2.1.2 Cell membrane structure and the fluid mosaic model Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 2

The 20 questions

1. Which molecules form the basic framework of the cell membrane according to the fluid mosaic model?

   • A phospholipid bilayer with hydrophilic heads facing outwards and hydrophobic tails facing inwards
   • A single layer of glycogen molecules that are cross-linked by peptide bonds
   • A double layer of proteins with hydrophobic regions facing the cytoplasm and the outside
   • A bilayer of cellulose fibres that are arranged parallel to the surface of the cell

2. Why are the tails of phospholipids hydrophobic?

   • They are long non-polar hydrocarbon chains that do not form hydrogen bonds with water
   • They contain charged phosphate groups that repel water molecules strongly
   • They contain glycosidic bonds that are broken by water, which prevents them dissolving
   • They are made of amino acids that are insoluble in water at body temperature

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

   • It forms the main channels through which water passes by osmosis across the membrane
   • It is an enzyme that catalyses the breakdown of phospholipids in the membrane
   • It forms the cell wall that gives the membrane its rigidity in plants
   • It helps to regulate membrane fluidity, making the membrane less fluid at high temperatures

4. Which feature of the fluid mosaic model explains why proteins can move within the membrane?

   • The membrane contains no water, so the proteins are solid and cannot move at all
   • The phospholipids are free to move laterally, so the bilayer behaves as a fluid
   • The phospholipids are covalently bonded to each other, so the membrane is rigid and immobile
   • The proteins are fixed to the cytoskeleton, which stops any movement within the membrane

5. What is the function of channel proteins in membrane transport?

   • They break down large molecules into smaller units before they cross the membrane by diffusion
   • They provide a water-filled pore through which specific ions or small polar molecules can diffuse
   • They bind to large molecules and change shape to carry them across the membrane against a gradient
   • They form the hydrophobic core of the membrane, which prevents any substance from crossing

6. Which description best matches carrier proteins in membrane transport?

   • They bind a specific molecule and change shape to move it across the membrane
   • They are attached to the outside of the cell and digest molecules before they can enter
   • They are made of cellulose and form a rigid wall that prevents molecules from passing
   • They form open pores that let any molecule of any size pass through the membrane freely

7. Which of these is a glycoprotein's role in the cell membrane?

   • It acts as the main source of ATP for the cell during periods of anaerobic respiration
   • It forms the hydrophobic tails of the bilayer, which keep the membrane impermeable
   • It acts as a cell-surface marker for recognition by other cells and by the immune system
   • It breaks down hydrogen peroxide inside the cell to protect the membrane from damage

8. Why do the membrane lipids and proteins described by the fluid mosaic model form a mosaic?

   • The membrane is made of identical protein units joined end to end in a regular repeating pattern
   • The lipid bilayer is a single sheet of glycogen that is cut into separate pieces by proteins
   • The phospholipids are arranged in rows that alternate with rows of carbohydrate chains
   • Proteins are scattered within and across the lipid bilayer in a pattern that looks like a mosaic

9. What evidence led to the modification of earlier models of the membrane to the fluid mosaic model?

   • Experimental data showing that membrane proteins can move laterally and that the membrane is fluid
   • Observations that the membrane is a rigid wall of cellulose in all animal cells
   • Evidence that the membrane contains no lipids, so it must be made entirely of protein
   • Measurements showing that membranes are made of glucose units joined by glycosidic bonds

10. Why do scientists describe the fluid mosaic model as an interpretation of data rather than a fixed truth?

    • It was proven by a single experiment, and so it can never be changed by any later discovery
    • It is a rule from the law of diffusion, which is a fixed truth with no room for revision
    • It is an explanation that fits current data, and it can be revised as new evidence emerges
    • It is a theory that has no basis in experimental data, which is why it is open to revision

11. A student investigates the effect of temperature on the permeability of beetroot cell membranes by measuring the colour of the solution. What does a darker solution indicate?

