Transcript Homeostasis and Transport

Chapter 5: Homeostasis and Transport
5-1 Passive Transport
5-2 Active Transport
5-1 Passive Transport
I. Diffusion (i.e., kinetic NRG of molecules)
• Movement of X from [HIGH] to [LOW].
(1) Passive Transport (e.g., diffusion, osmosis)
• Movement down a gradient, w/o using NRG.
(2) Concentration Gradient (required for diffusion)
• DIFFERENCE in concentration; [HIGH] to [LOW].
(A) Equilibrium (RESULT of diffusion)
• UNIFORM distribution over time.
(B) Diffusion Across Membranes
• TWO conditions:
(1) SIZE?
(2) CHARGE?
Ex: CO2 and O2, are small and easily diffuse through the bilayer.
Critical Thinking
(1) A gelatin block is prepared with a CHEMICAL INDICATOR that turns
PINK in the presence of a BASE. The block is enclosed in a MEMBRANE
and placed in a beaker of AMMONIUM HYDROXIDE solution. After 30
minutes, the block begins to TURN pink. What may have occurred to
PRODUCE this observable result?
II. Osmosis (i.e., diffusion of WATER)
• WATER moves from LOW [OAS] to HIGH [OAS]
NOTE: OAS: Osmotically Active Substance (a solute); salts, sugars, or
proteins.
Critical Thinking
(2) Sea water has a HIGHER concentration of SOLUTES than do human
body cells. Why might drinking large amounts of SEA WATER be
DANGEROUS for the human body’s equilibrium?
(A) Direction of Osmosis (NET direction of water)
• Water moves towards the OAS (where there is LESS water).
(1) Hypotonic ([OAS]CELL > [OAS]SOLUTION )
• Cell SWELLS  WATER into cell FROM solution.
(Ex: Red Blood Cell in dH2O)
(2) Hypertonic ([OAS]SOLUTION > [OAS]CELL)
• Cell SHRINKS  WATER out of cell INTO solution.
(Ex: Red Blood Cell in salt H2O)
(3) Isotonic ([OAS]CELL = [OAS]SOLUTION)
• Cell shape is contant due to EQUAL water into AND out of cell.
(Ex: Red Blood Cell in isotonic H2O)
(B) How Cells DEAL With Osmosis
• Too much salt OR too little salt can be fatal for cells.
(1) Contractile Vacuoles (found in freshwater protists)
• Collects and PUMPS out EXCESS water using NRG.
(i.e., NOT osmosis, pumping AGAINST gradient)
Critical Thinking
(3) Sometimes water SEEPS through the concrete WALL of a basement
after a heavy rain, and the homeowner must REMOVE it with a sump pump.
HOW can this situation be compared to the action of a unicellular organism
that inhabits a freshwater pond?
(2) Turgor Pressure (inside central vacuole of PLANT cells)
• Pressure of water AGAINST a plant CELL WALL due to a HYPOTONIC
surrounding.
Critical Thinking
(4) There is a HIGHER concentration of air molecules INSIDE an inflated
balloon than there is outside the balloon. Because of their constant
random motion, the molecules inside press against the balloon and keep it
taut. How is the pressure exerted by these air molecules SIMILAR to
TURGOR PRESSURE? How might it be DIFFERENT?
(3) Plasmolysis (i.e., plant cell COLLAPSING)
• Turgor pressure is LOST and cell membrane COLLAPSES from plant cell
wall.
(i.e., wilting of plants becoming DEHYDRATED)
(4) Cytolysis (i.e., animal cell BURSTING)
• Cell cannot stop movement of water INTO itself; cell swells and lyses.
(Ex: Red Blood Cells in Hypotonic: Hemolysis)
III. Facilitated Diffusion (e.g., glucose)
• ASSISTED by membrane proteins; “CARRIER proteins.”
Ex: Glucose is TOO LARGE for SIMPLE diffusion through the bilayer.
(1) Carrier Proteins (e.g., integral proteins)
• Move molecules down their gradient WITHOUT use of NRG.
IV. Diffusion Through Ion Channels (usually always OPEN)
• Move IONS across the cell membrane due to their charge.
