Unit 2: Cell Membrane and Permeability - Practice Quiz

1 Which type of molecule forms the main structural layer of most cell membranes?

2 Which part of a phospholipid is attracted to water?

3 Which part of a phospholipid avoids water?

4 Which molecule helps regulate the fluidity of animal cell membranes?

5 What is the basic arrangement of phospholipids in a cell membrane?

6 Why is the cell membrane described as fluid?

7 What does the term "mosaic" refer to in the fluid mosaic model?

8 Which membrane component is often found attached to the outside surface of proteins or lipids?

9 What generally happens to membrane fluidity when temperature increases?

10 Which type of fatty acid usually increases membrane fluidity?

11 What effect do saturated fatty acid tails usually have on membrane fluidity?

12 What is the main effect of cold temperatures on a membrane?

13 Which membrane protein helps substances cross the membrane?

14 What is one function of receptor proteins in a cell membrane?

15 Which membrane protein can act as an enzyme?

16 What is passive transport?

17 In which direction do substances usually move during diffusion?

18 What is required for active transport?

19 What is endocytosis?

20 What is exocytosis?

21 A membrane is exposed to a chemical that removes cholesterol while leaving phospholipids intact. Which change is most likely at moderate temperatures?

22 Why do phospholipids spontaneously form bilayers in an aqueous environment?

23 A membrane carbohydrate is attached directly to a lipid rather than to a protein. What structure has been formed?

24 A researcher labels proteins on the outer surface of a cell and observes that many labels move laterally after several minutes. Which model best explains this observation?

25 A membrane protein is exposed to the cytoplasm on one side and the extracellular fluid on the other. Which property of the membrane does this demonstrate?

26 A drug binds to membrane proteins but does not dissolve the phospholipid bilayer. Which membrane feature allows the drug to affect selected cell functions?

27 Two membranes contain the same number of phospholipids. Membrane X has more unsaturated fatty acid tails than membrane Y. At low temperature, which membrane should remain more fluid?

28 A cell adapted to a colder environment increases the proportion of unsaturated phospholipids in its membrane. What is the main benefit?

29 If membrane temperature rises substantially, which change is most likely to occur without another stabilizing factor?

30 A cell accumulates a molecule inside using a membrane protein that changes shape after binding the molecule. Which function is being performed?

31 A membrane protein binds a signaling molecule outside the cell and triggers a response inside the cell without transporting the molecule across. What is its primary function?

32 A protein is attached to the inner surface of the plasma membrane but does not extend through the lipid bilayer. Which type of membrane protein is it?

33 A molecule moves from an area of lower concentration to an area of higher concentration through a membrane protein. Which process is most likely involved?

34 A molecule crosses a membrane through a channel protein from high concentration to low concentration without ATP use. Which process describes this movement?

35 A cell uses ATP to move sodium ions out of the cytoplasm even though sodium concentration is already higher outside. What does this process illustrate?

36 A red blood cell is placed in a solution with a lower solute concentration than its cytoplasm. What is the most likely result?

37 A membrane is permeable to water but not to a dissolved solute. Which condition would cause water to move into a cell?

38 A secretory cell releases a protein outside the cell when a vesicle fuses with the plasma membrane. Which process is occurring?

39 A cell surrounds and internalizes a large bacterium using extensions of its plasma membrane. Which type of endocytosis is this?

40 A cell selectively takes in a hormone after it binds to a specific receptor concentrated in a coated membrane region. Which process is most likely involved?

41 A membrane lipid has two fatty-acid tails: one saturated 18-carbon tail and one cis-unsaturated 18-carbon tail. Compared with a lipid containing two saturated 18-carbon tails, what is the most likely consequence at the same temperature?

42 A membrane is experimentally made more permeable to small nonpolar molecules without changing its protein content. Which alteration most directly explains this result?

43 Why does cholesterol reduce membrane permeability to small polar molecules while helping prevent phospholipid packing at low temperatures?

44 A researcher treats intact red blood cells with a reagent that removes exposed carbohydrate groups but leaves proteins and lipids intact. Which function is most directly impaired?

45 A fluorescent membrane protein is bleached in a small region. Fluorescence returns only when the protein is experimentally cleaved from its cytoskeletal attachment. What does this result demonstrate?

46 A membrane protein is inserted into the endoplasmic reticulum with its large domain facing the ER lumen. After vesicular trafficking to the plasma membrane, where will that domain be located?

47 A membrane protein contains several hydrophobic segments, each approximately 20 amino acids long. Which conclusion is most strongly supported?

48 A lipid-bound fluorescent marker remains confined to one leaflet after extensive lateral diffusion but does not appear in the opposite leaflet. Which process is most limited under these conditions?

49 A microorganism increases the proportion of short, cis-unsaturated fatty acids after a sudden temperature decrease. What is the primary adaptive benefit?

50 Two liposomes have identical lipid compositions, but one contains phospholipids with 16-carbon tails and the other with 20-carbon tails. At a temperature just above both transition temperatures, which liposome generally has greater fluidity?

51 A membrane's temperature rises substantially, but its fluidity changes very little. Which compositional response would best explain this observation?

52 A membrane receptor binds an extracellular ligand but has no cytosolic catalytic domain. Its cytosolic tail associates with a protein kinase. Which function does this arrangement most directly support?

53 A cell loses a membrane protein that binds extracellular matrix fibers and also connects internally to actin. Which cellular property is most directly affected?

54 A mutation changes a channel protein's selectivity filter but leaves its gating mechanism intact. Which outcome is most likely?

55 An ion has a concentration gradient favoring movement into a cell but an electrical gradient opposing entry. Under what condition will the ion still enter spontaneously?

56 A drug blocks the sodium-potassium pump in an animal cell. Initially, which transport process is most directly impaired before secondary effects become prominent?

57 A symporter moves glucose into an epithelial cell using the inward sodium gradient, even though glucose concentration is already higher inside. Which statement is correct?

58 A membrane is permeable to water but not to a large intracellular solute. The intracellular solute concentration increases while extracellular solute concentration remains constant. What is the immediate tendency?

59 A neuron releases neurotransmitter when calcium enters its presynaptic terminal. Which event most directly follows the calcium signal?

60 A cell internalizes a receptor-ligand complex in clathrin-coated vesicles. The ligand is later degraded, while the receptor returns to the plasma membrane. Which process explains receptor recovery?