Diffusion 5.3 Flashcards
Passive Movement
All movement requires energy, but passive movement utilised the energy and moves with the natural flow of the particles
Active Movement
Using energy from an additional source and moving the particles against their natural way of movement
Diffusion
The net movement of particles from an area of high concentration to an area of low concentration down a concentration gradient until there is complete equilibrium.
Is diffusion better over short or long distances?
The rate of diffusion will be faster over a short distance because the particles are always colliding which slows down the rate of diffusion, so shorter distances means there’s less time to collide.
Factors affecting diffusion rates
Higher temperature means the particles have more kinetic energy and will diffuse faster.
If the concentration difference is higher, then the overall movement from high to low will be larger so faster.
Simple diffusion
Diffusion when there are no barriers to be considered.
How to calculate the rate of diffusion.
distance travelled/time or volume filled/time
How to calculate volume and SA of a cube?
Volume = side cubed SA= 6 x sides squared
How do particles diffuse across membranes?
Non-polar molecules can easily diffuse through the phospholipid bilayer as they can interact with the hydrophobic core so can be let through
Why is a plasma membrane selectively permeable?
Because some small polar molecules can diffuse through but very slowly, and the bigger polar molecules cannot diffuse through. All non-polar molecules can diffuse through so it is selective about what can come in and out of the cell.
What affects the rate at which particles diffuse across a membrane?
The surface area as the bigger it is, the more particles will diffuse across.
The thickness of the membrane as the thicker it is, the longer the particles have to travel to diffuse into the cell so the slower they will go.
Facilitated Diffusion
Diffusion across a membrane through an intrinsic channel protein. Used mainly for polar molecules and ions.
Factors Affecting Facilitated Diffusion
Temperature, Distance to travel, Thickness of membrane and Surface area are all still factors as well as the number of channel proteins available.
Investigating diffusion rates
You can use dialysis tubing to mimic a cell membrane. Tye it to a glass rod and tye at the end. Put it into a glucose and starch solution and wait for it to diffuse. Then test for glucose in the dialysis tubing and starch in the remaining solution.
