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Plant Anatomy and Nutrient Transport Chapter 43

Plant Anatomy and Nutrient Transport Chapter 43. In order to survive, plants have to… The best ways to appreciate plants is to consider how they overcome

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Page 1: Plant Anatomy and Nutrient Transport Chapter 43. In order to survive, plants have to… The best ways to appreciate plants is to consider how they overcome

Plant Anatomy and Nutrient Transport

Chapter 43

Page 2: Plant Anatomy and Nutrient Transport Chapter 43. In order to survive, plants have to… The best ways to appreciate plants is to consider how they overcome

In order to survive, plants have to…The best ways to appreciate plants is to consider how they

overcome the challenges encountered by life on Earth

Obtain energy Obtain water and other nutrients Distribute water and nutrients through the body Exchange gases Support the body Grow and develop Reproduce

Evolution has produced a variety of different types of plants

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Plant body Organization

• Two major parts – The root system of a plant – The shoot system

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Root Systems

• Branched portions of the plant body • Embedded in the soil• Six functions -

– Anchor the plant – Absorb water and minerals from soil – Store surplus food, carbohydrates manufactured in the shoot– Transport water, minerals, sugars, hormones to and from shoot – Produce hormones – Interact with soil fungi and bacteria that help provide nutrients to

the plant

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The Shoot

The shoot system is buds, leaves, flowers, fruits - all on parts of stems • Buds give rise to leaves or flowers • Leaves - sites of photosynthesis • Flowers - reproductive organs, producing male and female gametes,

then help them to reach one another • Flowers produce seeds enclosed within fruits (protect and aid in

dispersal)

Stems - branched, elevate the leaves, flowers, fruit• Elevating the fruit helps disperse the seeds • Some parts are specialized to transport water, minerals,

food molecules, others produce hormones

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Two groups of flowering plants

Monocots - lilies, daffodils, tulips, palm trees, grasses— lawn grasses, and wheat, rice, corn, oats, bamboo

Dicots - “broad-leafed” plants, including deciduous trees, bushes, vegetables, and flowers in fields and gardens

There are differences between monocots and dicots, but the characteristic that gives these groups their name is the number of cotyledons

The part of a plant embryo that absorbs and stores food reserves in the seed, then transfers the food to the rest to the embryo when the seed sprouts

Monocots have a single cotyledon Dicots have two cotyledons

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structures

leaf primordiaapical meristem

leaf

terminal bud

branch roots

lateral bud

flower

stem

branch

fruit

blade

petiole

node

root hairsroot cap

energy acquisitionby photosynthesis;gas exchange

reproduction

body support;transport of waterand nutrients

Acquisitionof water andminerals

reproduction

growth anddevelopment ofplant structures

functions

root

shoo

t sys

tem

root

sys

tem

The Structures and Functions of a Flowering Plant

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Characteristics of Monocots and Dicots Flowers Leaves Roots SeedsStems

cotyledon

embryo

cotyledons

embryo

Flower parts are inthrees or multiplesof three

Flower parts are infours or fives or multiplesof four or five

Leaves have smooth edges,often narrow, with parallel veins

Leaves are palmate (handlike)or oval with netlike veins

Vascular bundlesare scatteredthroughout the stem

Monocots have afibrous root system

The seed has onecotyledon (seed leaf)

The seed hastwo cotyledons(seed leaves)

Dicots have ataproot system

Vascular bundlesare arranged in aring around the stem

Dic

ots

Mon

oco

ts

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Plant Development

Dramatically different from animalsOne difference - timing and distribution of growth

In animals, the proportions of a newborn differs from an adult, parts of a newborn’s body grow until they reach adult size and structure, then growth stops

Flowering plants grow throughout their lives, never reaching a stable adult body form

Most plants grow longer or taller only at the tips of their branches and roots

A swing tied to a tree branch or initials carved in tree bark do not move farther up from the ground as the tree grows

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Plants are composed of two types of cells

• During plant growth, meristem cells give rise to differentiated cells

– Meristem cells, like animal stem cells, are unspecialized and capable of mitotic cell division

– Some daughter cells lose the ability to divide and become differentiated cells, with specialized structures and functions

• Continued division of meristem cells keep the plant growing throughout its life• Differentiated daughter cells form the non-growing parts of the plant, as leaves

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Where Growth Occurs• Plants grow as a result of cell division and differentiation of

meristem cells found in two general locations –

– Apical meristems - located at the tips of roots and shoots • Growth produced by apical meristem cells is primary

growth• Increase in the height or length of a shoot or root,

development of specialized parts of the plant - leaves and buds

– Lateral meristems (side meristems, cambium) - concentric cylinders of meristem cells

