. What is the sodium-potassium pump, in terms of ions moved per ATP?

    Moves $3 \, Na^+$ out and $2 \, K^+$ in per ATP hydrolyzed. Creates electrical gradient by unequal ion exchange.

29. Identify the type of transport that uses vesicles to move large particles.

    Endocytosis and exocytosis. Bulk transport processes for materials too large for channels.

30. What is the glycocalyx?

    Carbohydrate-rich cell surface layer for recognition and adhesion. Carbohydrate layer enables cell-cell interactions.

31. What is electrochemical gradient in membrane transport?

    Combined effect of concentration gradient and electrical charge difference. Both chemical and electrical forces affect ion movement.

32. Identify the term for the movement of solutes down their concentration gradient.

    Diffusion. Passive movement from high to low concentration areas.

33. What is phagocytosis?

    A type of endocytosis for large particle uptake. Cell eating process where membrane engulfs solid particles.

34. What is the role of peripheral proteins in the plasma membrane?

    To provide support and act as enzymes. Attached to membrane surface, not embedded within bilayer.

35. What is active transport across the plasma membrane?

    Movement against a gradient requiring energy, usually from ATP. Energy input overcomes unfavorable concentration gradients.

36. Which structure assists with cell-cell communication in the plasma membrane?

    Glycolipids and glycoproteins. Carbohydrate chains on membrane lipids and proteins enable recognition.

37. What is the function of glycoproteins in cell recognition?

    To act as markers for cellular identification. Surface carbohydrates serve as cellular identification tags.

38. What is the direction of water movement during osmosis relative to solute concentration?

    From lower solute concentration to higher solute concentration. Water moves to dilute higher solute concentrations.

39. Identify the immediate water movement: a cell in a hypertonic solution relative to its cytosol.

    Water moves out of the cell. Water follows osmotic gradient toward higher solutes.

40. What is facilitated diffusion across the plasma membrane?

    Passive transport down a gradient via channel or carrier proteins. Requires protein help but no energy for downhill movement.

41. Which process describes the movement of water across the plasma membrane?

    Osmosis. Water diffuses across the membrane down its concentration gradient.

42. What is the role of ATP in active transport across the plasma membrane?

    To provide energy for moving substances against the gradient. Cellular energy currency powers transport against concentration gradients.

43. What is phagocytosis?

    Endocytosis of large particles, forming a food vacuole. Cell eating process for large particle ingestion.

44. Identify the transport type: glucose moves down its gradient via a carrier protein.

    Facilitated diffusion. Downhill movement with protein assistance requires no energy.

45. Which type of protein spans the entire plasma membrane?

    Integral proteins. These transmembrane proteins extend across the entire bilayer.

46. What is a membrane carrier protein?

    A protein that binds a solute and changes shape to move it across. Conformational changes facilitate transport across membrane.

47. What is the function of cholesterol in the plasma membrane?

    To maintain membrane fluidity. Prevents membrane from becoming too rigid or too fluid.

48. Which process involves the fusion of vesicles with the plasma membrane?

    Exocytosis. Vesicles merge with membrane to release cellular contents outside.

49. What is the primary role of the plasma membrane in cell signaling?

    To receive and transmit signals via receptor proteins. Membrane proteins detect signals and initiate cellular responses.

50. What is the role of aquaporins in the plasma membrane?

    Facilitate water transport. Specialized protein channels that allow rapid water movement.

51. What is pinocytosis?

    Nonselective endocytosis of extracellular fluid and dissolved solutes. Cell drinking process takes in surrounding fluid.

52. What is a glycoprotein in the plasma membrane?

    A membrane protein with covalently attached carbohydrate chains. Sugar coating provides cell identity and recognition.

53. Which part of the phospholipid is hydrophilic?

    The phosphate head. The phosphate group is polar and attracted to water.