    • The membrane has become more rigid, so pigment cannot leave the cell
    • The temperature has no effect on the colour, so the membrane is unchanged
    • More pigment has leaked out, so the membrane has become more permeable
    • Less pigment has leaked out, so the membrane has become less permeable

12. Why does a high concentration of ethanol increase the permeability of cell membranes?

    • Ethanol increases the thickness of the bilayer, which reduces the movement of molecules across it
    • Ethanol strengthens the bilayer by forming covalent bonds with the phospholipid tails
    • Ethanol dissolves lipids and disrupts the phospholipid bilayer, making it leaky
    • Ethanol converts all membrane proteins into carbohydrates, which then block the pores

13. Which of these is a reason that membranes become more permeable at high temperatures?

    • Water in the cell freezes, which forms ice crystals that create a more effective barrier to diffusion
    • The phospholipid bilayer becomes more rigid and tightly packed, which increases permeability
    • Cholesterol is destroyed by heat, so the bilayer becomes stronger and more impermeable
    • The phospholipid bilayer becomes more fluid and proteins may denature, disrupting the membrane

14. In an experiment, membrane permeability is investigated using beetroot discs in water at different temperatures. Which variable must be kept constant to make the results valid?

    • The type of container, which should be changed to test whether it affects the result
    • The colour of the beetroot, which should be different for each temperature tested
    • The volume of water, the size of the discs and the time of immersion
    • The number of discs, which should vary to see the effect on the colour of the solution

15. Which statement about the phospholipid bilayer is correct?

    • It is freely permeable to all water-soluble substances, such as glucose and ions, by simple diffusion
    • It is a barrier to most water-soluble substances, but allows small non-polar molecules to pass through
    • It is permeable only to very large molecules, which pass through the gaps between the tails
    • It allows only charged ions to pass through, and rejects all non-polar molecules completely

16. Why do cell membranes contain proteins that bind specific molecules?

    • They replace phospholipids in the membrane, which are unable to carry any molecules across it
    • They allow selective transport of molecules that cannot cross the bilayer on their own
    • They make the membrane fully impermeable, so that the cell can store substances safely
    • They provide energy to the membrane by breaking down glucose into carbon dioxide and water

17. Which of these best describes passive transport?

    • Bulk movement of substances into or out of the cell in vesicles that fuse with the membrane
    • Movement of substances against a concentration gradient using energy released from ATP
    • Movement of substances across a membrane down a concentration gradient without the direct use of ATP
    • Movement of water through the membrane only in the presence of glycogen as a carrier molecule

18. Which part of a phospholipid molecule is hydrophilic?

    • The cholesterol molecules embedded within the bilayer
    • The phosphate-containing head group
    • The long fatty acid tails
    • The hydrocarbon chains that form the core of the bilayer

19. What is the main reason that small non-polar molecules such as oxygen can diffuse directly through the bilayer?

    • They are carried by carrier proteins that span the whole bilayer
    • They dissolve in the hydrophobic core of the bilayer
    • They are charged, so they are attracted to the phosphate heads of the phospholipids
    • They pass through aquaporins that are present within the bilayer

20. Which change would most likely increase the fluidity of a phospholipid bilayer?

    • Lowering the temperature to near freezing so that the lipids are held rigidly in place
    • Adding more glycoproteins to the outer surface of the membrane to increase its rigidity
    • Increasing the proportion of saturated fatty acid tails, which pack tightly together
    • Increasing the proportion of unsaturated fatty acid tails, which have kinks that disrupt packing

Related quizzes

• Gas exchange surfaces and Fick's Law Quiz · 2.1.1 · 20 questions
• Osmosis, diffusion and membrane transport Quiz · 2.1.3 · 20 questions
• Nucleotides, DNA and RNA structure Quiz · 2.2.1 · 20 questions
• Transcription, translation, the genetic code and genes Quiz · 2.2.2 · 20 questions
• Amino acids, polypeptides and protein structure Quiz · 2.3.1 · 20 questions
• Globular and fibrous proteins: haemoglobin and collagen Quiz · 2.3.2 · 20 questions
• Enzyme mechanism, specificity and activation energy Quiz · 2.3.3 · 20 questions
• DNA replication and the Meselson and Stahl experiment Quiz · 2.4.1 · 20 questions
• Mutations and cystic fibrosis Quiz · 2.4.2 · 20 questions
• Monohybrid inheritance and pedigree diagrams Quiz · 2.5.1 · 20 questions