Topic 2: Passive Transport

a concentration gradient is

formed when the concentration of a particle is higher in one area than in another

a particle moving along (or down) its concentration gradient is (passive transport)

moving from an area of high concentration to an area of low concentration

a particle moving against (or up) its concentration gradient is (active transport)

moving from an area of low concentration to an area of high concentration

what is passive transport?

the movement of substances across the cell membrane without the input of energy

what are the three types of passive transport?

diffusion, osmosis, and facilitated transport

what is diffusion?

the net movement of molecules (solutes, not water) down a concentration gradient; does not require energy or protein transport; high to low concentration

in diffusion, when does net movement stop?

when the molecules reach dynamic equilibrium (all areas have the same concentration) 

what is dynamic equilibrium?

molecules still move both ways, but at equal rates; solute concentration is uniform-no concentration gradient 

what is osmosis?

the diffusion of water across a selectively permeable membrane

when will osmosis occur?

when there is a concentration gradient created by a solute that cannot diffuse across the membrane

where is the net movement of water in osmosis?

towards the side with lower water concentration ( higher solute concentration)

when does dynamic equilibrium occur in osmosis?

occurs when the two solutions reach the same concentration

water diffuses in both directions at equal times

what are aquaporins?

a type of transmembrane protein; integral membrane proteins that water molecules can more easily travel through; allow water to travel more rapidly into and out of the cell than by just diffusing through the phospholipid bilayer

what are the three types of solutions in osmosis?

isotonic, hypertonic, hypotonic

what is an isotonic solution?

solute and water concentrations are equal on both sides of cellular membrane

no net gain or loss of water by the cell

what is a hypotonic solution?

concentration of solute in the solution (outside the cell) is lower than inside the cell

what is a hypertonic solution?

concentration of solute in the solution (outside the cell) is higher than inside the cel

what is facilitated transport?

same thing as simple diffusion but with the help of membrane proteins