Passive Transport Across Cell Membrane
Mechanisms of movement of substances across the membrane without energy expenditure, including simple diffusion, facilitated diffusion, and osmosis.
What is Passive Transport Across Cell Membrane?
The movement of molecules across a cell membrane without the use of energy by the cell, driven by a concentration or electrochemical gradient.
Key points
- Define passive transport and its characteristics.
- Differentiate between simple diffusion, facilitated diffusion, and osmosis.
- Identify the role of membrane proteins in facilitated diffusion.
- Explain the driving force behind passive transport.
Common exam trap
Confusing passive transport with active transport (which requires energy).
Definitions
- Term
Passive Transport
- Meaning
The movement of molecules across a cell membrane without the use of energy by the cell, driven by a concentration or electrochemical gradient.
- Term
Simple Diffusion
- Meaning
The net movement of molecules from a region of higher concentration to a region of lower concentration, directly through the lipid bilayer of a membrane.
- Term
Facilitated Diffusion
- Meaning
The passive movement of molecules across a cell membrane with the assistance of specific transmembrane transport proteins (channels or carriers).
- Term
Osmosis
- Meaning
The spontaneous net movement of solvent molecules (typically water) through a selectively permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides.
- Term
Concentration Gradient
- Meaning
The gradual difference in the concentration of a substance between two areas.
Learning objectives
Define passive transport and its characteristics.
Differentiate between simple diffusion, facilitated diffusion, and osmosis.
Identify the role of membrane proteins in facilitated diffusion.
Explain the driving force behind passive transport.
Understand the factors affecting the rate of passive transport.
Prerequisites
Structure of the cell membrane (lipid bilayer, proteins).
Concept of concentration gradient.
Basic understanding of molecular kinetic energy.
Common mistakes
Confusing passive transport with active transport (which requires energy).
Assuming all molecules move freely across the membrane without protein assistance.
Not distinguishing between the movement of solutes and solvents (water) in osmosis.
Overlooking the role of concentration gradients as the driving force.
Keywords
Passive Transport
Simple Diffusion
Facilitated Diffusion
Osmosis
Cell Membrane
Concentration Gradient
Semipermeable Membrane
Channel Proteins
Carrier Proteins
Water Potential
Practice preview
Which of the following is a characteristic of simple diffusion across a cell membrane?…
easy
Which of the following statements about facilitated diffusion is INCORRECT?…
medium
Consider a cell with a high internal concentration of potassium ions (K+) and a low internal concentration of sodium ions (Na+). If this cell is placed in an environment with a low concentration of K+ and a high concentr…
hard