Diffusion and osmosis Flashcards
What is passive transport?
Passive transport is the movement of molecules across the membrane from areas of higher concentration to areas of lower concentration. It does not require energy input from the cell. It may also be described as the diffusion of molecules across a membrane.
What is diffusion?
Diffusion is the movement of molecules in a fluid or gas from a region of higher concentration to a region of lower concentration. It results from the natural motion of particles, which causes molecules to collide and scatter.
Concentration is the number of molecules of a substance in a given volume, and it can vary from one region to another. A concentration gradient is the difference in the concentration of a substance from one location to another.
What is osmosis?
Osmosis is the movement of molecules across a semipermeable membrane from an area of higher concentration to an area of lower concentration. It is important to recognize that the higher the concentration of solute molecules in a solution, the lower the concentration of the solvent molecules in the same solution.
Which types of solutions exist?
A solution may be described as isotonic, hypertonic or hypotonic:
1. Isotonic > A solution is isotonic to a cell if it has the same concentration of solutes as the cell. Equal amounts of water enter and exit the cell, so the size stays constant.
- Hypertonic > A hypertonic solution has more solutes than a cell. Overall, more water exits a cell in hypertonic solution, causing the cell to shrivel or even die.
- Hypotonic > A hypotonic solution has fewer solutes than a cell. Overall, more water enters a cell in hypotonic solution, causing the cell to expand or even burst.
What is facilitated diffusion?
Some molecules cannot easily diffuse across a membrane. They may cross more easily through transport proteins - openings formed by proteins that pierce the cell membrane. Facilitated diffusion enables molecules that cannot directly cross the phospholipid bilayer to diffuse through transport proteins in the membrane.
REMEMBER!
Materials move across membranes because of concentration differences!
Diffusion and osmosis are types of passive transport!
Some molecules diffuse through transport proteins!