(1) Ion Channels allow ions to pass through bilayer BUT are specific to
serve only certain ions.
Common ions include…
Na+, K+, Ca+2, and Cl-
• Gated-Ion Channels open AND close in response to 3 types of stimuli:
• Electrical Signals (Nerve Impulses)
• Chemical Signals in the Cytosol
• Chemical Signals in the ECM
5-2 Active Transport
I. Cell Membrane Pumps (SPECIFIC)
• Pump AGAINST concentration gradient (LOW  HI).
(1) Active Transport (NRG required ATP is SPLIT into ADP + PO4)
• (a) Protein Pumps, (b) Endocytosis, (c) Exocytosis.
Critical Thinking
(5) If a cell were exposed to a POISON that blocked the cell’s ability to
manufacture ATP, what EFFECT would that have on the cell membrane’s
TRANSPORT processes?
(A) Sodium-Potassium Pump
• Moves Na+ and K+ ions AGAINST their gradients.
NOTE: To function, cells MUST have a greater [Na+] OUTSIDE cell and a
greater [K+] INSIDE the cell.
Critical Thinking
(6) Some plant cells have carrier proteins that transport SUGAR molecules
and HYDROGEN ions (H+) into the cytosol at the same time. These carrier
proteins move sugar molecules UP their gradient as H+ move DOWN their
gradient. How would the transport of sugar into these cells AFFECT the
pH of the cells’ EXTERNAL environment?
Critical Thinking
(7) During intense exercise, POTASSIUM (K+) tends to accumulate in the
fluid SURROUNDING muscle cells. What membrane protein helps muscle
cells COUNTERACT this tendency? Explain how this works.
II. Endocytosis and Exocytosis
• Used when material is TOO large to fit through a carrier protein.
(A) Endocytosis
• Cells INGEST fluid, macromolecules, and even cells into VESICLES.
(1) Vesicle (membrane-bound)
• BUBBLE pinched off from cell membrane (fuses with a lysosome)
(2) Pinocytosis…
• Endocytosis of FLUIDS from ECM into cell (i.e., cell DRINKING)
(3) Phagocytosis
• Endocytosis of materials OR cells from ECM into cell (i.e., cell eating)
Critical Thinking
(8) When a cell TAKES IN substances through endocytosis, the cell
membrane forms an INSIDE-OUT vesicle. That is, the OUTSIDE of the
cell membrane becomes the INSIDE of the vesicle. What might this
suggest about the STRUCTURE of the cell membrane?
(4) Phagocytes
• Cells ENGULF and ingest cell debris, viruses, and bacteria.
(B) Exocytosis (when a cell releases PROTEINS that it made)
• VESICLES fuse with CELL MEMBRANE and RELEASE contents into ECM.
Extra Slides AND Answers for Critical Thinking Questions
(1) Ammonium hydroxide is small enough to diffuse through the membrane,
and because it’s a base, it turns the indicator pink.
(2) The solutes in sea water would make the solution outside the body cells
more concentrated. Water would then diffuse out of the cells, causing
them to shrink and possibly die.
(3) The organism’s selectively permeable membrane can be compared to the
porous concrete wall; water crosses both barriers. A contractile vacuole
removes water from the organism using energy supplied by the organism,
just as the sump pump removes water using electrical energy.
(4) The air pressure in a balloon resembles the turgor pressure in that
random molecular motion keeps the outer membrane taut. One difference
is that the cell membrane is more permeable to water than the balloon is to
air. Also, there is no cell wall surrounding a balloon to limit the balloon’s
expansion.
(5) All active transport processes would stop, because they require the cell
to expend energy and ATP is the main energy currency of the cell. All
passive transport processes would continue until the concentration
gradient disappeared.
(6) Since hydrogen ions move into the cells along with the sugar molecules,
the transport of sugar into the cells would lower the concentration of
hydrogen ions in the external environment, raising the pH. Removing
hydrogen ions from the external environment would stop the entry of sugar
into the cells by this mechanism.
(7) The sodium-potassium pump counteracts the accumulation of potassium
outside cells by transporting potassium into the cells in exchange for
sodium.
(8) It suggests that the cell membrane’s inner and outer layers have
essentially the same structure and are, therefore, interchangeable.