L.E. Bio Unit 3 Movements Through Cell Membranes 1.Passive Transport 2.Active Transport

Concentration Gradient Starch molecules are too large to pass through the pores in the membrane. Iodine molecules move in both directions, but their net movement is from the bag (high concentration), into the beaker, (low concentration). Iodine combines with starch to form a purplish-colored compound. The net movement of water is into the beaker.

The Concentration Gradient High Concentration Low Concentration Passive Transport Active Transport No Energy Required Osmosis, Diffusion. Facilitated diffusion The steeper the gradient the faster it flows! Concentration Gradient Requires Energy Pumping Pinocytosis and Pagocytosis The steeper the gradient the more energy needed!

PASSIVE TRANSPORT no energy is required for the molecules to move into or out of the cell. From High to Low Concentration. Examples 1.Diffusion 2.Osmosis 3.“facilitated” diffusion. large molecules "helped" across the plasma membrane by carrier proteins

Diffusion Passive-No ATP High  Low – Concentration Equilibrium Example:

Facilitated Diffusion Passive High  Low Uses a carrier protein molecule in the cell membrane

Osmosis Passive High  Low Diffusion of water through a selectively- permeable membrane

Osmosis depends on the relative concentration of solute molecules on either side of the membrane. The presence or absence of cell walls influences how cells respond to osmotic fluctuations in their environment. RBC placed into salt solution, then immediately into distilled water.

Filtration Forces molecules through membranes Occurs by sheer force Example: blood pressure

Isotonic Solution Same water concentration as inside the cell Water will move back and forth, but no net movement.

Hypertonic Solution MUCH (hyper) solute (low water) More water inside the cell than outside Net movement of water OUT of the cell Cell shrinks!!

Hypotonic Solution LITTLE (hypo) solute (high water) More water outside the cell than inside Net movement of water INTO the cell Cell swells!!

Cells in Hypotonic solutions Water diffuses into cell and it swells

Low  High concentration Against the concentration gradient Requires cellular energy (ATP)

Endocytosis – Active Transport Cell takes in large particles by engulfing them Three Examples 1.Pinocytosis–“cell drinking” 2.Phagocytosis – “cell eating” 3.Receptor-mediated endocytosis – cell membrane binds to molecules first before bringing them in

Sodium Potassium Pump - the cell pumps out 3 sodium ions and takes in 2 potassium ions.

Exocytosis