Cell Transport EQ: Explain how active and passive transport help the cell maintain homeostasis. SC B-2.5 Explain how active, passive, and facilitated transport serve to maintain homeostasis of the cell

CELL TRANSPORT CHAPTER 7 SECTION 3 DEFINITIONS: Equilibrium: state that exists when the concentration of a substance is the same throughout a space Concentration Gradient: difference in the concentration of a substance across a distance

Passive Transport Diffusion Facilitated Diffusion Osmosis dfn: movement of substances across a cell membrane without requiring energy expenditure by the cell Types: Diffusion Facilitated Diffusion Osmosis

Passive transport Particles are said to move “down their concentration gradient” It is free!

DIFFUSION The movement of particles from regions of higher density to regions of lower density Also called simple diffusion Small, nonpolar molecules pass through the cell membrane by simple diffusion Ex: oxygen, carbon dioxide

SIMPLE DIFFUSION

DIFFUSION RATE Rate of diffusion affected by: Temperature Surface area Concentration gradient Size of molecule

SIMPLE DIFFUSION ACROSS a MEMBRANE

FACILITATED DIFFUSION Same as simple diffusion (particles move down their concentration gradient) except particles require the use of a transport protein to cross cell membrane

FACILITATED DIFFUSION Because it requires a transport protein there is an upper limit to the # of molecules that can enter/exit a cell at any given moment (called Tmax)

Facilitated Diffusion Glucose enters cells via facilitated diffusion

OSMOSIS Osmosis : the diffusion of water from a more dilute solution  a more concentrated solution through a membrane that is permeable to water but not to the solute solute: what is dissolved in solvent solvent: what dissolves the solute

Osmosis Allows cells to maintain water balance as their environment changes http://www.stolaf.edu/people/giannini/flashanimat/transport/osmosis.swf

Osmosis In humans used by: Respiratory system Reproductive system Water Channels (called aquapores) in membrane to allow polar water molecules to enter/exit cell In humans used by: Respiratory system Reproductive system Urinary system (water conservation) Digestive system Homeostasis of body temperature

Osmosis in Red Blood Cells Hypertonic Solutions Concentration of solutes higher than that in cytoplasm Water follows its concentration gradient and moves from ______________ to ___________ Cells will _________________, called crenation http://www.tvdsb.on.ca/WESTMIN/science/sbi3a1/cells/Osmosis.htm

Osmosis in Red Blood Cells If the solution is hypotonic, there is a lower solute concentration outside the cell than inside the cell Water will move _____________ The cell will __________, called hemolysis.

Osmosis with Red Blood Cells If the solution the red blood cell is in has the same concentration of water as the cytoplasm in the cell there will be _________ movement of water. This is called an isotonic solution.

Osmosis in Plant Cells

PASSIVE TRANSPORT http://www.northland.cc.mn.us/biology/Biology1111/animations/transport1.html

ACTIVE TRANSPORT Dfn: the movement of substances against their concentration gradient (against the flow) Substances are moving from an area of lower concentration to an area of higher concentration This requires the cell to use energy (ATP)

ACTIVE TRANSPORT TWO TYPES: PUMPS VESICLES ENDOCYTOSIS EXOCYTOSIS

ACTIVE TRANSPORT PUMPS Use a carrier protein (like facilitated diffusion) but requires expenditure of energy Most common pump: Na+/K+/ATP pump

Na+/K+/ATP pump A carrier protein that uses ATP (1) to actively transport sodium ions (3) out of the cell and potassium ions (2) into the cell. This pump keeps the [Na+] inside the cell lower so that osmosis will not cause the cell to swell with water.

ACTIVE TRANSPORT VESICLES Used to transport molecules that are too large to fit thru a carrier protein. Endocytosis Cell “eating” (phagocytosis) or cell “drinking” (pinocytosis) Cell wraps membrane around material forming vesicle which is taken into cell Exocytosis For moving material out of cell Vesicle fuses with cell membrane releasing contents outside of cell

ENDOCYTOSIS EXOCYTOSIS

Endocytosis Exocytosis

Active Transport Animation http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/ion_pump/ionpump.html

Review Time http://www.learnerstv.com/animation/animation.php?ani=164&cat=biology