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Understanding Passive Transport: Diffusion and Osmosis in Cell Membranes

Passive transport is the movement of materials across cell membranes without the use of cellular energy. It involves processes like simple diffusion, facilitated diffusion, and osmosis. In simple diffusion, small particles move through the plasma membrane, influenced by temperature and concentration gradients until dynamic equilibrium is achieved. Facilitated diffusion involves larger molecules and ions passing through protein channels. Osmosis specifically refers to the diffusion of water across a semi-permeable membrane. Understanding these mechanisms is crucial for grasping how substances balance in biological systems.

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Understanding Passive Transport: Diffusion and Osmosis in Cell Membranes

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  1. Transport of Materials Passive Transport

  2. Passive Transport • Movement of materials that does not require energy from the cell. • Cell membranes are selectively permeable • Allows only certain materials to pass through • Particles move across a concentration gradient • Move from an area of high concentration to an area of low concentration.

  3. Simple Diffusion • Movement of small particles directly through the plasma membrane • Speed of diffusion depends on • Temperature • Faster at higher temperatures • Difference in concentrations • Faster with greater difference • Molecules move until dynamic equilibrium is reached • State of balance where particles are equal in concentration in all directions.

  4. Facilitated Diffusion • Movement of larger molecules or charged ions through protein channels • Ions are molecules in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative charge. • Essential chemicals travel this way glucose, sodium ions, chloride ions

  5. Facilitated Diffusion – Cont’d • Pore proteins • Allows passage of small ions across concentration gradient • Carrier Proteins • Special protein gates openand closeto allow passage.

  6. Osmosis • Diffusion of water • Semi-permeable membrane prevents movement of solute molecules • Water molecules move to even out the concentrations

  7. Osmosis cont’d • Osmosis occurs whenever there is a solute concentration difference • Special terms used to compare solutions • Isotonic - two solutions with the same solute concentration • Hypertonic – a solution with a higher solute concentration • Hypotonic – a solution with a lower solute concentration.

  8. Osmosis – cont’d • What happens to cells placed in solutions? • Animal cells • Plant cells

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