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ENERGY-CONVERTING ORGANELLES
4.15 Chloroplasts convert solar energy to chemical
energy
• Chloroplasts are found in plants and some
protists
• Chloroplasts convert solar energy to chemical
energy in sugars
Chloroplast
Stroma
Inner and outer
membranes
Granum
Figure 4.15
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Intermembrane
space
4.16 Mitochondria harvest chemical energy from
food
• Mitochondria carry out cellular respiration
– This process uses the chemical energy in food to
make ATP for cellular work
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MITOCHONDRION
Outer
membrane
Intermembrane
space
Inner
membrane
Cristae
Figure 4.16
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Matrix
THE CYTOSKELETON AND RELATED
STRUCTURES
4.17 The cell’s internal skeleton helps organize its
structure and activities
• A network of protein fibers makes up the
cytoskeleton
Figure 4.17A
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• Microfilaments of actin enable cells to change
shape and move
• Intermediate filaments reinforce the cell and
anchor certain organelles
• Microtubules
– give the cell rigidity
– provide anchors for organelles
– act as tracks for organelle movement
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Actin subunit
Tubulin
subunit
Fibrous subunits
25 nm
7 nm
MICROFILAMENT
10 nm
INTERMEDIATE
FILAMENT
Figure 4.17B
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MICROTUBULE
4.18 Cilia and flagella move when microtubules
bend
• Eukaryotic cilia and flagella are locomotor
appendages that protrude from certain cells
• A cilia or flagellum is composed of a core of
microtubules wrapped in an extension of the
plasma membrane
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FLAGELLUM
Electron micrograph
of sections:
Outer microtubule
doublet
Plasma
membrane
Flagellum
Central
microtubules
Outer microtubule
doublet
Plasma
membrane
Figure 4.18A
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Basal body
Basal body
(structurally identical to centriole)
• Clusters of microtubules drive the whipping
action of these organelles
Microtubule doublet
Dynein arm
Figure 4.18B
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Sliding
force
EUKARYOTIC CELL SURFACES AND
JUNCTIONS
4.19 Cell surfaces protect, support, and join cells
• Cells interact with their environments and each
other via their surfaces
• Plant cells are supported by rigid cell walls
made largely of cellulose
– They connect by plasmodesmata, channels that
allow them to share water, food, and chemical
messages
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Walls of two
adjacent
plant cells
Vacuole
PLASMODESMATA
Layers of one
plant cell wall
Cytoplasm
Plasma membrane
Figure 4.19A
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• Animal cells are embedded in an extracellular
matrix
– It is a sticky layer of glycoproteins
– It binds cells together in tissues
– It can also have protective and supportive
functions
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Tight junctions can bind cells together into
leakproof sheets
• Anchoring
junctions link
animal cells
TIGHT
JUNCTION
ANCHORING
JUNCTION
• Communicating
junctions allow
substances to
flow from cell
to cell
COMMUNICATING
JUNCTION
Plasma
membranes of
adjacent cells
Figure 4.19B
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Extracellular
matrix
4.20 Eukaryotic organelles comprise four
functional categories
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Table 4.20 (continued)
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