Noesis
Level 1 — RecognitionCell Membrane & Transport

Cell Membrane & Transport

⏱ 20 minutes30 marksprintable — key stays hidden on paper

Level 1: Recognition

Time Limit: 20 minutes Total Marks: 30

Section A — Multiple Choice (choose ONE correct option)

(1 mark each, 10 marks)

Q1. The fluid mosaic model describes the cell membrane as: a) A rigid layer of protein sheets b) A fluid phospholipid bilayer with embedded proteins c) A solid single layer of lipids d) A carbohydrate mesh

Q2. In the phospholipid bilayer, the hydrophobic tails point: a) Outward toward water b) Toward each other, away from water c) Toward the cell nucleus d) In random directions

Q3. Integral (intrinsic) membrane proteins are best described as: a) Loosely attached to the membrane surface b) Embedded within/spanning the bilayer c) Found only inside the cytoplasm d) Made of carbohydrate only

Q4. The main role of cholesterol in animal cell membranes is to: a) Transport glucose actively b) Regulate membrane fluidity and stability c) Act as a receptor for hormones only d) Provide energy for the cell

Q5. Which process requires ATP? a) Simple diffusion b) Osmosis c) Active transport d) Facilitated diffusion

Q6. Osmosis is the movement of water from a region of: a) High solute to low solute concentration b) High water potential to low water potential c) Low water potential to high water potential d) High to low temperature

Q7. A red blood cell placed in a hypotonic solution will: a) Shrink (crenate) b) Swell and possibly lyse c) Stay the same d) Become turgid

Q8. The sodium-potassium pump moves: a) 3 Na⁺ out and 2 K⁺ in per ATP b) 2 Na⁺ out and 3 K⁺ in per ATP c) 3 K⁺ out and 2 Na⁺ in per ATP d) Only water molecules

Q9. Phagocytosis is best described as: a) Cellular "drinking" of liquids b) Cellular "eating" of large solid particles c) Bulk secretion out of the cell d) Passive diffusion of ions

Q10. Exocytosis is used mainly to: a) Take in large particles b) Release/secrete materials out of the cell c) Break down worn organelles d) Move ions against a gradient passively

Section B — Matching

(1 mark each, 6 marks)

Q11. Match each term (i–vi) to its correct description (A–F).

Term Description
(i) Peripheral protein A. Uses energy from an ion gradient made by another pump
(ii) Channel protein B. Loosely bound to membrane surface
(iii) Secondary active transport C. Forms a hydrophilic pore for ions
(iv) Isotonic solution D. Uptake of specific molecules using receptors
(v) Receptor-mediated endocytosis E. No net water movement in/out of cell
(vi) Plasmolysis F. Membrane pulls away from cell wall in plants

Section C — True/False WITH Justification

(2 marks each: 1 for T/F, 1 for justification, 14 marks)

Q12. Simple diffusion moves substances down their concentration gradient without membrane proteins.

Q13. Facilitated diffusion requires ATP because it uses proteins.

Q14. A plant cell in a hypertonic solution becomes turgid.

Q15. Selective permeability means the membrane allows all substances to pass equally.

Q16. Water potential of pure water is set at zero, and adding solute makes it more negative.

Q17. Cholesterol prevents the membrane from becoming too fluid at high temperatures.

Q18. During exocytosis, a vesicle fuses with the plasma membrane to release its contents.

Answer keyMark scheme & solutions

Section A (1 mark each)

Q1 — b. The model is "mosaic" (proteins scattered like tiles) and "fluid" (lipids move laterally). (1)

Q2 — b. Hydrophobic (water-fearing) tails cluster inward; hydrophilic heads face the watery interior/exterior. (1)

Q3 — b. Integral proteins are embedded in or span the hydrophobic core; peripheral ones sit on the surface. (1)

Q4 — b. Cholesterol buffers fluidity — restricts movement at high temp, prevents packing at low temp; adds stability. (1)

Q5 — c. Active transport moves solutes against the gradient, needing ATP. Options a, b, d are passive. (1)

Q6 — b. Osmosis = net water movement from high to low water potential (high→low free water). (1)

Q7 — b. Hypotonic surroundings → water enters cell → RBC swells and can burst (lysis/haemolysis). (1)

Q8 — a. Standard Na⁺/K⁺-ATPase stoichiometry: 3 Na⁺ out, 2 K⁺ in per ATP hydrolysed. (1)

Q9 — b. Phago = "eat"; engulfing large solid particles into a vesicle. (1)

Q10 — b. Exocytosis exports/secretes materials via vesicle fusion. (1)

Section B — Matching (1 mark each)

Q11:

  • (i) → B (peripheral = loosely surface-bound)
  • (ii) → C (channel = hydrophilic pore)
  • (iii) → A (secondary active transport uses an ion gradient)
  • (iv) → E (isotonic = no net water movement)
  • (v) → D (receptor-mediated = specific uptake via receptors)
  • (vi) → F (plasmolysis = membrane pulls from wall)

6 marks total, 1 each.

Section C — True/False + Justification (2 marks each)

Q12 — TRUE (1). Justification: Small non-polar/lipid-soluble molecules cross the bilayer directly, high→low, no proteins or energy needed. (1)

Q13 — FALSE (1). Justification: Facilitated diffusion is passive — proteins provide a route but movement is down the gradient; no ATP is used. (1)

Q14 — FALSE (1). Justification: In hypertonic solution water leaves the cell → plasmolysis (flaccid/plasmolysed), not turgid. Turgid occurs in hypotonic solution. (1)

Q15 — FALSE (1). Justification: Selective/differential permeability means only certain substances pass; the membrane controls entry/exit, not equal passage for all. (1)

Q16 — TRUE (1). Justification: Ψ of pure water = 0 kPa; adding solute lowers (makes negative) the solute potential, so water potential becomes negative. (1)

Q17 — TRUE (1). Justification: At high temperature cholesterol restrains phospholipid movement, reducing excess fluidity and keeping the membrane stable. (1)

Q18 — TRUE (1). Justification: Vesicle membrane fuses with the plasma membrane, expelling contents outside — the definition of exocytosis. (1)

[
  {"claim":"Na/K pump net charge exported per cycle is +1 (3 Na out, 2 K in)","code":"na_out=3; k_in=2; net_positive_charge_out=na_out - k_in; result = (net_positive_charge_out == 1)"},
  {"claim":"Total marks sum to 30","code":"sectionA=10*1; sectionB=6*1; sectionC=7*2; total=sectionA+sectionB+sectionC; result = (total == 30)"},
  {"claim":"Pure water potential is 0 and solute addition gives negative value","code":"psi_pure=0; solute_potential=-200; psi_solution=psi_pure+solute_potential; result = (psi_solution < psi_pure)"},
  {"claim":"Section C has 7 questions at 2 marks each = 14","code":"n=7; per=2; result = (n*per == 14)"}
]