Download BI 103: Leaves Learning Objectives

BI 103: Leaves
An examination of leaves
Chapter 43 cont.
Learning Objectives
• What is the function of the plant leaf?
• How are specific cells and tissues
adapted in the leaf in order to help it
function?
• What do plants need to
photosynthesize?
• How are tissues in the leaf different
from the roots & stem?
• What are examples of specialized
leaves?
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Plant Anatomy: Vegetative Organs
Leaves:
Stem:
Photosynthesis
Gas exchange
Light absorption
Support
Transport
Storage
Roots:
Anchorage
Storage
Transport
Absorption
Form = Function
Introduction
• Other functions of leaves:
– Wastes from metabolic processes
accumulate in leaves and are disposed of
when leaves are shed.
– Play major role in movement of water
absorbed by roots
• Transpiration occurs when water evaporates
from leaf surface.
• Guttation - Root pressure forces water out
hydathodes at tips of leaf veins in some plants.
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Adapted for Photosynthesis
• Leaves are usually thin
– High surface area-to-volume
ratio
– Promotes diffusion of gases
• Leaves are arranged to
capture sunlight
– Are held perpendicular to rays
of sun
– Arranged so they don’t shade
one another
Common Leaf Forms
DICOT
MONOCOT
petiole
axillary
bud
blade
node
blade
sheath
node
3
leaf blade
Leaf Vein
(one vascular
bundle)
leaf vein
cuticle
Upper
Epidermis
Palisade
Mesophyll
stem
xylem
Spongy
Mesophyll
Water, dissolved
mineral ions from
roots and stems
move into leaf
vein (blue arrow)
Lower
Epidermis
50m
phloem
Photosynthetic
products (pink
arrow) enter
vein, will be
transported
throughout
plant body
cuticle-coated cell
of lower epidermis
one stoma (opening
across epidermia)
Oxygen and
water vapor
diffuse out
of leaf at
stomata.
Carbon
dioxide in
outside air
enters leaf at
stomata.
Fig. 29-14, p.501
Epidermis: Cuticle
• Waxy cuticle secreted by epidermis cells
• Protective layer against disease
• Reduced water loss from cells
4
Dermal tissue
• Epidermis - Single layer of cells
covering the entire surface of the leaf
– Devoid of chloroplasts
– Coated with cuticle
– Functions to protect tissues inside
leaves
– Waste materials may accumulate in
epidermal cells.
– Different types of glands may also be
present in the epidermis.
Guard Cells
5
Vascular plants: have stomata
bordered by 2 guard cells
Open when water is abundant.
Close when water is scarce.
Bryophytes: pores
• Bryophytes like moss and
liverworts lack stomata
• Have pores that are always open
Cross section of liverwort thallus
(Conocephalum)
6
Epidermis: Trichomes
Trichomes on an Arabidopsis leaf. Trichomes are
extensions from the plant's epidermis and they occur in
numerous shapes and sizes in various plants.
Trichomes may provide defense against insects
Trichomes
Glandular trichome of Stinging Nettle Urtica
dioica
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Epidermal tissue: Prickles
Prickles: epidermal
cells- larger tichomes
Examples: Rosa spp.
Mesophyll
Most photosynthesis takes
place in the mesophyll between the
two epidermal layers.
I. Palisade Mesophyll
–
Compactly stacked,
barrel-shaped
parenchyma cells,
commonly in two rows
–
Contains most of leaf’s
chloroplasts
II. Spongy Mesophyll
–
Loosely arranged
parenchyma cells with
abundant air spaces
8
Photosynthesis: The Components
?
?
What are the inputs?
?
What are the outputs?
?
?
9
Photosynthesis: The Components
6CO2 + 6H2O + Light energy  C6H12O6 + 6O2
What are the inputs?
- light
- water
- carbon dioxide
What are the outputs?
- glucose
- oxygen
Light is a wave of energy:
colors are different
wavelengths
10
Photosynthesis: Input - Light
The color you see
Intensity
Energy (wavelength)
absorbed
Photosynthesis: Light Absorption
Plants are green because…
• Reflect green light.
• Absorb red, blue
and purple light.
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Photosynthesis: Light Absorption
Plant pigments absorb light….
Absorb red, blue
and purple light
Reflect green light
Leaf Veins: Vascular Bundles
• Xylem and phloem; often
strengthened with fibers
• In dicots, veins are netlike
• In monocots, they are parallel
12
Specialized Leaves
Carnivorous leaves
• Grow in swampy areas
and bogs
• Nitrogen and other
elements are deficient in
soil.
• Specialized leaves trap
and digest insects.
– Pitcher Plants
• Insects trapped and
digested inside coneshaped leaves.
Pitcher plant
Specialized Leaves: Carnivorous
Sundews
• Have round to oval leaves
covered with glandular
hairs that have a sticky
fluid of digestive enzymes
at tip
Sundew
Venus’s Flytraps
• Only in North Carolina and
South Carolina
• Blade halves trap insects.
Venus’s
Flytraps
13
Specialized Leaves
• Floral Leaves (bracts)
– At bases of flowers or flower stalks
– Poinsettia - Flowers do not have petals, instead
brightly colored bracts surround flowers.
– Clary’s sage - Colorful bracts are at top of
flowering stalks above flowers.
Poinsettia
Clary’s sage
Specialized Leaves: Bracts
Example: Flowering dogwood, Cornus nutallii
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Specialized Leaves
• Leaves of Arid Regions
– Arid regions have limited availability of water,
– wide temperature ranges, and high light
intensities.
– Leaves reduce loss of water by:
•
•
•
•
Thick, leathery leaves
Fewer stomata or sunken stomata
Succulent, water-retaining leaves, or no leaves
Dense, hairy coverings
Specialized Leaves
• Leaves of Arid Regions
– Conifers
– Sunken stomata
Tsuga canadensis
Picea
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Specialized Leaves
• Leaves of Aquatic Areas
– Less xylem and phloem
– Mesophyll not differentiated into palisade and spongy
layers.
– Large air spaces
Water lily leaf
Elodea leaf
Specialized Leaves
Tendrils
Tendrils
Spines
Thorn
Thorns - Modified stems
arising in the axils of
leaves of woody plants
Spine
16
Autumnal Changes in Leaf Color
• Chloroplasts of mature leaves contain
several groups of pigments:
– Chlorophylls - Green
– Carotenoids - Yellows
– In fall, chlorophylls break down and other
colors are revealed.
• Water soluble anthocyanins (red or blue)
and betacyanins (red) may also be present
in the vacuole.
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