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Animation: Primary Growth

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Secondary Growth Division of lateral meristem cells and differentiation of their daughter cells

produce further concentric cylinders of secondary growth, an increase in the diameter and strength of roots and shoots – Occurs in woody plants - deciduous trees, shrubs, conifers – Some woody plants become very tall and thick and may live hundreds to thousands of

years

Many plants do not undergo secondary growth

– Plants that lack secondary growth are soft bodied, with flexible, fairly short stems

– These herbaceous, typically short-lived plants include lettuce, beans, lilies, and grasses

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Tissues and Cell Types? As meristem cells differentiate, they produce a variety of

cell types – One or more specialized types of cells work

together to perform a specific function, as conducting water and minerals = tissue

– Functional groups of more than one tissue = tissue systems • Dermal tissue system covers the outer surface of the

plant • Ground tissue system makes up the body of young

plants; its functions include photosynthesis, storage, and support • Vascular tissue system transports fluids throughout the

plant body

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Tissues and Cell Types

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Dermal Tissues• Dermal tissue system covers the plant body – Two types of dermal tissues: • epidermal tissue • periderm

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Epidermal Tissues Epidermal tissue forms the epidermis - outermost cell layer covering the

leaves, stems, and roots of all young plants, also covers flowers, seeds, and fruit – In herbaceous plants, it forms the outer covering of the entire

plant body throughout its life – Above ground - generally composed of tightly packed, thin-

walled cells, covered with waterproof, waxy cuticle secreted by the epidermal cells • The cuticle reduces the evaporation of water from the plant and helps protect

it from the invasion of disease microorganisms

– Adjustable pores regulate the movement of water vapor, O2, and CO2 across the epidermis of leaves and young stems

– In contrast, the epidermal cells of roots are not covered with cuticle that would prevent them from absorbing water and minerals

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PeridermReplaces epidermal tissue on the roots and stems of

woody plants as they age

Composed of multiple layers of cork cells on the outside of the root or stem and a layer of lateral meristem tissue - cork cambium - that generates the cells • Cork cells produce thick, waterproof cell walls as they grow,

then die as they reach maturity • Because of multiple layers of waterproof cork cells on their

surface, root segments that are covered with periderm help anchor the plant in the soil, but can not absorb water and minerals

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Ground Tissue

Compromises most of the young plant body

– All of the tissue of the plant body except dermal and vascular tissues

– Three types of ground tissues are parenchyma, collenchyma, and sclerenchyma

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Parenchyma Parenchyma - most abundant - makes up most of young plant body – The cells - called parenchyma cells - have thin cell walls

and are alive at maturity – They carry out the plant’s metabolic activities,

photosynthesis , secretion of hormones, food storage • Potatoes, seeds, fruits, storage roots are packed with

parenchyma cells that store sugars and starches

– Help to support the bodies of many plants, especially herbaceous plants

– Some cells can divide – In addition to making up much of the ground tissue

system, parenchyma cells are found in periderm and vascular tissues

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Parenchyma

(a) Parenchyma cells in a white potato

thin cell wall

stored starch

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Collenchyma Cells that are elongated, with thickened but flexible cell walls

– Alive at maturity, generally cannot divide – Collenchyma tissue provides support for entire

body of young and non-woody plants, the leaf stalks, or petioles, of all plants • Celery stalks are thick petioles, are supported by “strings”

composed of collenchyma cells

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(b) Collenchyma cells in a celery stalk

thick cell wall

Collenenchyma

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Sclerenchyma Composed of cells with thick, hardened cell walls

– Sclerenchyma cells support and strengthen the plant body; they die after they differentiate

– Their thick cell walls then remain as a source of support • Sclerenchyma cells form nut shells and the outer

covering of peach pits • Scattered throughout the parenchyma cells in a pear,

sclerenchyma cells give pears their gritty texture • Sclerenchyma cells support vascular tissues and form an

important component of wood

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(c) Sclerenchyma cells in a pear

thick cell wall

Sclerenenchyma

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• Transports water and nutrients – Conducts water and dissolved substances throughout the body – Consists of two conducting tissues: xylem and phloem

The Vascular Tissue System

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Xylem Transports water and dissolved minerals from the roots to the rest of the

plant, only in one direction.

