Biology, Seventh Edition
Solomon • Berg • Martin
Chapter 32
Leaf Structure and
Function
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Leaves typically consist of
• Broad flat blade
• Stalk-like petiole
• Some also have
• Small stipules (small, leaf-like
outgrowths from the base)
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
Parts of
a leaf
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Leaves may be
• Simple (having a single blade)
• Compound (having a blade
divided into two or more leaflets)
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
Simple, pinnately compound and
palmately compound leaves
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Leaf arrangement on a stem
may be
• Alternate (one leaf at each node)
• Opposite (two leaves at each
node)
• Whorled (three or more leaves at
each node)
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
Leaf arrangement may be
alternate, opposite, or whorled
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Leaves may have
• Parallel venation
• Netted venation
–Pinnately netted (with several major
veins radiating from one point
–Palmately netted (with veins
branching along the entire length of
the midvein
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
Venation patterns include parallel,
pinnately netted, and palmately netted
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Major tissues of the leaf
• Epidermis
• Photosynthetic ground tissue
• Xylem
• Phloem
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Epidermis
• Covers upper and lower surfaces
of the leaf blade
• Coated by a waxy cuticle
enabling plant to survive a
terrestrial existence
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
The thick, waxy cuticle and sunken stomata are two
structural adaptations that enable Pinus to retain its
needles throughout the winter
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Epidermis, cont.
• Has stomata permitting gas
exchange for photosynthesis;
each surrounded by
–Two guard cells, often associated
with subsidiary cells providing a
reservoir of water and ions
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
Tissues in
a typical
leaf blade
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Mesophyll consists of
photosynthetic parenchyma
cells
• Palisade mesophyll (functions
primarily for photosynthesis
• Spongy mesophyll (functions
primarily for gas exchange)
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Leaf veins have
• Xylem (to conduct water and
essential minerals to the leaf)
• Phloem (to conduct sugar
produced by photosynthesis to
the rest of the plant)
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Monocot leaves
• All have parallel venation
• Some do not have mesophyll
differentiated into distinct
palisade and spongy layers
• Some have dumbbell-shaped
guard cells, unlike more common
bean-shaped guard cells
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
Cross section of a monocot leaf
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
Variation in
guard
cells
(a) Guard cells
of dicots and
many
monocots are
bean-shaped
(b) Some
monocot
guard cells
are dumbbellshaped
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Dicot leaves
• All have netted venation
• All have mesophyll differentiated
into distinct palisade and spongy
layers
• All have bean-shaped guard cells
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
Cross section of a dicot leaf
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Photosynthesis and leaf structure
• Broad, flattened leaf blade is
efficient collector of radiant energy
• Stomata open diurnally for gas
exchange and close nocturnally to
conserve water
• Transparent epidermis allows light
into leaf for photosynthesis
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Photosynthesis and leaf
structure, cont.
• Air spaces in mesophyll tissue
permit rapid diffusion of
–CO2 and water into mesophyll cells
–Oxygen out of mesophyll cells
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• With regard to the opening of
stomata, blue light triggers
• Activation of ATP synthase in the
guard cell plasma membrane
• Synthesis of malic acid
• Hydrolysis of starch
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
Mechanism of stomatal opening
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Physiological changes
accompanying stomatal opening
and closing
• When malic acid ionizes, protons
(H+) are produced
• Protons are pumped out of the
guard cells by ATP synthase
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Physiological changes, cont.
• As protons leave guard cells, an
electrochemical gradient forms on
the two sides of the guard cell
plasma membrane
• Electrochemical gradient drives
uptake of potassium ions through
voltage-activated potassium
channels into guard cells
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Physiological changes, cont.
• Chloride ions are also taken into
guard cells through ion channels
• These osmotically active ions
increase the solute concentration
in the guard cell vacuoles
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Physiological changes, cont.
• Resulting osmotive movement of
water into guard cells causes
them to become turgid, forming a
pore
• As the day progresses,
potassium ions slowly leave
guard cells
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
Temporary wilting
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Physiological changes, cont.
• Starch is hydrolyzed to sucrose,
which increases in concentration
in the guard cells
• Stomata close when water leaves
guard cells due to decline in
concentration of sucrose
(osmotically active solute)
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Physiological changes, cont.
• Sucrose is converted to starch
(osmotically inactive)
• Some environmental factors affecting
stomatal opening and closing
–Light or darkness
–CO2 concentration
–Water stress
–Plant’s circadian rhythm
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Transpiration
• Is loss of water vapor from aerial
parts of plants
• Occurs primarily through stomata
• Rate of transpiration affected by
environmental factors, such as
• Temperature
• Wind
• Relative humidity
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Transpiration represents a
trade-off for plants
• Beneficial because of CO2
requirement
• Harmful because of need to
conserve water
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Guttation and transpiration
• Guttation, the release of liquid
water from leaves of some plants,
occurs through special structures
when
–Transpiration is negligible and
–Available soil moisture is high
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
Guttation
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Guttation and transpiration, cont.
• Transpiration
–Is the loss of water vapor
–Occurs primarily through the stomata
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Leaf abscission
• Loss of leaves that often occurs
–With approach of winter (temperate
climates) or
–At beginning of dry period (tropical
climates with wet and dry seasons)
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Leaf abscission, cont.
• Complex process involving
changes occurring prior to leaf fall
–Physiological
–Anatomic
• Abscission zone develops where
petiole detaches from stem
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Leaf abscission, cont.
• From leaves to other plant parts, the
following are transported
–Sugars
–Amino acids
–Many essential minerals
• Chlorophyll breaks down
• Carotenoids and anthocyanins
become evident
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
Abscission
zone
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Examples of modified leaves
• Spines deter herbivores
• Tendrils grasp other structures (to
support weak stems)
• Bud scales protect
–Delicate meristematic tissue
–Dormant buds
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
Leaves of
Mammilaria
are modified
to form spines
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
Leaves of
Echinocystis
lobata are
modified to
form tendrils
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
A terminal bud
and two axillary
buds of an Acer
twig have
overlapping bud
scales to
protect buds
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
• Examples of modified leaves, cont.
• Bulbs are short underground stems
with fleshy leaves specialized for
storage
• Succulent leaves serve for water
storage
• Leaves of insectivorous plants trap
insects
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
The leaves of bulbs such as Allium cepa are
fleshy for storage of food materials and water
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Biology, Seventh Edition
CHAPTER 32 Leaf Structure and Function
The succulent leaves of Senecio rowleyanus
are spherical to minimize surface area, thereby
conserving water
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