Diffusion Flashcards
Define simple diffusion.
The net movement, as a result of the random motion of its molecules or ions, of a substance from a region of its higher concentration to a region of its lower concentration.
What causes movement of particles in diffusion?
Kinetic energy.
After a period of time, what is established between the high and low concentration?
Equilibrium
What does ‘passive process’ mean?
It does not require energy from an external source such as ATP.
Why can water simply diffuse across the cell membrane despite being polar?
It is very small
Why can molecules such as oxygen and CO2 diffuse simply across the cell membrane?
They are very small and uncharged.
Name 4 factors that affect the rate of diffusion.
Steepness of concentration gradient
Temperature
Surface area
Size of molecules and charges of ions
Describe how the steepness of the concentration gradient affects rate of diffusion.
If there are more molecules on one side of a membrane, more molecules are likely to move randomly to the region with fewer molecules. Movement of more molecules means faster diffusion.
Describe how temperature leads to faster rate of diffusion.
Increased temperature increases the kinetic energy of particles therefore they move faster, leading to faster rate of diffusion.
Describe how greater surface area leads to a faster rate of diffusion.
The greater the surface area, the more room for molecules that can diffuse at a time
Describe how a smaller surface area to volume ratio leads to a decrease in diffusion.
As organisms get larger, surface area to volume ratio decreases. Therefore, this slows the rate at which substances can diffuse.
Describe how the size of an ion or molecule can affect the rate of diffusion.
Larger molecules take longer to diffuse as they require more energy to move. They also require a channel or carrier protein to help them cross the membrane. Charged ions also require a channel protein.
Non polar small molecules diffuse more quickly as they can pass directly through the cell surface membrane
What is facilitated diffusion?
Name the proteins it uses.
Diffusion that requires the assistance of channel or carrier proteins as the molecules are charged or too large to diffuse across the cell membrane.
Is facilitated diffusion active or passive?
Passive, relies on kinetic energy only.
Describe channel proteins.
Pores in the cell surface membrane that allow water soluble molecules to diffuse in/out of the cell.
They may be gated.
