HSC Biology — Module 1
Fluid Mosaic Model — Flashcards & Quiz
The fluid mosaic model describes the structure of the cell membrane as a dynamic phospholipid bilayer embedded with proteins, cholesterol, and carbohydrates. Understanding why the membrane is described as both "fluid" (phospholipids move laterally) and "mosaic" (diverse proteins scattered throughout) is a core HSC Biology skill. Exam questions frequently ask you to draw and label a membrane diagram, explain selective permeability, or link membrane structure to its functions in transport and cell signalling.
Key Points
- The fluid mosaic model (Singer & Nicolson, 1972) describes the membrane as a phospholipid bilayer embedded with proteins, cholesterol and carbohydrates.
- The bilayer is amphipathic: hydrophilic phosphate heads face water, hydrophobic fatty-acid tails face inward — this drives spontaneous self-assembly.
- Proteins span or sit on the membrane: integral (transmembrane channels, carriers) and peripheral (signalling, structural). Carbohydrate tags on glycoproteins enable cell recognition.
- Cholesterol buffers fluidity across temperatures — stabilises at high T, prevents packing at low T.
- Selective permeability: small non-polar molecules cross freely; large/charged molecules need channel or carrier proteins.
- Exam staple: explain how the structure supports specific functions (transport, signalling, cell recognition, endo/exocytosis).
Common Mistakes to Avoid
- Drawing the bilayer as a single layer instead of two — phospholipids must always be drawn tail-to-tail.
- Putting phosphate heads INSIDE and tails OUTSIDE — it's the opposite: hydrophilic heads face water on both surfaces, hydrophobic tails point inward.
- Claiming cholesterol makes the membrane more fluid — it actually stabilises fluidity, keeping it consistent across temperatures.
- Mixing up integral (span the bilayer) and peripheral (sit on one surface) proteins in diagrams.
- Calling the membrane "static" or "rigid" — it's called fluid because phospholipids move laterally and proteins drift within the bilayer.
Exam Strategy
HSC Module 1 fluid mosaic questions typically ask you to draw a labelled diagram and explain how the structure enables a specific function (transport, signalling, cell recognition). Drawing marks reward: bilayer clearly shown, phosphate heads labelled, hydrophobic tails shown tail-to-tail, integral proteins spanning the bilayer, carbohydrate tags on the outer surface. Then explain structure-function: "The hydrophobic core prevents charged molecules crossing, so specific transport proteins are required." Always link structure back to a specific property.
Sample Flashcards
Q1: Describe the fluid mosaic model of the cell membrane.
The membrane is a phospholipid bilayer with proteins, cholesterol and carbohydrates embedded or attached. "Fluid" because components move laterally; "mosaic" because of the varied protein pattern.
Sample Quiz Questions
Q1: The cell membrane is described as "fluid" because its phospholipid and protein components can move laterally.
Answer: TRUE
The fluid mosaic model describes the membrane as fluid because phospholipids and some proteins can drift laterally within the bilayer.
Q2: Cholesterol makes the cell membrane more rigid and less fluid at normal body temperature.
Answer: FALSE
At normal body temperature, cholesterol actually acts as a fluidity buffer — it prevents the membrane from becoming too fluid. At low temperatures it prevents solidification. It does not simply make it rigid.
Revision Tip
Structure-function links are the recurring test pattern — drill them with Revizi flashcards and then sketch the diagram from memory to build exam-speed recall.
Related Concepts
Last updated: March 2026 · 1 flashcards · 2 quiz questions