AP Biology
 The
selectively permeable plasma membrane is
composed of phospholipids and protein, which
allow for its unique functions.
 A) DESCRIBE the structure and properties of
phospholipids and EXPLAIN the important
roles of phospholipids in the plasma
membrane.
 B) EXPLAIN why proteins are an important
component of the cell membrane, based on
their structure and properties.
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 Read
lab packet
 Highlight all vocabulary in background
section
 Read procedures
 Complete #1 on page 15.
 TODAY: Part A
 Procedures on page 6
 Table 1 on page 12
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Time
Start
30 minutes
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Color
Bag
Beaker
clear
amber
Glucose
Bag
Beaker
+
-
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CLASS DATA FOR % CHANGE IN MASS
Water
0.2 M
0.4 M
0.6 M
0.8 M
1.0 M
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 #2:
Iodine diffused into the bag (blue/black);
Glucose diffused out of the bag into the
environment; Osmosis was also occurring bc
it went into the bag as glucose diffused out
 #3: Yes, iodine and glucose diffused, but the
starch could not diffuse bc it was too big
 #4: Osmosis occurred which caused a net
flow of water into the bag increasing its
mass; More water because the environment
was hypotonic (less solute). Equilibrium was
reached.
 #5: Hypotonic because it had less solute than
the bags
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CLASS DATA FOR % CHANGE IN MASS OF POTATOES
Water
0.2 M
0.4 M
0.6 M
0.8 M
1.0 M
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class average
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https://www.youtube.com/watch?v=4JyT__Dea8Q
• Plant cells losing water in hypertonic
solutions
• Shrinking
• Cell membrane pulls away from outer
cell wall
• Very rare
• Opposite?
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 Movement
of a substance across a
membrane with no energy investment
 Direction depends on concentration
 High concentrations to low concentrations
 DOWN or WITH its concentration gradient
 Types: diffusion, osmosis, facilitated
diffusion
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 Movement
from high to low concentrations
 2nd Law of Thermodynamics
governs biological systems
 universe tends towards disorder (entropy)
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movement of water
diffusion
osmosis
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 Water
is very important to life,
so we talk about water separately
 Diffusion of water from
high concentration of water to
low concentration of water

across a
semi-permeable
membrane
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 Direction
of osmosis is determined by comparing
total solute concentrations

Hypertonic - more solute, less water

Hypotonic - less solute, more water

Isotonic - equal solute, equal water
water
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hypotonic
hypertonic
net movement of water
 Cell
survival depends on balancing water uptake
andloss
freshwater
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balanced
saltwater
.05 M
.03 M
Cell (compared to beaker)  hypertonic or hypotonic
Beaker (compared to cell)  hypertonic or hypotonic
Which way does the water flow?  in or out of cell
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 Isotonic

animal cell immersed in
mild salt solution


example:
blood cells in blood plasma
problem: none

no net movement of water

flows across membrane equally, in
both directions

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volume of cell is stable
balanced
 Hypotonic

a cell in fresh water


example: Paramecium
problem: gains water,
swells & can burst


ATP

solution: contractile vacuole

pumps water out of cell

ATP
plant cells

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water continually enters
Paramecium cell
turgid
freshwater
 Contractile
ATP
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vacuole in Paramecium
 Hypertonic

a cell in salt water




plant cells

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example: shellfish
problem: lose water & die
solution: take up water or pump out
salt
plasmolysis = wilt
saltwater
1991 | 2003
 Water

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moves rapidly into & out of cells
evidence that there were water channels
Peter Agre
Roderick MacKinnon
John Hopkins
Rockefeller
 Cell
membrane is the boundary between
inside & outside…

separates cell from its environment
Can it be an impenetrable boundary?
IN
food
carbohydrates,
sugars, proteins
amino acids,
lipids, salts, O2, H2O
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OUT
waste
ammonia
salts
CO2
H2O
products
cell needs materials in & products or waste out
 What
molecules can get through directly?
 fats & other lipids
 What molecules can NOT
inside cell
lipid
salt
NH3
outside cell
sugar aa
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H 2O
get through directly?
 polar molecules
 H2 O
 ions
 salts, ammonia
 large molecules
 starches, proteins
 Membrane
becomes semi-permeable
with protein channels
 specific channels allow specific
material across cell membrane
inside cell
NH
AP
Biology
3
salt
H 2O
aa
sugar
outside cell
 Diffusion
through protein channels
 channels move specific molecules across
cell membrane
 no energy needed
facilitated = with help
open channel = fast transport
high
low
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“The Bouncer”
 Cells
may need to move molecules against
concentration gradient



shape change transports solute from
one side of membrane to other
protein “pump”
conformational change
“costs” energy = ATP
low
ATP
high
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“The Doorman”
Many
models & mechanisms
ATP
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ATP
antiport
symport
 Passive

Transport
Simple diffusion

diffusion of nonpolar, hydrophobic molecules
lipids
 high  low concentration gradient


Facilitated transport



diffusion of polar, hydrophilic molecules
through a protein channel
high  low concentration gradient
 Active

diffusion against concentration gradient



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transport
low  high
uses a protein pump
requires ATP
ATP
simple
diffusion
facilitated
diffusion
active
transport
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ATP
 Moving


through vesicles & vacuoles
endocytosis



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large molecules into & out of cell
phagocytosis = “cellular eating”
pinocytosis = “cellular drinking”
exocytosis
exocytosis
phagocytosis
fuse with
lysosome for
digestion
pinocytosis
non-specific
process
receptor-mediated
endocytosis
triggered by
molecular
signal
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2007-2008
Any Questions??
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