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BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 5
The Working Cell
Modules 5.10 – 5.21
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
CELL MEMBRANE STRUCTURE AND FUNCTION
• Cell membranes controls entry and exit of
materials into the cell
• Membranes are selectively permeable or
semipermeable (some substances can pass
throught it, while others cannot).


Cytoplasm
Figure 5.10
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The cell membrane has 2 major
components:
1. A double layer of phospholipids
(lipid bilayer)
2. Protein molecules that serve
as channels, pumps or receptors
for communication.
Your teacher will draw this on the board for
you to copy.
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Draw this diagram of the
cell membrane:
Hydrophobic
↵tails fatty acid
↵Phosphate Head
phospholipid
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5.11 Membrane phospholipids form a bilayer
• Phospholipids are
the main
structural
components of
membranes
Head
• They each have a
hydrophilic head
and two
hydrophobic tails
Symbol
Tails
Figure 5.11A
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• In water, phospholipids form a stable bilayer
– The heads face outward and the tails face
inward
Water
Hydrophilic
heads
Hydrophobic
tails
Water
Figure 5.11B
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• The plasma membrane of an animal cell
Glycoprotein
Carbohydrate
(of
glycoprotein)
Fibers of the
extracellular
matrix
Glycolipid
Phospholipid
Cholesterol
Microfilaments
of the
cytoskeleton
Proteins
CYTOPLASM
Figure 5.12
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5.13 Proteins make the membrane a mosaic of
function
• Proteins that serve as channels
• Others transport substances across the
membrane
Figure 5.13
Transport
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Cell membrane structure
http://www.wisconline.com/objects/index_tj.asp?obj
id=AP1101
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STOP for demonstration
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Your cells can move some substances across
their membranes using NO ENERGY!
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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Background Information on Diffusion
- Diffusion is a process where
molecules move from a region of
higher concentration to a region of
lower concentration.
- The difference in concentration on
either side of a membrane is known
as a concentration gradient.
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Background Information on Diffusion
- Diffusion of water molecules
across a membrane is known as
osmosis.
- Diffusion will occur until an
equilibrium is reached. (some
will move each direction in equal
amounts)
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5.14 Passive transport is diffusion across a
membrane
• In passive transport,
substances diffuse
through membranes
without work by the
cell
Molecule
of dye
– They spread from
areas of high
concentration to
areas of lower
concentration
EQUILIBRIUM
EQUILIBRIUM
Figure 5.14A & B
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Membrane
• Many membrane proteins are enzymes
• Some proteins function as receptors for
chemical messages from other cells
– The binding of a messenger to a receptor may
trigger signal transduction
Messenger molecule
Receptor
Activated
molecule
Figure 5.13
Enzyme activity
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Signal transduction
Transport Across the Cell Membrane
The cell uses 2 types of transport:
1. Passive transport
- Passive transport requires
NO ENERGY use by
the cell. Substances move
along a concentration
gradient.
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1. Passive transport continued…
a. Molecules may be moved
through a process called
simple diffusion.
- Examples: Water, oxygen,
carbon dioxide, lipid soluble
molecules
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1. Passive transport continued…
b. Facilitated diffusion
- Uses carrier proteins to
transport molecules that are
not lipid soluble
- Examples: glucose, some
ions – sodium, potassium
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http://programs.northlandcollege.edu/biology/Biol
ogy1111/animations/transport1.html
Link to illustrate passive
transport
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2. Active Transport
- This transport requires the cell
to USE ENERGY
- Examples: large compounds
OR when molecules are moved
against the concentration
gradient.
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2. Active Transport
2 types of Active Transport
a. Protein Pumps – carry
molecules across the
membrane against the
concentration gradient
(moleculer transport) neuron
animation
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2. Active Transport
b. Bulk Transport
- This is where large
amounts of molecules are
carried across. There are
3 types of this.
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2. Active Transport
b. Bulk Transport
1. Endocytosis – cell membrane
brings materials into the cell by
infoldings of the membrane
which can form vacuoles.
2 Forms: Phagocytosis – ameba
undissolved materials
Ex: Ameba eating food
Pinocytosis –
dissolved materials
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– or the membrane may fold inward, trapping
material from the outside (endocytosis)
Figure 5.19B
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• Three kinds of endocytosis
Pseudopod of
amoeba
Food being
ingested
Plasma
membrane
Material bound to
receptor proteins
PIT
Cytoplasm
Figure 5.19C
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2. Active Transport
b. Large quantity Transport
2. Exocytosis – removes material
from the cell through
outpinchings of the cell
membrane. Ex: wastes
3. Contractile Vacuole - Used
for removing excess water from a
cell. Ex: a freshwater
paramecium contractile vacuole
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5.19 Exocytosis and endocytosis transport large
molecules
• To move large molecules or particles through a
membrane
– a vesicle may fuse with the membrane and expel
its contents (exocytosis)
FLUID OUTSIDE CELL
Figure 5.19A
CYTOPLASM
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http://programs.northlandcollege.edu/biology/Biol
ogy1111/animations/transport1.html
Link to illustrate active
transport
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What will happen to a plant or
animal cell when placed in fresh
or salt water?
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Background Information
Hypertonic – Solution that has a higher
concentration of Solute than a
surrounding solution
Hypotonic – Solution that has a lower
concentration of solute than a
surrounding Solution
Isotonic – Two solutions have the
same solute concentrations
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FRESH WATER
Animal Cell
Plant Cell
- water is more highly concentrated
outside the cell
- water will enter the cell
100%
SAME, but
H20
Cell
85%
H20
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plant w/cell
wall
Red blood cell
will explode.
(called
CYTOLYSIS)
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Plant Cell will NOT
explode because the
cell wall prohibits it.
(becomes TURGID)
SALT WATER
Animal cell
Plant Cell
- water is more highly concentrated
inside the cell
- water will exit the cell
80%
SAME, but
plant w/cell
Cell H20
wall
85% 20% salt
H 20
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- Plant cell will lose
-Animal Cell will
water.
lose water and
- The cell membrane wil
shrink (becomes pull away from the cell
CRENATE)
wall – (this is called
PLASMOLYSIS.)
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Red blood cell in isotonic environment
Red blood cell in hypertonic solution
cytolysis and crenation in red blood cells
osmosis
http://www.wisconline.com/objects/index_tj.asp?objid=AP11003
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5.15 Osmosis is the passive transport of water
• In osmosis, water
travels from an
area of lower
solute
concentration to
an area of higher
solute
concentration
Hypotonic
solution
Hypertonic
solution
Selectively
permeable
membrane
Solute
molecule
HYPOTONIC SOLUTION
HYPERTONIC SOLUTION
Water
molecule
Selectively
permeable
membrane
Solute molecule with
cluster of water molecules
NET FLOW OF WATER
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Figure 5.15
5.16 Water balance between cells and their
surroundings is crucial to organisms
• Osmosis causes cells to shrink in a hypertonic
solution and swell in a hypotonic solution
– The control of water balance
(osmoregulation) is essential for organisms
ISOTONIC
SOLUTION
HYPOTONIC
SOLUTION
HYPERTONIC
SOLUTION
(1) Normal
(2) Lysing
(3) Shriveled
ANIMAL
CELL
Plasma
membrane
PLANT
CELL
Figure 5.16
(4) Flaccid
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(5) Turgid
(6) Shriveled
5.17 Transport proteins facilitate diffusion across
membranes
• Small nonpolar molecules diffuse freely through
the phospholipid bilayer
• Many other kinds of molecules pass through
selective protein pores by facilitated diffusion
Solute
molecule
Transport
protein
Figure 5.17
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