Cell Membrane Fig. 3.6

Phospholipids Prevents movement of water soluble molecules and ions

Cholesterol Strengthens cell membrane

Integral Proteins Form channels to allow molecules or ions to enter or leave the cell

Recognition Proteins Carbohydrate Identify the cell

Peripheral Protein Enzymes

Receptor Proteins Reacts with molecular signals

Transport of Materials across the Cell Membrane

Why a cell needs transport ? for obtaining useful materials, and for eliminating metabolic waste Permeability living cell membrane - selectively permeable visking tubing / dialysis tubing - selectively permeable dead cell membrane - freely permeable cell wall (non-living) - freely permeable

Diffusion or Passive Transport molecules move from high concentration to low concentration area (fluid/dissolved solid molecules)

General direction of water movement low solute concentration high solute concentration low water concentration high water concentration

Factors affecting Rate of Diffusion Size (larger size, slower rate) (steeper gradient, faster rate) Temperature (higher temp, faster rate) Concentration gradient (concentration difference between the two areas) Medium (gas > liquid > solid) Surface area (larger area, faster rate)

Importance of diffusion to living organisms get rid of waste products involve in gaseous exchange during respiration absorb mineral salts in plants absorb digested food in mammals

Osmosis water / solvent molecules move from high water concentration to low water concentration area (high water potential to low water potential area) (low solute concentration to high solute concentration area) through a selectively permeable membrane

Active Transport molecules move from low concentration to high concentration area requires energy & carrier occurs in living cells only also transport from high to low concentration in high rate

Active Transport outside carrier molecule cell membrane substances inside Substances passes through the carrier from outside (low conc.) to inside (high conc.)

Fig. 3.17a

Fig. 3.17b

Cell in a Hyperosmotic Solution 350 Crenate 300

Cell in a Hypoosmotic Solution Swell 250 300 Lyse

Cell in Isosmotic Solution No net movement of water 300 300 0.9% 0.9%