Topic 4: Cell Membranes and Transport Flashcards
Definitions I:
(a) Phospholipid bilayer
(b) Fluid mosaic model
(c) Cell signalling
(a) Phospholipid bilayer: Double layer of phospholipids forming membrane.
(b) Fluid mosaic model: Fluid lipids with embedded proteins.
(c) Cell signalling: Ligands binding receptors for response.
Describe the fluid mosaic model of a nerve cell membrane. [2 Marks]
Phospholipids form bilayer via hydrophobic tails (1 mark); Proteins scattered, fluid and mosaic (1 mark). (2 marks)
Outline the arrangement of cholesterol and glycoproteins in a white blood cell membrane. [2 Marks]
Cholesterol between phospholipids, stabilises (1 mark); Glycoproteins on surface, recognition/signalling (1 mark). (2 marks)
State the roles of:
(a) Phospholipids [1 Mark]
(b) Cholesterol [1 Mark]
(c) Glycoproteins [1 Mark]
(a) Phospholipids: Form bilayer, barrier stability. (1 mark)
(b) Cholesterol: Regulates fluidity, stability. (1 mark)
(c) Glycoproteins: Cell recognition, signalling. (1 mark)
In insulin signalling, outline the main stages of cell signalling to glucose uptake. [3 Marks]
Insulin secreted by pancreas (1 mark); Transported to muscle, binds receptors (1 mark); Triggers glucose uptake (1 mark). (3 marks)
In a lung cell, explain facilitated diffusion and active transport. [2 Marks]
Facilitated: O₂ via channels, no energy (1 mark); Active: Na⁺/K⁺ pump, uses ATP (1 mark). (2 marks)
Definitions II:
(a) Diffusion
(b) Osmosis
(c) Active transport
(a) Diffusion: Movement from high to low concentration. (1 mark)
(b) Osmosis: Water diffusion across semi-permeable membrane. (1 mark)
(c) Active transport: Movement against gradient using ATP. (1 mark)
Describe endocytosis and exocytosis in a macrophage engulfing bacteria. [2 Marks]
Endocytosis: Membrane engulfs bacteria, forms vesicle (1 mark); Exocytosis: Vesicle fuses, expels waste (1 mark). (2 marks)
In a lab, investigate diffusion using agar cubes of different sizes. [3 Marks]
Cut agar cubes (1-3 cm), add dye (1 mark); Measure penetration rate (1 mark); Smaller cubes faster (1 mark). (3 marks)
Calculate the surface area to volume ratio of a 2 cm cube vs. a 4 cm cube. [2 Marks]
2 cm: SA=24 cm², V=8 cm³, 3:1 (1 mark); 4 cm: SA=96 cm², V=64 cm³, 1.5:1 (1 mark). (2 marks)
Using dialysis tubing, outline osmosis in a model cell with sucrose solutions. [2 Marks]
Fill tubing with sucrose, place in water (1 mark); Water enters, tubing swells (1 mark). (2 marks)
In potato tissue, investigate the effect of surface area on dye diffusion rate. [3 Marks]
Cut potato cubes, immerse in dye (1 mark); Measure diffusion depth (1 mark); Smaller cubes faster (1 mark). (3 marks)
Using onion cells, determine water potential with different sucrose solutions. [3 Marks]
Place onion in sucrose solutions (0-1 M) (1 mark); Observe plasmolysis (1 mark); Estimate water potential (1 mark). (3 marks)
State the roles of:
(a) Glycolipids [1 Mark]
(b) Carrier proteins [1 Mark]
(c) Channel proteins [1 Mark]
(a) Glycolipids: Cell recognition, stability. (1 mark)
(b) Carrier proteins: Active/facilitated transport. (1 mark)
(c) Channel proteins: Facilitated diffusion, ions. (1 mark)
Explain water movement in plant root cells vs. animal red blood cells in saline. [4 Marks]
Root: Water in, turgid, wall supports (1 mark); RBC: Water out, shrivels, no wall (1 mark); Water potential drives (1 mark); Osmosis differs (1 mark). (4 marks)
Analyse how cholesterol and proteins affect membrane fluidity and transport. [4 Marks]
Cholesterol reduces fluidity, stabilises (1 mark); Proteins enable transport, e.g., carriers (1 mark); Channels allow diffusion (1 mark); Balance fluidity/permeability (1 mark). (4 marks)