– In angiosperms, xylem contains supporting sclerenchyma fibers and two specialized conducting cell types: tracheids and vessel elements

– Both tracheids and vessel elements develop thick cell walls, then die as their final step of differentiation, leaving hollow tubes of nonliving cells wall

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Xylem Tissues

• Tracheids - thin, elongated cells stacked atop one another – Tapered, overlapping cells resemble the tips of hypodermic needles – The ends and sides of tracheids contain pits - porous dimples in the

walls that separate adjacent cells – Because the cell wall in a pit is both thin and porous, water and

minerals pass freely from one tracheid to another an adjacent vessel element

• Vessel elements - larger in diameter than tracheids, form pipelines called vessels – Vessel elements are stacked end to end – Their adjoining end walls may be connected by fairly large holes or

the walls may disintegrate, leaving an open tube

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Animation: Xylem Adaptations

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tracheids

pits

end wall

vesselelement

Xylem

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Phloem Transports sugars and other organic molecules throughout the

plant body – Transports sugars, amino acids, and hormones—from structures that

synthesize them to structures that need them – Transports fluids up or down the plant, depending on the metabolic

state of the parts of the plant at any given time

• Two cell types: sieve-tube elements and companion cells – Sieve-tube elements - joined end to end to form pipes

• As sieve-tube elements mature, they lose their nuclei and other organelles, only a thin layer of cytoplasm lining the plasma membrane

– The junction between two sieve-tube elements is a sieve plate • Membrane-lined pores connect the insides of two sieve-tube

elements, allowing fluid to move from one cell to the next

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Sieve-tube Cells• Sieve-tube function requires an intact plasma membrane – How, then, can sieve-tube elements maintain and

repair their plasma membranes when they lack nuclei and most other organelles? • Life support of sieve-tube elements is provided by smaller,

adjacent companion cells, which are connected to sieve-tube elements by pores called plasmodesmata

• Companion cells help maintain the integrity of the sieve-tube elements by providing them with proteins and high-energy compounds such as ATP

– Like xylem, phloem also contains supporting sclerenchyma fibers

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sieve plate

companioncell

companion cell

sieve-tubeelement

Phloem

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Leaves Major photosynthetic structures of most plants

– Their green color arises from chlorophyll molecules – Shape and structure of leaves has evolved in response to

environmental challenges that plants face in obtaining the essentials for photosynthesis: sunlight, carbon dioxide (CO2), and water

Water is absorbed from the soil by the roots and transported to leaves by the xylem – Assuming adequate water supply, maximum photosynthesis

would occur in a porous leaf (allows CO2 to diffuse easily from air to the leaf) with a large surface area

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Land plants cannot always get enough water from soil – On a hot, sunny day - large, porous leaf loses more

water through evaporation than the plant could replace

– The leaves of flowering plants are an compromise between conflicting demands • They have a large, waterproof surfaces with adjustable

pores that can open and close to admit CO2 or restrict water evaporation

Leaves are a compromise…

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Angiosperm Leaves A broad, flat portion - the blade is connected to the

stem by a stalk, or petiole – The petiole positions the blade – Inside, vascular tissues provide a conducting system

between the leaf and the rest of the plant

The epidermis regulates movement of gases in and out – Leaf epidermis is a layer of nonphotosynthetic, transparent

cells that secrete a waxy cuticle on the outer surfaces – The cuticle is waterproof and reduces evaporation

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Stomata (stoma) Adjustable pores in the cuticle and epidermis,

they regulate the diffusion of CO2, O2, water vapor in and out – Two sausage-shaped guard cells that enclose and

adjust the size of the opening – Unlike the other epidermal cells, guard cells contain

chloroplasts and carry out photosynthesis

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Functions of Leaves• Photosynthesis occurs in mesophyll cells – The transparent epidermal cells allow sunlight to reach

the mesophyll (“middle of the leaf”), which consists of loosely packed cells containing chloroplasts • Mesophyll cells carry out most of the photosynthesis of a

leaf • Air spaces between mesophyll cells allow CO2 from the

atmosphere to diffuse to each cell and O2 produced during photosynthesis to diffuse away

– Many leaves possess two types of mesophyll cells—an upper layer of columnar palisade cells and a lower layer of irregularly shaped spongy cells

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Vascular Bundles• Veins transport water and nutrients throughout the

leaf – Vascular bundles (veins) contain xylem and phloem – Conduct materials between leaf and the rest of the plant

