Transport through cell membranes 1 Transport through cell

Transport through cell membranes 1

Transport through cell membranes • The cell membrane is made of a phospholipid bilayer which allows certain molecules in and out of the cell We will discuss 2 basic mechanisms of transport: 1. DIFFUSION 2. OSMOSIS • 2

Diffusion of liquids 3

Diffusion is the net movement of molecules from a region of their high concentration to a region of their lower concentration. The molecules move down a concentration gradient. Molecules continue until they reach equilibrium. 4

DIFFUSION Diffusion is a PASSIVE process which means no energy is used to make the molecules move, they have a natural kinetic energy. AS Biology, Cell membranes and Transport 5

5 Factors that affect diffusion 1. Temperature- Higher temperature diffuse faster 2. Surface area- greater surface area diffuse faster 3. Concentration gradient- Higher gradient diffuse faster 4. Size of particles- Smaller particles diffuse faster 5. Diffusion Medium- Solid slowest Liquid faster Gas fastest 6

Diffusion through a membrane Cell membrane Inside cell Outside cell AS Biology, Cell membranes and Transport 7

Diffusion through a membrane Cell membrane diffusion Inside cell Outside cell AS Biology, Cell membranes and Transport 8

Diffusion through a membrane Cell membrane Inside cell Outside cell EQUILIBRIUM AS Biology, Cell membranes and Transport 9

Osmosis ‘The diffusion of water from an area of high concentration of water molecules (high water potential) to an area of low concentration of water (low water potential) across a partially permeable membrane. 10

Osmosis DILUTE SOLUTION Sugar molecule CONCENTRATED SOLUTION Cell membrane partially permeable. VERY Low conc. of water molecules. High water potential. VERY High conc. Inside cell of water molecules. High water potential. Outside cell AS Biology, Cell membranes and Transport 11

Osmosis Cell membrane partially permeable. Low conc. of water molecules. High water potential. OSMOSIS High conc. of water molecules. High water potential. Inside cell Outside cell AS Biology, Cell membranes and Transport 12

Osmosis Cell membrane partially permeable. OSMOSIS Inside cell Outside cell EQUILIBRIUM. Equal water concentration on each side. Equal water potential has been reached. There is no net movement of water. AS Biology, Cell membranes and Transport 13