Ch 11- Leaves In dicots, the typical foliage leaf consists of: blade

Ch 11- Leaves
In eudicots, the typical foliage leaf consists of:
blade
petiole
Many leaves also have stipules at the base of the petiole.
The axil is where the leaf joins the stem and it forms an angle between the petiole and the stem.
Some leaves lack petioles and are termed sessile.
In monocots, such as lilies and grasses, the leaf expands out in a sheath.
Leaf blade variation
-simple
smooth
toothed
deeply lobed
-compound
There are 2 types of compound leaves:
Pinnately compound leaves:
-leaflets are arranged along
a central axis that is an
extension of the petiole
Palmately compound leaves:
-leaflets arise from a common
point at the end of the petiole
Leaves also possess a wide variety of patterns
of veins which contain xylem and phloem
Monocots
Eudicots
Elm
Parallel
Netted
Pinnately netted veins
alternate
Leaves can be arranged along a stem in a number
of different ways
Norway maple
Palmately netted veins
opposite
whorled
Leaves are complex structures composed of 4 main types of tissues:
-epidermis -tough outer cell layer of the leaf that protects
inner tissues and provides structural support
-mesophyll -main photosynthetic tissue of the leaf
-xylem
-phloem
-conducting tissues which form the vascular bundles
or veins of the leaf
The structure of the leaf is dependent on the plant’s environment
hydrophytes
plants growing in wet environments
xerophytes
plants with leaves adapted to dry environments
mesophytes
plants that require moderately moist environments
Epidermis
Epidermal cells secrete a waxy layer (cuticle) which help retard water loss
Mesophytes
Hydrophytes
Xerophytes
Epidermis
Epidermal cells may be specialized to form hairs called trichomes.
Trichomes serve a variety of functions:
Epidermal tissue typically contains many thousands of
minute pores called stomata (sing. stoma).
When the stomata open, water vapor and oxygen move out of the leaf
and carbon dioxide moves into the interior of the leaf.
Each stoma consists of a pore surrounded by two guard cells.
Mesophyte
Hydrophyte
The upper epidermis of grass leaves has another specialized type of cell- bulliform cell.
When these cells are filled with water (turgid), the leaf is unfolded to capture sunlight.
When bulliform cells are limp (flaccid), the leaf folds up to reduce water loss.
Xerophytes
Mesophyll is located between the upper and lower epidermis
Mesophyll cells are:
The intracellular spaces facilitates gas exchange and is connected to the
external atmosphere by stomata
Mesophyll tissue is organized in 2 layers:
Eudicots
-Distinct palisade
and spongy layers
in eudicot
Monocots
-Mesophyll is not
differentiated into
distinct palisade
and spongy parenchyma
in monocots
-Bundle sheath cells
are also very conspicuous
in monocots
Xylem and phloem are the conducting tissues of leaf veins
Xylem conducts water and dissolved minerals to the leaf tissues
Phloem conducts dissolved sugars from the leaf tissues.
Veins are surrounded by bundle-sheath which are made
up of parenchyma cells.
In some leaves, the bundle-sheath is connected to the
upper and lower epidermis by bundle-sheath extensions.
Plants lose large quantities of water through transpiration
Transpiration is the evaporation of water from plant
surfaces via epidermal pores, or stomata.
Stomatal movement control transpiration
K+ accumulate in the guard
cells during the daylight
The increase of dissolved
substances causes the
movement of water
into the guard cells.
The build-up of water
creates turgor pressure that
causes the guard cells to
bend and the pore to open.
Movement of water through plants
Casparian strip
Pathway along
Endodermal cell
apoplast
Two possibilities for water movements:
Pathway
through
symplast
-pushed up from the roots
-pulled up by the leaves
Pushing Xylem Sap: Root Pressure
•At night, when transpiration is very low, root cells continue
pumping mineral ions into the xylem of the vascular cylinder
Casparian strip
Plasma
membrane
Apoplastic
route
Symplastic
route
Vessels
(xylem)
Root
hair
Epidermis
Root pressure sometimes results in guttation, the
exudation of water droplets on tips of grass blades or the
leaf margins of some small, herbaceous dicots.
