Exchange Across Cell Membranes - Diffusion Flashcards
What is diffusion?
Diffusion is the net movement of particles (molecules or ions) from an area of higher concentration to an area of lower concentration
Which way will molecules diffuse?
Molecules will diffuse both ways, but the net movement will be to the area of lower concentration. This continues until particles are evenly distributed throughout the liquid or gas
What is a concentration gradient?
The concentration gradient is the path from an area of higher concentration to an area of lower concentration. Particles diffuse down a concentration gradient
Does diffusion require energy?
Diffusion is a passive process - no energy is required for it to happen
Can particles diffuse across the cell membrane?
Particles can diffuse across cell membranes, as long as they can move freely through the membrane i.e. they’re small enough or non-polar
When molecules diffuse directly through a cell membrane it is also known as what?
Simple diffusion
What is facilitated diffusion?
Facilitated diffusion is when large or charged particles diffuse through carrier proteins or channel proteins in the membrane
Facilitated diffusion moves particles down a what?
A concentration gradient, from a higher to lower concentration
What do carrier proteins do?
Carrier proteins move large molecules across membranes, down their concentration gradient
How do carrier proteins work?
- First, a large molecule attaches to a carrier protein in the membrane
- Then, the protein changes shape
- This releases the molecule on the opposite side of the membrane
What to channel proteins do?
Channel proteins form pores in the membrane for charged particles to diffuse through (down their concentration). Different channel proteins facilitate the diffusion of different charged particles
Give three factors which the rate simple diffusion depends on
- The concentration gradient
- The thickness of the exchange surface
- The surface area
How does the concentration gradient affect the rate of simple diffusion?
The higher the concentration gradient, the faster the rate of diffusion. As diffusion takes place, the difference in concentration between the two sides of the membrane decreases until it reaches an equilibrium. This means diffusion slows down over time
How does the thickness of the exchange surface affect the rate of simple diffusion?
The thinner the exchange surface, the faster the rate of diffusion
How does the surface area affect the rate of simple diffusion?
The larger the surface area, the faster the rate of diffusion