Cell Membrane Processes: Diffusion and Osmosis

Cell Membrane Processes

• Focus on key processes at the cell membrane: diffusion and osmosis

• Diffusion: Movement of molecules from an area of high concentration to low concentration

  • Molecules that can't pass through a semipermeable membrane prompt water to move instead (osmosis).

Key Concepts

General Terms

• Solute: Substance dissolved in a solution (e.g., salt in saltwater).

• Solvent: The dissolving medium, often water (known as the universal solvent).

• Solution: Mixture of solute and solvent (e.g., saltwater).

• Concentration: Amount of solute in a solution, affecting flavor, strength, etc., similar to making Kool-Aid.

• Concentration Gradient: Difference in concentration between two areas, like a steep hill (e.g., high concentration on one side and low concentration on the other).

Molecular Motion

• Brownian Motion: Molecules are in constant motion, even in solids, which allows diffusion to occur.

  • Molecular movement is more pronounced in liquids and gases than in solids.

Diffusion Explained

• Movement of molecules occurs along the concentration gradient:

  • High concentration area to low concentration area.

• Example of diffusion:

  • Breathing in oxygen: Oxygen diffuses from the lungs (high concentration) to the bloodstream (lower concentration), facilitating gas exchange.

• No Energy Required: Diffusion is a passive process, occurring naturally without energy input, allowing survival and mobility.

  • Essential for organisms to uptake nutrients and oxygen effortlessly.

Equilibrium

• Equilibrium: Achieved when solute concentration is equal on both sides of a semipermeable membrane.

  • Molecules will continue to move back and forth, maintaining equilibrium.

Osmosis Defined

• Osmosis: Specific type of diffusion pertaining to water.

  • Water moves from a region of high water concentration (low solute concentration) to low water concentration (high solute concentration) to achieve equilibrium.

  • Example: Adding water to a concentrated drink dilutes the concentration, analogous to osmosis balancing solute concentrations.

Importance of Membrane Permeability

• Not all molecules can pass the membrane (e.g., too large or charged) leading to the need for osmosis.

• Water Movement: If solutes cannot cross the membrane, water moves instead to balance concentrations.

Analogies and Everyday Examples

• Classroom analogy: Students crammed to one side and allowed to spread out shows diffusion towards filling available space.

• Real-life illustration: Food coloring diffusing in water or scent spreading in a room demonstrates continuous diffusion.

Recap

• Diffusion: Movement from high concentration to low concentration due to random particle motion.

• Osmosis: Movement of water, focusing on achieving equilibrium by balancing solute concentrations.