AP Biology
Bellwork:Please add 5 more terms to
your Quizlet set and practice for 10
min.
UNIT EXAM on Wed. Sept 10.
Passive transport- 1) Simple Diffusion
Diffusion is the tendency of molecules of any substance to spread
out in the available space
driven by the intrinsic kinetic energy of molecules.
a substance will diffuse from where it is more concentrated to where
it is less concentrated, i.e. down its concentration gradient.
O2, and CO2; small polar molecules
include ethanol, H2O, and urea.
Passive transport- 2) Facilitated Diffusion
1) Channel proteins -provide corridors allowing a specific molecule
or ion to cross the membrane.
These channel proteins allow fast transport
Water channel proteins -aquaprorins
Channels
Open
Channels that spend
almost all of their time in the
open configuration are called
“leak” channels, or pores
Ions, and H2O
Closed
Channels that spend
almost all of their time in the
closed configuration are called
“gated”
Passive transport- 2) Facilitated Diffusion
2)
Carrier Proteins –
Allows movement without
producing an open corridor
1.Molecules (substrates) actually bind with the carrier
(amino acids, sugars, nucleosides, and other small
molecules)
2. Protein changes in shape (conformational change)
Transport Proteins are like Enzymes
Transport proteins
Specific binding sites
Can become saturated
Can be inhibited
Catalyze a process
Enzymes
3. Osmosis is the passive transport of water
Tonicity describes how the size of a cell would change if it were placed in a
solution
Osmosis is the passive transport of water – it occurs until isotonicity
is reached
Osmosis – passive diffusion of water across a semipermeable
membrane
Fig. 8.11
Cell survival depends on balancing water uptake and
loss
Osmosis is the diffusion of water through a selectively permeable membrane.
Tonicity describes how the size
of a cell would change if it
were placed in the solution
Isotonic – same solute/water
concentrations as inside cells
so cells retain their normal
size and shape
hypertonic
H2O
hypotonic
H2O
Cell survival depends on balancing water uptake and
loss
• Osmoregulation : maintanance of osmotic balance
• Paramecium – protist (contractile vacuole)
• The cells of plants, prokaryotes, fungi, and some protists have cell
walls that contribute to the cell’s water balance.
4. Active transport is the pumping of
solutes against their gradients
• Active transport requires the cell to use its own metabolic energy
(ATP).
• Active transport is against the Concentration Gradient (solutes
move from low concentration to high concentration)
• The sodium-potassium pump actively maintains the gradient of
+
+
sodium (Na ) and potassium ions (K ) across the membrane.
Please follow the link.
http://www.brookscole.com/chemistry_d/templates/st
udent_resources/shared_resources/animations/ion_p
ump/ionpump.html
Chart the Steps
Fill in the science process box with:
THhe steps of __the sodium potassium
pump__________
Chart the steps of the process in the bos.
Write a description of the chart giving the
steps in sequence.
Numbered Heads Together
Each person at the team, NUMBER
off 1,2,3,or 4. Remember your number!
Some ion pumps generate voltage across
membranes
All cells maintain a voltage across their plasma membranes.
The cytoplasm of a cell is negative in charge compared to the
extracellular fluid because of an unequal distribution of cations (+)
and anions (-) on opposite sides of the membrane.
This voltage, the membrane potential, ranges f50 to -200 millivolts.
• The membrane potential acts like a battery.
• The membrane potential favors the passive transport of cations
(+) into the cell and anions (-) out of the cell.
• Two combined forces, collectively called the electrochemical
gradient, drive the diffusion of ions across a membrane:
–a chemical force based in an ion’s concentration gradient
–an electrical force based on the effect of the membrane potential
on the ion’s movement.
Some ion pumps generate voltage across
membranes
• Ions diffuse down their electrochemical gradient.
• Special transport proteins, electrogenic pumps, generate the
voltage gradients across a membrane
• Examples of electrogenic pumps – Na-K pump, proton pump
• Proton pump actively transports
+
H out of the cell.
• Plants, fungi, mitochondria,
chloroplast
• These electrogenic
pumps store energy
that can be used to make ATP.
In cotransport, a membrane protein
couples the transport of two solutes
Exocytosis and Endocytosis transport
large molecules
• Small molecules and water
• Large macromolecules
Transport proteins
Vesicles
• Exocytosis: a transport vesicle budded from the Golgi apparatus is
moved by the cytoskeleton to the plasma membrane.
• Endocytosis - a cell brings in macromolecules and particulate
matter by forming new vesicles from the plasma membrane.
• Endocytosis is a reversal of exocytosis.
• One type of endocytosis is phagocytosis, “cellular eating”.
• In phagocytosis, the cell engulfs a particle by extending
pseudopodia around it and packaging it in a large vacuole.
• The contents of the vacuole are digested when the vacuole fuses
with a lysosome.
Fig. 8.19a
• In pinocytosis, “cellular drinking”, a cell creates a vesicle around a
droplet of extracellular fluid.
Fig. 8.19b
• Receptor-mediated endocytosis is very specific in what substances
are being transported.
• Extracellular substances bind to special receptors, on the
membrane surface, especially near coated pits.
• This triggers the formation of a vesicle
Fig. 8.19c
Please Follow the Link
http://www.sumanasinc.com/webcontent/anisamples/m
olecularbiology/endocytosis.html
Transport:
•
•
•
•
•
•
•
•
•
Simple Diffusion
Facilitated diffusion (carrier and channel proteins)
Osmosis – diffusion of water
Active Transport
Electrogenic pumps
Cotransport
Exocytosis
Endocytosis and Receptor- mediated endocytosis
Phagocytosis and Pinocytosis
Why It’s Important
Come up with 10 reasons why, ‘Active
Transport” is important.
Work as a Team but everyone does a
sheet.
Concept Map
Create a Map of ‘Chapter 7: Membrane Transport’
using the Q-trix question cards.