Chapter 7.3: Moving Materials Into and Out of Cells

Homeostasis = keeping a constant internal environment The cell membrane does this by allowing only certain molecules to go in and out

Traffic Across Membranes Selectively Permeable Membranes – some substances can move through and others cannot Also called, semipermeable membranes Can move through - Hydrophobic, non-polar molecules - Small molecules Can’t move through -Large molecules -hydrophilic, polar molecules - Ions (Na +, Ca +, Cl - )

Concentration: The amount of a substance in a given area. [substance] = mass of substance (g) volume (l) Q: Which side has a higher concentration of red dots? AB A: Side A

Passive Transport Transport of molecules without the use of extra energy. Three types: Diffusion Facilitated diffusion Osmosis Goes from high concentration to low concentration.

Diffusion The movement of molecules from an area of high concentration to an area of low concentration Down(with) the concentration gradient (slope) – energy is not needed to go downhill! High Low

Factors that influence the rate of diffusion include: 1. Temperature: Heat increases kinetic energy and thus diffusion 2. Steepness of concentration gradient: 50:1 > 2:1 3. Particle Size: Small molecules diffuse at a quicker rate than larger molecules.

The net movement of molecules will continue until an equilibrium is reached between the two areas net movement Once equilibrium is reached, molecules continue to diffuse across the membrane in both directions but at equal rates. Equilibrium

Facilitated Diffusion Molecules are too big to squeeze through the membrane. Channel proteins act like tunnels to let the molecules through. Goes with (down) the concentration gradient. Q: Is extra energy needed for facilitated diffusion? Why or why not?

Osmosis is an Example of Facilitated Diffusion The diffusion of water. Water always flows from high water concentration to low water concentration. Requires the use of aquaporins (special channel proteins for the movement of water)

Tonicity: The Effects of Osmosis on Cells Solvent: the liquid you dissolve a substance into. ie: water Solute: the substance dissolved in the solvent. ie: salt

Water will tend to go from an area of low solute concentration to an area of high solute concentration

Isotonic: when the concentration of solutes on either side of the membrane are equal - cells do not change Hypotonic: when the solution outside the cell has a lower solute concentration in relation to inside the cell - cells tend to swell and burst Hypertonic: when the solution outside the cell has a higher solute concentration in relation to inside the cell - cells tend to shrink

2M NaCl a) b) c) 1M NaCl 2M NaCl 1M NaCl

Hypotonic Isotonic Hypertonic

Active Transport Movement across a membrane that DOES require energy Different types of Active Transport include: Sodium-Potassium pump Endocytosis Exocytosis Q: From which molecule does the cell get this energy? How?

Molecules move from an area of low concentration to an area of high concentration Go against (up) the concentration gradient High Low

Sodium-Potasium Pump Protein Pumps: sodium (Na+) in and potassium (K+) out. Potassium Sodium Q: Why does this pump require energy to work?

Bulk Transport Endocytosis: transport of larger molecules into the cell Phagocytosis: “cell eating” solid materials are taken into the cell Pinocytosis: “cell drinking” liquid materials are taken into the cell Exocytosis: transport of larger molecules out of the cell.