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.

In monocots, such as lilies and grasses, the leaf expands out in a sheath.

Some leaves lack petioles and are termed sessile.

Leaf blade variation

-compound

-simple

There are 2 types of compound leaves:

Leaves also possess a wide variety of patterns

of veins which contain xylem and phloem

Pinnately netted veins Palmately netted veins

Leaves can be arranged along a stem in a number

of different ways

smooth toothed deeply lobed

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

Monocots Eudicots

Parallel Netted

Elm Norway maple

alternate opposite whorled

Leaves are complex structures composed of 4 main types of tissues:

The structure of the leaf is dependent on the plant’s environment

Epidermis

Mesophytes Hydrophytes Xerophytes

-epidermis -tough outer cell layer of the leaf that protects

inner tissues and provides structural support

-mesophyll -main photosynthetic tissue of the leaf

-xylem

-conducting tissues which form the vascular bundles

-phloem or veins of the leaf

Epidermal cells secrete a waxy layer (cuticle) which help retard water loss

hydrophytes plants growing in wet environments

xerophytes plants with leaves adapted to dry environments

mesophytes plants that require moderately moist environments

Epidermis

Trichomes serve a variety of functions:

Mesophyte Hydrophyte

The upper epidermis of grass leaves has another specialized type of cell- bulliform cell.

Epidermal cells may be specialized to form hairs called trichomes.

Epidermal tissue typically contains many thousands of

minute pores called stomata (sing. stoma).

Each stoma consists of a pore surrounded by two guard cells.

Xerophytes

When the stomata open, water vapor and oxygen move out of the leaf

and carbon dioxide moves into the interior of the leaf.

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.

Xylem and phloem are the conducting tissues of leaf veins

Mesophyll tissue is organized in 2 layers:

The intracellular spaces facilitates gas exchange and is connected to the

external atmosphere by stomata

Mesophyll is located between the upper and lower epidermis

Mesophyll cells are:

Eudicots Monocots

Xylem conducts water and dissolved minerals to 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.

-Distinct palisade

and spongy layers

in eudicot

-Mesophyll is not

differentiated into

distinct palisade

and spongy parenchyma

in monocots

-Bundle sheath cells

are also very conspicuous

in monocots

Phloem conducts dissolved sugars from the leaf tissues.

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

Movement of water through plants

Two possibilities for water movements:

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 Endodermal cell Pathway along

apoplast

Pathway through symplast

Casparian strip

Plasma membrane

Apoplastic route

Symplastic route

Root hair

Vessels (xylem)

Cortex Endodermis Epidermis Vascular cylinder

The build-up of water

creates turgor pressure that

causes the guard cells to

bend and the pore to open.

The increase of dissolved

substances causes the

movement of water

into the guard cells.

K+ accumulate in the guard

cells during the daylight

-pushed up from the roots

-pulled up by the leaves

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.

Pulling Xylem Sap: The Transpiration-Cohesion Tension Mechanism

•Water is pulled upward by negative pressure in the xylem.

Cohesion

Adhesion

•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 sap

Mesophyll cells

Stoma

Water molecule

Atmosphere Transpiration

Xylem cells

Adhesion Cell wall

Cohesion, by hydrogen bonding

Cohesion and adhesion in the xylem

Water molecule

Wa

ter

po

ten

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l g

rad

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Root hair

Soil particle

Water

Water uptake from soil

Xylem cells

Adhesion Cell wall

Cohesion, by hydrogen bonding

Cohesion and adhesion in the xylem

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.

When water is drawn out, solute concentration increases

and more water is drawn from surrounding cells by

osmosis.

The transpirational pull draws water through the xylem, up

the stem all the way from the roots.

the force that allows water

molecules to stick together

the attraction between

different types of molecules

Leaf abscission-complex process that results in dropping of leaves

Leaves perform many functions in addition to photosynthesis

Modifications of leaves

tendrils bud scales

bracts

-Occurs in plants as a whole, e.g., annual plants that live only one season.

-Eliminate leaves before winter

-Declining day length is the signal that triggers aging and death

-Occurs only in parts of plants

1. Abscission zone is formed at the base of the petiole

3.Cork layer forms inside the separation layer to seal wound when leaf falls.

4.

-no photosynthesis

-water loss

-leaves in winter get weighed down by snow

-branches break

-Chlorophyll is broken

down leaving yellow and

orange accessory pigments

to color the leaves.

http://theseedsite.co.uk/lifecycle.html

2. Thin walled cells form in a separation layer.

The plant hormone ethylene promotes leaf abscission.

Senescence and leaf fall are a normal part of plant development

thread-like structures that help plants

climb over objects and gain access to light

waxy modified leaves that prevent

dessication and insulate young

buds in cold weather.

modified leaves, some of which

are colorful and attract pollinators.

Some leaves are specialized for water or food storage

cabbage

lettuce

edible parts of celery and rhubarb onions

Leaves are modified for defense in some plants

Leaves of some plants capture animal prey

-Carnivorous plants which trap live animal prey

Familiar garden plants have leaves modified to store nutrients

succulents in arid environments

with modified leaves for water storage

-epiphytes in tropical environments have

modified leaves to store rainwater.

spinach

http://kitchenwaremarketplace.com/blog/the-onion-family/

spines – modified leaf thorn – modified stem that arises

from the axil of a leaf

prickles - sharp outgrowth from the

epidermis or cortex of the stem.

Humans use leaves in many ways

Botanically- herb- any nonwoody plant

Mint family (Lamiaceae)

Carrot family (Apiaceae)

Different processes are used to extract fragrant oils for perfumes.

Perfume notes derived from leaves include oils of:

Herbs used in seasoning foods consists of fresh or dried leaves from a variety of woody and nonwoody plants.

basil oregano rosemary

parsley dill cilantro

-rose

-thyme

-ivy

-cypress

-fig

-tobacco

-tea

Waxes

Beverages

Natural dyes and fibers can be obtained from the leaves

of number of different plant species.

Most commercial leaf fibers are obtained from only two

tropical genera:

Ex: Copernica cerifera- palm from NE Brazil

Source of carnauba wax which is used

in waxes and shoe polish

-Musa textiles – relative of the banana plant

-Agave –ropes and twines

http://www.bonappetit.com/wp-content

/uploads/2011/08/ice-t-4841.jpg

Henna, an orange dye from the leaves of Lawsonia inermis

http://www.della-giovanna.com/wp-

content/uploads/2013/08/Indian_Wedding_Hena

_Tattoo.jpg

-Manila hemp is derived from the leaves:

-leaves of grape (Vitis) (yellow)

-peach Prunus persica (green)

-indigo Indigofera tinctoria (blue)

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

___ opposite

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.

A. B. C.

D. E. F.

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.

upper epidermis

lower epidermis

bundle sheath

xylem

phloem

palisade layer

spongy layer

mesophyll

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?

eudicot

monocot

Eudicots Monocots

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?

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.

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.

Xylem sap

Mesophyll cells Stoma

Water molecule

Atmosphere Transpiration

Xylem cells

Adhesion Cell wall

Cohesion, by hydrogen bonding

Cohesion and adhesion in the xylem

Water molecule

Wa

ter

po

ten

tia

l g

rad

ien

t

Root hair Soil particle

Water Water uptake from soil

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.