Diffusion Flashcards
What is simple diffusion?
The movement of substances from an area of high concentration to an area of low concentration, down a concentration gradient across a partially permeable membrane directly through the phospholipid bilayer
Is energy from ATP required?
No, it is a passive process
What is dynamic equilibrium?
Where there is movement of molecules but there is no net change of concentration between the different locations
What are the molecules that can diffuse through the bilayer?
• lipid soluble eg steroid hormone
• small and non polar eg CO2
• very small and polar (slowly) eg water
What factors affect the rate of diffusion?
- Temperature
- Conc gradient
- Thickness of exchange surface
- Surface area
How does temperature affect the rate of diffusion?
The higher the temperature the more kinetic energy - the faster the molecules move so rate of diffusion increases
How does concentration gradient affect the rate of diffusion?
The steeper the gradient the faster the rate of diffusion
High = faster
How does the thickness if exchange surface affect the rate of diffusions?
Longer distances= longer diffusion pathway
Shorter distances = shorter diffusion pathway
How does surface area affect the rate of diffusion?
Larger surface area = faster rate
What is facilitated diffusion?
Movement of substances from an area of high concentration to an area of low concentration down a concentration gradient across the membrane via carrier or channel proteins
What is facilitated diffusion limited by?
The number of carrier/channel proteins in the membrane
Does facilitated diffusion require energy from ATP?
No
What is the role of channel proteins in facilitated diffusion?
• Act as pores in the membrane, some only allow specific ions through
Eg Na ions (due to specific shape)
• they can be gated so they only open/close in specific circumstances
What is the role of carrier proteins in facilitated diffusion?
• allow specific large molecules to pass through
• when the molecule binds to a specific site on the carrier, the protein changes shape and transfers the molecule to the other side of the membrane
Different membranes around different cells can have ……… channels and carrier proteins in their bilayer and so can control the entry and exit of different substances into and out of the cell
Different
What factors affect the rate of facilitated diffusion?
1) conc gradient
2) temperature
3) number of channel of carrier proteins
How do you calculate the rate of diffusion?
