What is passive transport?
the diffusion of a substance across a biological membrane and does not require energy (down a concentration gradient)
What are the 5 different passive transport processes?
4. facilitated diffusion
5. countercurrent exchange
How can the rates of passive transport increase?
- higher concentration gradients
- higher temperatures
- smaller particle size
What is a concentration gradient?
The region along which the density of a substance increases or decreases, and doesn't require any work to happen. Each substance diffuses independently down its own concentration gradient and isn't affected by other substances' concentration gradients.
What is diffusion?
The net movement of substances from an area of higher concentration to an area of lower concentration. It results from random movement of molecules, but the diffusion of a population may be directional.
Is diffusion spontaneous or nonspontaneous?
spontaneous, because it doesn't require any energy
What is the difference between diffusion and osmosis?
osmosis is a type of diffusion where water diffuses across a semi-permeable membrane
What is facilitated diffusion?
the diffusion of solutes or water through channel proteins or carrier proteins in the plasma membrane (the lipid bilayer does not allow polar molecules and ions to go through)
Why is facilitated diffusion considered passive transport?
Because the solute is moving down its concentration gradient, a process requiring no energy. (Also, it speeds the transport of a solute by providing passage through the membrane without altering the direction of transport.)
What are transport proteins?
a transmembrane protein that helps a specific substance to cross the membrane
What are the two types of transport proteins?
channel: provides a hydrophilic tunnel to allow specific molecules to pass the membrane
carrier: binds to molecule and changes shape as it moves a solute across the membrane
Both proteins can transport the solute in either direction, but the net movement is down the concentration gradient of the solute.
What are the channel proteins that transport ions called?
ion channels, which function as gated channels that open or close in response to a chemical or electrical stimulus (some ions include: Na+, K+, Ca2+, or Cl-)
What specialized type of channel protein facilitates the movement of water across the plasma membrane?
What do carrier proteins facilitate the movement of?
the movement of ions AND some larger organic molecules, such as amino acids and glucose
What happens when the concentration gradient is greater?
The initial rate of diffusion is faster. However, equilibrium is reached sooner when the concentration gradient is smaller due to the fewer number of solutes necessary to establish equilibrium.
What happens when the temperature of solutions are greater?
The rate of diffusion is faster. Molecules at higher temperatures have more kinetic energy and move faster.
What happens when the solute weight is greater?
The rate of diffusion is slower. All molecules at the same temperature have the same average kinetic energy. But remember: kinetic energy = 1/2 x mass x velocity2. Thus, lighter molecules move faster.
Do small, noncharged particles, primarily gases (like carbon dioxide and oxygen), need facilitated diffusion?
no, they can diffuse through the plasma membrane without any help