Passive Membrane Transport

Passive membrane transport is a movement of ions and other atomic or molecular substances across cell membranes without need of energy input. Unlike active transport, it does not require an input of cellular energy because it is instead driven by the tendency of the system to grow in entropy.

• Diffusion: The movement of particles along a concentration gradient from high concentration to low concentration.
• The particles spread until they fill all available space evenly.
• Diffusion does not require energy
• Particles move due to kinetic energy
• Molecules will always move down the concentration gradient, toward areas of lesser concentration.
• Particles move in an attempt to reach equilibrium making the distribution of particles the same through all available space.
• If permeable membrane separates the concentrations, the particles will attempt-?
• Diffusion across a membrane is called Passive Transport because it does not require energy
• Some particles pass freely through the semipermeable plasma membrane composed of a bi-lipid layer and proteins
• Molecules move through the membrane from high to low concentration.
• Larger molecules may move through the protein channels

• Osmosis: Is the type of passive transport that involves only the movement of water
• Water will always move from high to low concentration or toward the higher solute concentration.
• It is assumed that during osmosis only water can move and not other types of molecules
• The simple rule is is that salt sucks
• Hypotonic Solution- Water is going to move in
• Isotonic Solution- Balanced
• Hypertonic Solution- Out
• Hypertonic Solutions:
• Water moves into the cell
• As the water enters the cell will swell
• An animal cell may continue to swell until it bursts aka Cytolysis
• A plant cell can only swell until it reaches the cell wall resulting in tightening of the cell wall and outward pressure called turgor pressure.
• As water exits the cell the cell will shrink, this is called Plasmolysis
• Plasmolysis causes an animal cell to dehydrate
• Isotonic Solution:
• Water enters and exits the cell at equal rates

What I learned about this subject was that there is a scientific explanation to why anything moves. Osmosis is for the movement of water and Diffusion is everything else (as long as you're not using energy.). It surprised me that a cell is able to burst when put into distilled water. I did not know about this subject until this year. I enjoyed learning about this because it is a quick and easy objective to learn and understand. This can be applied outside biology when I'm trying to move something, and I can determine if it needs energy to move or not.

By: Corban Mills

Mr. Black's class notes