HSC Biology — Module 1
Membrane Transport — Flashcards & Quiz
Cell membranes regulate what enters and leaves the cell, and HSC Biology Module 1 expects you to distinguish passive mechanisms (diffusion, osmosis, facilitated diffusion) from active transport and bulk transport. Exam questions typically give a scenario — glucose uptake, ion channels, water balance — and ask you to identify the mechanism, justify the energy requirement, and link it back to the fluid mosaic structure.
Key Points
- Simple diffusion moves small non-polar molecules (O₂, CO₂) down their concentration gradient directly through the phospholipid bilayer — no energy, no protein.
- Osmosis is the diffusion of water across a semi-permeable membrane from low to high solute concentration; aquaporins accelerate it in animal cells.
- Facilitated diffusion uses specific channel or carrier proteins for ions and polar molecules; still passive, still down the gradient.
- Active transport (e.g. sodium-potassium pump) moves substances AGAINST the gradient using ATP; essential for nerve impulse generation and nutrient absorption.
- Endocytosis (phagocytosis for large particles, pinocytosis for fluids) brings material in via membrane invagination; exocytosis releases it.
- Exam trap: "passive" just means no ATP required — it does NOT mean "no protein involved". Facilitated diffusion uses proteins but no ATP.
Common Mistakes to Avoid
- Claiming facilitated diffusion uses ATP — it doesn't. It uses proteins but no energy.
- Confusing osmosis (water movement) with diffusion (solute movement).
- Forgetting that active transport moves AGAINST the gradient (that's why it needs ATP).
- Mixing up hypotonic (cell swells), isotonic (no change), hypertonic (cell shrinks) environments.
- Ignoring the role of protein channels in allowing polar/charged molecules to cross.
Exam Strategy
HSC Module 1 membrane transport questions give a scenario (glucose uptake, kidney reabsorption, plant root water uptake) and ask you to identify the mechanism. Method: (1) identify whether the substance moves with or against its gradient, (2) determine if ATP is needed, (3) select the mechanism, (4) link to membrane structure (bilayer for non-polar, channels for polar, pumps for active).
Sample Flashcards
Q1: Define diffusion and give one biological example.
Diffusion is the net movement of particles from a region of high concentration to low concentration down the concentration gradient, requiring no energy.
Q2: What is osmosis?
Osmosis is the net movement of water molecules from a region of low solute concentration to high solute concentration across a selectively permeable membrane.
Q3: Explain facilitated diffusion.
Facilitated diffusion is passive transport of molecules across the membrane through specific carrier or channel proteins, moving down the concentration gradient without energy input.
Q4: How does active transport differ from passive transport?
Active transport moves substances against their concentration gradient (low to high) and requires energy (ATP). Passive transport moves substances down the gradient without energy.
Q5: Define endocytosis and exocytosis.
Endocytosis: the cell membrane folds inward to engulf substances into a vesicle (phagocytosis for solids, pinocytosis for liquids). Exocytosis: vesicles fuse with the membrane to release contents outside the cell.
Sample Quiz Questions
Q1: Diffusion requires energy input from the cell (ATP).
Answer: FALSE
Diffusion is a passive process that does not require ATP. Particles move down their concentration gradient due to their own kinetic energy.
Q2: Osmosis is the movement of water from a region of low solute concentration to high solute concentration across a selectively permeable membrane.
Answer: TRUE
Osmosis specifically involves water moving across a selectively permeable membrane towards the region of higher solute concentration.
Q3: Facilitated diffusion uses carrier or channel proteins and requires ATP.
Answer: FALSE
Facilitated diffusion uses carrier or channel proteins but is still passive — it moves molecules DOWN their concentration gradient without ATP.
Revision Tip
Transport mechanism selection is pattern recognition — use Revizi flashcards that give scenarios and ask for the correct mechanism.
Related Concepts
Last updated: March 2026 · 6 flashcards · 6 quiz questions