54. Which change decreases membrane fluidity at moderate temperatures: longer tails or shorter tails?

    Longer fatty acid tails. More tail interactions reduce molecular movement.

55. What is diffusion across a membrane?

    Net movement down a concentration gradient. Movement from high to low concentration without energy input.

56. Which component of the plasma membrane acts as a barrier to polar molecules?

    The hydrophobic core of the phospholipid bilayer. Fatty acid tails repel charged and polar molecules.

57. What is osmosis in terms of membrane transport?

    Diffusion of water across a selectively permeable membrane. Water follows concentration gradients like other molecules.

58. What is the function of carrier proteins in the plasma membrane?

    To transport specific substances across the membrane. Bind and facilitate movement of specific molecules across membrane.

59. What is simple diffusion across the plasma membrane?

    Diffusion directly through the lipid bilayer without transport proteins. No protein assistance needed for this passive process.

60. What is the primary function of the lipid bilayer in the plasma membrane?

    To provide a barrier to water-soluble substances. Hydrophobic interior blocks passage of polar and charged substances.

61. What is receptor-mediated endocytosis?

    Specific uptake via ligand binding to membrane receptors. Selectivity achieved through specific receptor binding.

62. What is the fluid mosaic model describing about the plasma membrane?

    A fluid lipid bilayer with a mosaic of embedded, mobile proteins. Describes membrane as dynamic with movable protein components.

63. Which plasma membrane component acts as a signal receptor?

    Receptor proteins. Membrane proteins that detect and bind specific signaling molecules.

64. Identify the term for diffusion of water through a selectively permeable membrane.

    Osmosis. Specific case of diffusion involving only water molecules.

65. Which molecule stabilizes the plasma membrane by adjusting fluidity?

    Cholesterol. Modulates membrane flexibility by filling spaces between phospholipids.

66. What is selective permeability in the context of the plasma membrane?

    The membrane allows some substances to cross more easily than others. Membrane acts as a selective barrier, not freely permeable.

67. What is a membrane channel protein?

    A protein forming a hydrophilic passageway for specific solutes. Provides selective pathway through membrane barrier.

68. What is membrane potential?

    Voltage difference across a membrane due to unequal ion distribution. Electrical charge separation creates cellular voltage.

69. What is exocytosis?

    Vesicles fuse with the membrane to release contents outside the cell. Membrane fusion allows bulk transport out of cell.

70. What is the primary function of the plasma membrane?

    To regulate the movement of substances in and out of the cell. Acts as a selective barrier controlling what enters and exits the cell.

71. What does the 'fluid mosaic model' describe?

    The dynamic and flexible nature of the plasma membrane. Describes membrane as flowing structure with embedded proteins.

72. Identify the type of passive transport involving carrier proteins.

    Facilitated diffusion. Passive transport using proteins to move specific molecules down gradients.

73. What is the function of receptor proteins in the plasma membrane?

    To bind signaling molecules and initiate cellular responses. Enable cells to detect and respond to chemical signals.

74. What distinguishes passive transport from active transport?

    Passive transport does not require energy, active transport does. Energy requirement distinguishes these two transport mechanisms.

75. Identify the term for the uptake of large particles by a cell.

    Phagocytosis. Active process where cells engulf and internalize large particles.

76. Which molecule primarily composes the hydrophobic core of the membrane?

    Fatty acid tails of phospholipids. Hydrophobic chains form the water-repelling interior of membrane.

77. Which lipid component is essential for membrane fluidity and stability?

    Cholesterol. Steroid molecule that regulates membrane physical properties.

78. What is the term for the movement of ions against their concentration gradient?

    Active transport. Requires energy to move substances from low to high concentration.

79. Which part of a phospholipid forms the interior core of the bilayer?

    Hydrophobic fatty acid tails. Water-fearing tails cluster away from water.

80. Which cellular process involves the uptake of molecules via vesicles?

    Endocytosis. Membrane invaginates to bring external material into the cell.

Study these flashcards