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Chapter 7
Lecture Outline
Leaves
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Outline

Introduction
• Leaf Development
• Leaf Parts
• Leaf Complexity
• Leaf Vein & Leaflet Pattern
• Functions of Leaves

Leaf Arrangements and Types

Internal Structure of Leaves

Specialized Leaves

Autumnal Changes in Leaf Color

Human and Ecological Relevance of Leaves
INTRODUCTION

LEAF DEVELOPMENT: All leaves originate as
primordia in buds.

LEAF PARTS (Gross Anatomy) At maturity,
most leaves have:
• Petiole (rachis) = _________________
–
Leaves that are sessile lack a petiole
• Lamina = _______________________
• Veins = ________________________

Leaves of flowering plants at nodes also usually
have axillary buds at base.

LEAF COMPLEXITY
• SIMPLE LEAVES = ___________
• COMPOUND LEAVES = _______

LEAF VEIN & LEAFLET
PATTERN
• PINNATE: ______________
– Simple Pinnate
– Compound Pinnate
o 1st level
o 2nd level
• PALMATE: ______________
– Simple Palmate
– Compound Palmate
Palmately
compound
2nd level
Compound
Pinnate

LEAF VEINATION …
•
PARALLEL:
Parallel
venation

Monocots - Parallel venation

Dicots - Pinnate or Palmate.

FUNCTIONS OF LEAVES =
_______________________________________
• OrganellE: ___________________
• Cell: ___________________
• Need:
–
_________________
–
_________________
–
_________________
• Produce:
• Stomata function.
–
Guard Cells
• Other functions of leaves:
–
Wastes disposed of when leaves shed.
–
Water movement
o Transpiration =__________________.
Leaf Arrangements and Types

Leaves at nodes
–
Opposite
–
Alternate
–
Whorled
Alternate
Opposite
Whorled
INTERNAL STRUCTURE OF LEAVES

3 regions: Epidermis, Mesophyll, Veins

Epidermis, Herbaceous &
Woody plants
• Surface coated with __________
• Functions: 1)____________
2) Water:___________________
3) Glands
•
Stomata
Internal Structure of Leaves …
• Stomata
–
Location: ___________
–
Bordered by two _____________ Cells.
o
–
Have a thickened inner wall
Functions: _____________________
« Gas exchange
« Evaporation of water
How Stomata open & close:
• Changes in water content cause them to inflate or deflate.
• Rigid inner surface remains stiff
Inflate - Stomata open
Deflate - Stomata close

MESOPHYLL: Region between upper and lower
epidermis, excluding the veins.
• FUNCTION: __________________________________
• EUDICOTS: TWO SUB-REGIONS
1) Palisade Mesophyll
Location: _____
– Shape of cells:
______________
- # Contains chloroplasts
–
2) Spongy Mesophyll
Location: _______
– Shape of cells: ____________
– Air spaces
NOT IN MONOCOTS
–
Microscopic View of a EUDICOT Mesophyll
MONOCOT Mesophyll
Vein
Chlorencyma
Cells

VEINS (vascular bundles)
• Location: _________________________
• Tissue & Cells: ____________________
–
Surrounded by bundle sheath of thicker-walled
parenchyma
MONOCOT: Zea (Corn) Leaf
Guard Cells
Vein
ZEA VEIN
Companion
Cells
Sieve-Tube
Cells
Eudicot Vein
Vessels
Sieve-Tube
Cells
Companion
Cells

Differences found in Monocots Flowering plants
• Mesophyll noy differentiated into palisade & spongy layers
• Stomata on upper & lower epidermis
• BULLIFORM CELLS
on either side of
main central vein
• Function: Causes leaf
to fold or roll,
reducing transpiration
Monocot leaf cross section
SPECIALIZED LEAVES

Shade Leaves
Shade
• Amount light:
– Overall Size:
_________
– Thickness: ____
– Have fewer hairs
Sun
Sun
leaf
Shade
leaf

LEAVES OF ARID REGIONS
• Problems for plant:
– Water: ________________
– Temperatures: ______________
– Light Intensities: _______________
• Leaves reduce loss of water by:
– Cuticle:
– Thickness:
– # Stomata
o or sunken stomata
– Dense, hairy coverings, often silver

LEAVES OF AQUATIC AREAS
• Less xylem and phloem
• Mesophyll not differentiated into palisade and spongy
layers.
• Large air spaces

TENDRILS
• Shape: __________
• Function: _________
Tendrils
Examples: Garden peas

SPINES
• Shape:
• Function:
Also reduce leaf surface
and water loss,
–
Spine
Cacti
o Leaf tissue replaced with
sclerenchyma.
o Photosynthesis occurs in stems.
Specialized Leaves

Thorns - Modified stems
in axils of woody plants
Thorn

Prickles - Outgrowths
from epidermis or cortex
Prickle

Storage leaves
• Succulent leaves: Store ______________
–
parenchyma cells with large vacuoles
–
Many desert plants
• Fleshy leaves store ____________.
–
Onions, lily

Flower-Pot Leaves
•
urn-like pouches:
• Ants bring soil & Nit.
Wastes:
Flower-pot leaf sliced lengthwise

Window leaves
• Succulent, Africa
• Leaves buried in ground.
–
–
End is transparent
Function:

Reproductive Leaves
• Walking fern - New plants at leaf tips
• Air plant - Tiny plantlets along leaf margins
Air Plant

Floral Leaves (bracts)
• bases of flowers/flower stalks
• Poinsettia - brightly colored bracts surround
flowers.
• Clary’s sage - Colorful bracts are at top of
flowering stalks.
Poinsettia
Clary’s sage

Insect-Trapping Leaves
• swampy areas and bogs
–
Nitrogen is:
o
Specialized leaves trap
and digest insects.
• Pitcher Plants
–
cone-shaped leaves.
Pitcher plant

Insect-Trapping Leaves
• Sundews
–
leaves covered with
glandular hairs have sticky
digestive enzymes
–
Venus’s Flytraps
–
North Carolina and South
Carolina
–
Mechanically trap insects.
Sundew
Venus’s
Flytraps

Insect-Trapping Leaves
• Bladderworts
–
floating in shallow water
–
bladders have trap doors trap insects inside
Bladder of bladderwort
Autumnal Changes in Leaf Color

Chloroplasts and
pigments:
•
Chlorophylls - Green
•
Carotenoids - Yellows
•
In fall, chlorophylls break
down and other colors are revealed.
anthocyanins
(red or blue) and betacyanins
(red) may present in
vacuole.
Human and Ecological Relevance of Leaves

STUDENTS READ ON YOUR OWN IN TEXT
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