Biology: Transport across the membrane

Question 1

Definition: Diffusion

Answer 1

Net (overall) movement of molecules or ions from a region of high concentration to a region of low concentration. Diffusion will always take place when their is a concentration gradient and will continue untill equilibrium is reached.

Question 2

Definition: Facilitated diffusion

Answer 2

Hydrophilic (polar) molecules cannot diffuse through the phospholipid bilayer as they are insoluable in lipids, therefore the hydrphobic tails of the phospholipids prevent diffusion. They travel across the membrane through channel proteins.

Question 3

Definition: Osmosis

Answer 3

The net movement of free water molecules from a solution with a lower solute concentration to a solution with a higher solute concentration.

Question 4

Definition: Active transport

Answer 4

Movement of substances against the concentration gradient. Requires energy from ATP. Takes place using carrier proteins.

Question 5

Definition: Exocytosis

Answer 5

Vesicles (small membrane bound sacs containing the substance) fuse with the cell membrane and the contents are released.

Question 6

Definition: Endocytosis

Answer 6

Substances are engulfed by vesicles formed in the cell membrane and taken into the cell.