Cortex
Endodermis
Vascular cylinder
Pulling Xylem Sap: The Transpiration-Cohesion Tension Mechanism
•Water is pulled upward by negative pressure in the xylem.
•Transpirational pull is facilitated by cohesion and adhesion
Water has a high degree of cohesion due to hydrogen bonding that links
together adjacent water molecules.
Xylem
cells
Adhesion
Cell
wall
Cohesion
the force that allows water
molecules to stick together
Adhesion
the attraction between
different types of molecules
Cohesion and
adhesion in
the xylem
Cohesion,
by
hydrogen
bonding
Xylem
sap
Mesophyll
cells
As water evaporates from the surface of mesophyll cells
in the leaf, the water at the surface is replaced by water
from the interior of the mesophyll.
Stoma
Water
molecule
Transpiration
When water is drawn out, solute concentration increases
and more water is drawn from surrounding cells by
osmosis.
Water potential gradient
Xylem
cells
Cohesion and
adhesion in
the xylem
Atmosphere
Adhesion
Cell
wall
Cohesion,
by
hydrogen
bonding
Water
molecule
Root
hair
The transpirational pull draws water through the xylem, up
the stem all the way from the roots.
Soil
particle
Water
Water uptake
from soil
Senescence and leaf fall are a normal part of plant development
-Occurs in plants as a whole, e.g., annual plants that live only one season.
-Occurs only in parts of plants
-Eliminate leaves before winter
-no photosynthesis
http://theseedsite.co.uk/lifecycle.html
-water loss
-leaves in winter get weighed down by snow
-branches break
-Declining day length is the signal that triggers aging and death
-Chlorophyll is broken
down leaving yellow and
orange accessory pigments
to color the leaves.
Leaf abscission-complex process that results in dropping of leaves
1. Abscission zone is formed at the base of the petiole
2. Thin walled cells form in a separation layer.
3.Cork layer forms inside the separation layer to seal wound when leaf falls.
4. The plant hormone ethylene promotes leaf abscission.
Leaves perform many functions in addition to photosynthesis
Modifications of leaves
tendrils
thread-like structures that help plants
climb over objects and gain access to light
bud scales
waxy modified leaves that prevent
dessication and insulate young
buds in cold weather.
bracts
modified leaves, some of which
are colorful and attract pollinators.
Some leaves are specialized for water or food storage
succulents in arid environments
with modified leaves for water storage
-epiphytes in tropical environments have
modified leaves to store rainwater.
Familiar garden plants have leaves modified to store nutrients
spinach
lettuce
cabbage
edible parts of celery and rhubarb
http://kitchenwaremarketplace.com/blog/the-onion-family/
onions
Leaves are modified for defense in some plants
spines – modified leaf
thorn – modified stem that arises
from the axil of a leaf
Leaves of some plants capture animal prey
-Carnivorous plants which trap live animal prey
prickles - sharp outgrowth from the
epidermis or cortex of the stem.
Humans use leaves in many ways
Botanically- herb- any nonwoody plant
Herbs used in seasoning foods consists of fresh or dried leaves from a variety of woody and nonwoody plants.
Mint family (Lamiaceae)
basil
oregano
rosemary
Carrot family (Apiaceae)
parsley
dill
Different processes are used to extract fragrant oils for perfumes.
Perfume notes derived from leaves include oils of:
-rose
-thyme
-ivy
-cypress
-fig
-tobacco
-tea
cilantro
Waxes
Ex: Copernica cerifera- palm from NE Brazil
Source of carnauba wax which is used
in waxes and shoe polish
Beverages
Natural dyes and fibers can be obtained from the leaves
of number of different plant species.
http://www.bonappetit.com/wp-content
/uploads/2011/08/ice-t-4841.jpg
-leaves of grape (Vitis) (yellow)
-peach Prunus persica (green)
-indigo Indigofera tinctoria (blue)
Henna, an orange dye from the leaves of Lawsonia inermis
Most commercial leaf fibers are obtained from only two
tropical genera:
-Agave –ropes and twines
-Musa textiles – relative of the banana plant
-Manila hemp is derived from the leaves:
http://www.della-giovanna.com/wpcontent/uploads/2013/08/Indian_Wedding_Hena
_Tattoo.jpg
Study outline for Chapter 11-Leaves: Photosynthesis and Transpiration
Define the following terms and label the figures below.
blade
petiole
stipule
axil
node
internode
Distinguish between a simple and a compound leaf.
