(d)+Passive+Transport

**Passive Transport**
(1) Carefully define the terms **diffusion** & **osmosis**.

Diffusion is a movement of any particles from a region with higher concentration of that particles to region with lower concentration of that particles (by Haruka)

Osmosis is a movement of water molecules across the semi permeable membrane, from an area with higher water potential (therefore low solute concentration) to an area with lower water potential (therefore high solute concentration) and this happens until equilibrium is reached, a state where water potential on both sides of the semi-permeable membrane becomes equal.(by Haruka)

(2) As a general rule, which substances can diffuse across a cell membrane and which substances cannot?

Only small and neutral/uncharged particles can diffuse across the plasma membrane without requiring energy. So objects which are too large to fit in through the gaps between phospholipid molecules and charged particles which will be repelled by slightly charged tails of phospholipid molecules cannot diffuse across a plasma membrane, but only by with an use of energy. (by Haruka)

(3) What is meant by **facilitated diffusion**? Does it require an energy input? Describe the process.

Facilitated diffusion (not to be confused with a diffusion of particles) is a type of passive transport which allows the substances that are too big to cross the plasma membrane or charged so that it gets repelled by the tails of phospholipid molecules to go across the cell membrane, with a help from special transport proteins. These special transport proteins embed in the cell membrane between the bunch of phospholipid molecules to create a tunnel-like space for substances to cross through the membrane. Since facilitated diffusion is a type of passive transport, it does not require energy.(by Haruka)