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Cell Barriers and Transport
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Chapter 7
Cellular Structure and Function
7.3 The Plasma Membrane
Plasma (Cell) Membrane
 Thin, flexible boundary between the
cell and its environment
 Allows nutrients into the cell
 Allows waste to leave the cell
Chapter 7
Cellular Structure and Function
7.3 The Plasma Membrane
Selective Permeability
 Some things can go through, while others cannot.
The plasma membrane, with its embedded
molecules, controls this.
Chapter 7
Cellular Structure and Function
7.3 The Plasma Membrane
 The plasma membrane is composed of the
phospholipid bilayer.
 A phospholipid means:
a hydrophilic phosphate group.
two hydrophobic fatty acid chains
Chapter 7
Cellular Structure and Function
7.3 The Plasma Membrane
Fluid Mosaic Model
 The phospholipid
bilayer allows other
molecules to “float”
in the membrane.
Other Components
 Proteins
 Cholesterol
 Carbohydrates
Chapter 7
Cellular Structure and Function
7.3 The Plasma Membrane
Proteins
 Transmit signals inside the cell
 Act as a support structure
 Provide pathways for larger substances to enter
and leave the cell
Chapter 7
Cellular Structure and Function
7.3 The Plasma Membrane
Cholesterol
 Prevents fatty acid tails from sticking
together
Chapter 7
Cellular Structure and Function
7.3 The Plasma Membrane
Carbohydrates
 Attached to embedded proteins
 Identify chemical signals
Chapter 7
Cellular Structure and Function
7.3 Cellular Transport: Passive Transport
Passive Transport
 Movement of particles from an area of high
concentration to low concentration without
using energy
Three Modes of Passive Transport
 Diffusion
 Facilitated Diffusion
 Osmosis
Chapter 7
Cellular Structure and Function
7.3 Cellular Transport: Passive Transport
Diffusion
 Movement of particles from an area of high
concentration to an area of lower
concentration
Diffusion
Initial Conditions
Low
High
High
Low
Chapter 7
Cellular Structure and Function
7.3 Cellular Transport: Passive Transport
 Diffusion is controlled by
 Temperature
 Pressure
 Concentration
Dynamic Equilibrium
 When diffusion of material into the cell
equals diffusion of material out of the cell
Chapter 7
Cellular Structure and Function
7.3 Cellular Transport: Passive Transport
Diffusion in a Cell
Chapter 7
Cellular Structure and Function
7.3 Cellular Transport: Passive Transport
Facilitated Diffusion
 Movement of materials across the plasma
membrane using proteins
 https://www.youtube.com/watch?v=IX-kLh34KcQ
Aquaporins – protein channels that allow
water to flow across the cell membrane
Chapter 7
Cellular Structure and Function
7.3 Cellular Transport: Passive Transport
Two types of transport proteins:
Channel Proteins
Carrier Proteins
Chapter 7
Cellular Structure and Function
7.3 Cellular Transport: Passive Transport
Osmosis
 Diffusion of water across a selectively
permeable membrane
Three Types of Solutions
• Isotonic
• Hypotonic
• hypertonic
Chapter 7
Cellular Structure and Function
7.3 Cellular Transport: Passive Transport
Isotonic Solution
 Water and dissolved substances diffuse
into and out of the cell at the same rate.
Plant Cell
Blood Cell
11,397x
Chapter 7
Cellular Structure and Function
7.3 Cellular Transport: Passive Transport
Hypotonic Solution
 Solute concentration is higher inside the cell.
 Water diffuses into the cell.
 BLOWS UP the cell.
Plant Cell
Blood Cell
13,000x
Chapter 7
Cellular Structure and Function
7.3 Cellular Transport: Passive Transport
Hypertonic Solution
 Solute concentration is higher outside the cell.
 Water diffuses out of the cell.
 SHRINKS the cell.
Plant Cell
Blood Cell
13,000x
7.3 Cellular Transport: Passive Transport
Plant cells in a
hypertonic
solution will
plasmolyze.
Plasmolysis:
when the cell
membrane
peels off of the
cell wall and the
vacuole
collapses when
placed in a
hypertonic
environment
http://ctle.hccs.edu/biologylabs/GB1/04Diffusion/04DiffusionIndex.html
Chapter 7
Cellular Structure and Function
7.3 Cellular Transport: Active Transport
Active Transport
 Movement of particles across the cell
membrane using energy
 Three kinds:
 Molecular transport
 Endocytosis
 Exocytosis
Chapter 7
Cellular Structure and Function
7.3 Cellular Transport: Active
Molecular Transport
Active Transport Using Carrier Proteins
• Usually used to transport molecules
against the concentration gradient
Sodium-potassium pump
http://highered.mheducation.com/sites/0072495855/student_view0/chapte
r2/animation__how_the_sodium_potassium_pump_works.html
Cellular Structure and Function
7.3 Cellular Transport: Active
Endocytosis
 Process by which the
cell surrounds and
takes particles into the
cell;
 two types:
 Phagocytosis
 Taking in large quantities


https://www.youtube.com/watch?v=aWItglvTi
Lc
https://www.youtube.com/watch?v=Z_mXDv
ZQ6dU
 Pinocytosis
 Smaller quantities; more
like taking little “sips”, or a
“pinch”.
7.3 Cellular transport: Active
Exocytosis
• Secretion of material out of the plasma
membrane
– Waste vescicle fuses with cell membrane and releases particles
– https://www.youtube.com/watch?v=U9pvm_4-bHg
7.3 Cellular Transport
• What about plants? How do they
“exocytose”?
• They don’t.
• Wastes and toxins get stored in
their vacuoles.
• What about food coming in?
• They make their own, of course!
• Is the cell wall selectively
permeable?
• No. Substances pass easily
through rigid holes in the cell
walls.
7.4 Cell Specialization
• What types of organisms
have specialized cells?
• Multicellular ones
• What are the levels of cellular
organization?
• Cells; similar cells work
together to form…
• Tissues; different tissues
work together to form…
• Organs; organs work together
to form…
• Organ systems, which work
together to form…
• An organism!