Distinguish between a pinnately compound leaf and a palmately compound leaf.
Distinguish between the venation of a monocot leaf and a eudicot leaf.
Distinguish between pinnately netted veins and palmately netted veins.
Name the three ways that leaves are arranged along the stem.
Matching
___ palmately compound
___ alternate
___ pinnately compound
___ whorled
___ simple
___ parallel
D.
___ opposite
A.
B.
E.
C.
F.
List the four main types of tissues in leaves and label the image below.
This image shows a mesophytic leaf (Ligustrum; common privet).
What is the function of the epidermis?
What is the function of the mesophyll?
What is the function of xylem?
What is the function of phloem?
G.
Study outline for Chapter 11-Leaves: Photosynthesis and Transpiration
Define xerophyte.
Define mesophyte.
Define hydrophyte.
What is the function of the cuticle?
What is the function of trichomes?
What is the function of the stoma (stomata-pl.)?
Mesophyll tissue is organized into two layers, __________________ and ____________________.
Label the following structures in the eudicot leaf and monocot leaf figures below.
Eudicots
upper epidermis
lower epidermis
bundle sheath
xylem
phloem
palisade layer
eudicot
spongy layer
mesophyll
monocot
What are the differences between the eudicot and monocot leaves?
Label the important structures in a xerophytic leaf, (Nerium leaf; oleander)
cuticle
multiple layer epidermis
palisade parenchyma
spongy parenchyma
trichomes
stomata
vein (with xylem and phloem)
stomatal crypts
Where would you find the stomata in a xerophytic leaf?
What is different about the cuticle and epidermis in the xerophytic leaf?
Label the important structures in a hydrophytic leaf, (Nymphaea leaf; water lily).
cuticle
epidermis
palisade parenchyma
spongy parenchyma
stoma
air space
vein (with xylem and phloem)
Where would you find the stomata in a hydrophytic leaf?
What are the large air spaces for in the hydrophyte?
Monocots
Study outline for Chapter 11-Leaves: Photosynthesis and Transpiration
What are bulliform cells?
How do bulliform cells function?
Define transpiration.
Use the figure below to explain how stomata open and close.
How does water move in the plant from the roots (root pressure)?
Define guttation?
Define adhesion.
Define cohesion.
How does water move in the plant through transpiration pull? Use the picture below to explain.
Xylem
sap
Mesophyll
cells
Stoma
Water potential gradient
Water
molecule
Transpiration Atmosphere
Xylem
cells
Adhesion Cell
wall
Cohesion,
Cohesion and by
adhesion in hydrogen
the xylem
bonding
Water uptake
from soil
Water
molecule
Root
hair
Soil
particle
Water
What types of plants senesce?
What parts of the plant senesce?
Why does the plant eliminate leaves in winter?
Explain how the leaf abscission-complex process results in plants dropping their leaves.
Study outline for Chapter 11-Leaves: Photosynthesis and Transpiration
Define the following terms and label the images below.
tendril
bud scale
bract
spine
thorn
prickle
What is an example of a carnivorous plant?
Why are carnivorous plants found in low nitrogen soil?
Define herb.
Give examples of herbs from the Lamiaceae (mint family).
Give examples of herbs from the Apiaceae (carrot family).
Define note. Give examples of perfume derived from the oil of leaves.
Give examples of plant sources for natural dyes.
Give examples of plant sources for waxes.
Give examples of plant sources for beverages.
Give examples of plant sources for plant fibers.