Cells - Transport Across Membranes: Diffusion Flashcards
Define diffusion
The net movement of molecules from a region of high concentration to a region of low concentration until evenly distributed.
What type of transport is diffusion?
Passive transport
What is the energy. source for diffusion?
The inbuilt kinetic energy of the diffusing particles.
Does diffusion occur between different concentrations of different substances of the same substance?
The same substance.
What can cross membranes through simple diffusion?
Small, non-polar molecules like oxygen and carbon dioxide.
What substances can cross membranes by facilitated diffusion?
Charged ions and polar molecules.
Where on the plasma membrane does facilitated diffusion occur?
At specific points where specific protein molecules are present.
What are carrier proteins?
Transport proteins spanning the plasma membrane.
What type of molecules do carrier proteins move?
Large molecules (down their concentration gradient)
Can any molecule bind to any carrier protein?
No, carrier proteins are selective, each binding with a specific molecule.
How do carrier proteins facilitate diffusion?
1) A large molecule binds to a specific carrier protein.
2) The carrier protein changes shape.
3) This releases the molecule on the opposite side of the membrane.
What are channel proteins?
Water-filled hydrophilic channels forming pores in the membrane.
What substances do channel proteins facilitate the diffusion of?
Specific water soluble substances.
Can any ion pass through any channel protein?
No, channel proteins are selective.
What does the selectivity of channel proteins allow them to do?
Control the entry and exit of ions.
