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
 dfn: movement of substances across a cell membrane
without requiring energy expenditure by the cell
 Types:
 Diffusion
 Facilitated
 Osmosis
Diffusion
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 T )
max
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
 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/i
on_pump/ionpump.html
Review Time
 http://www.learnerstv.com/animation/animation.p
hp?ani=164&cat=biology