CHAPTER 5? The Working Cell

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CHAPTER 5? The Working Cell
5.3-passive transport is diffusion across a
membrane with no energy cost I. Diffusion A.
Intro 1. In addition to chemical signals,
cells transport H2O, food, and ions across
membrane a. Ion? charged particle B.
Diffusion 1. The mixing of 2 substances by the
random motion of molecules 2. Molecules will
always diffuse from and area of high to an
area of low
5.4-Osmosis is diffusion of water across a
membrane C. Osmosis Diffusion of H2O 1. The
diffusion of H2O across a selectively permeable
membrane 2. Again from an area of high to
an area of low 3. Requires no energy by
the cell a. Water moves freely across membrane
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5.5-Water balance between cells and their
surroundings is crucial to organisms I.
Controlling osmosis A. gradient 1. The
difference in the of particles that occurs
across a selectively permeable membrane 2.
Remember that water moves from high to low
3. Moving with or down the gradient a.
Particles moving from high to low 4.
Moving against or up the gradient a.
Particles moving from low to high
B. Isotonic solution 1. of particles is
equal on both sides of the membrane 2. Cells
in an isotonic solution do not experience osmosis
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C. Hypotonic solution 1. of particles
outside the cell is lower than inside the
cell a. More water outside the cell than
inside 2. Water moves inside the cell causing
the cell to swell a. If solution is to
hypotonic cell will burst
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D. Hypertonic solution 1. of particles
outside the cell is higher than inside the
cell a. More water inside the cell than
outside 2. Water leaves the cell causing it to
shrink
E. Osmotic pressure 1. The pressure that
results from the force of water pushing against
the plasma membrane 2. Also called turgor
pressure
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5.6-Transport proteins may facilitate diffusion
across membranes I. Selective transport A.
Review 1. Not all substances can pass freely
across plasma membrane like water
B. Intro 1. Protein channels and pumps a.
Channels 1. Passageways across plasma
membrane 2. Allows only certain molecules to
cross membrane depending on shape of molecule
b. Pumps 1. Passageways across plasma
membrane that requires a certain amount of
energy 2. Used to pump a molecules against
or up the gradient
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C. Facilitated diffusion 1. free of
charge a. Costs the cell no energy to
perform 2. If molecule can fit through the
protein channel it may enter or leave the
cell 3. Movement occurs due to diffusion,
hence the name a. high to low
4. Called facilitated because channels assist,
or facilitate the diffusion of molecule
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5.8-Cells expend energy in the active transport
of a solute against its gradient I. Active
transport A. comes at a price 1. Energy
must be used to perform B. Allows molecules to
move in only one direction 1. Like a turnstile
in a stadium C. Allows cells to stockpile
certain substances at higher inside the cell
than outside
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D. Sodium-potassium pump (Na, K)
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1. Moves Na out of cell and K into the cell 2.
Na fits into protein receptors inside the
cell 3. Once energy is provided Na is pumped
out of the cell a. once released outside Na
cannot reenter through this channel 4. Once Na
is released K attaches to same protein receptor
outside the cell 5. Na reenters the cell by
facilitated diffusion once is low enough
inside the cell a. K does the same in the
opposite direction
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6. So what is the point of all this? a. One
mechanism used by cells to maintain
homeostasis b. The flow of Na and K is vital
for restoring the balance that is needed for
nerve cells to function
5.9-Exocytosis endocytosis transport large
molecules across membranes I. Moving large
molecules A. Some particles are to large to
fit through any protein channels
B. Endocytosis 1. The process of bringing
molecules into a cell using extensions of the
cell membrane
C. Exocytosis 1. Molecules w/in a sac inside
the cell are discharged from the cell in an
opposite manner to endocytosis
D. Both endocytosis and exocytosis require
energy