• Veins send thin branches to each photosynthetic cell • Xylem delivers water and minerals to the mesophyll cells of the

leaf, and phloem carries away the sugar they produce during photosynthesis

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upper epidermis

petioleblade

mesophyll

palisadelayer

spongylayer

lowerepidermis stoma guard cell chloroplasts

xylem phloem

vascular bundle

cuticle

cuticle bundle-sheathcell

A Typical Dicot Leaf

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Structures and Functions of Leaves Temperature, availability of water and light have exerted

selection pressure on leaves – Dim light - the floor of a tropical rain forest - very large leaves,

low light level and abundant water – Desert-dwelling cacti have spines , no surface area for

evaporation– Plump leaves of succulents store water in the central vacuoles of

their cells and are covered with a thick cuticle to reduces water evaporation

– Some plants have surprising structures and functions, including storing nutrients, capturing prey, or climbing

– Onions, Venus Flytraps, Pea plant tendrils

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Specialized Leaves

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Stems Support and separate the leaves, lifting them to the sunlight

and air – Stems transport water and dissolved minerals from the roots up

to the leaves – They also transport sugars produced in the photosynthetic parts

of the shoot to the roots and other parts of the shoot, such as buds, flowers, and fruits

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Adaptations of stems

• Potato eyes• Strawberry runners• Grapes and ivies with grasping tendrils• thorns

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Cork

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Functions of Roots

• Anchor plant• Absorb water and mineral• Store water and food

• Dicots generally have taproots• Monocots have fibrous root systems

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Taproots and Fibrous Roots

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Structures of Roots?

• 4 distinct regions– Root cap– Epidermis– Cortex– Vascular cylinder

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root hairepidermis

cortex

endodermisof cortex

pericycle

xylem

phloem

apicalmeristem

vascularcylinder

rootcap

Primary Growth in Roots

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Root Cap

• Primary growth in a root• Protects apical meristem• Thick cell walls, lubricant• Continuously replaced

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Epidermis

• Permeable to water and minerals

• No cuticle• Epidermal cells grow root

hairs to increase surface area

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Root Hairs

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Cortex

• Located between the epidermis and vascular cylinder

• Large, loose packed parenchyma with porous cell walls

• Sugar is transported to these cells and stored as starch

• Innermost layer, endodermis circles vascular cylinder– Caspian Strip (more later) – waxy

on top bottom, sides but not inner/outer faces

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Vascular Bundle - Pericycle

• Pericycle – outermost layer– Regulate movement of

minerals and water into xylem– Source of branching in roots– Hormone release causes

formation of branch root– Punches out through

epidermis, cortex by crushing and releasing enzymes

• Xylem and Phloem

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Branch Roots

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Specialized Roots

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Secondary Growth

• Similar but not identical to secondary growth in stems– Vascular cambium produces secondary xylem and

phloem in the root interior– Cork cambium produces cork cells on the outside

of the root

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Essential Nutrients

• Plants only need inorganic nutrients because they can make their own organic molecules

• Macronutrients – needed in large quantity• Micronutrients - <1% total nutrients needed

CO2 - O2 - H

Minerals (K, Ca)Ionic compounds – nitrate, phosphateWater

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Water is crucial

• Transport minerals, sugars, hormones and other organic molecules

• Plants require a large amount of water• Source is soil

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Roots Transport Minerals

• Absorb mineral from soil and transport to xylem

• Minerals must be dissolved in soil water• Transported from root to shoot in tracheids

and vessel elements of xylem

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Young Root Structure

• Living cells• Extracellular space• Tracheids and vessel elements (dead)

• Cell walls are all very porous• Caspian strip divides extracellular space into

two compartments – inside (vascular bundle) and outside

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vascular cylinder

xylem

pericycle endodermis

endodermalcells

Casparian strip

cell walls

soil particles

water

roothair

air

plasmodesmata

cortex epidermis

12

3

45

(a) Pathways of mineral and water uptake

(b) Endodermal cells, showing the Casparian strip

Mineral and Water Uptake by Roots

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Mineral and water uptake

1. Minerals dissolved in water fill space between cells (blue)2. Minerals are actively transported across plasma

membrane of root hairs, epidermal, cortex, and outside face of endodermal cells; water follows by osmosis (black)

3. Minerals diffuse from cell to cell through plasmodesmata (red)

4. Minerals diffuse or are actively transported across plasma membanes of pericycle cells; water follows by osmosis

5. Minerals and water enter tracheids and vessel elements of xylem (blue)

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Importance of the caspian strip

• Soil water in the outer root compartment has low concentration of mineral

• Inner compartment has higher concentration• = diffusion gradient• The caspian strip prevents movement of

minerals from inner outer compartments

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Author Animation: Xylem Transport

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Root Pressure

• Water moves by osmosis from the soil, across plasma membranes and into the tracheids and vessel elements of the roots

• Sometimes this pressure is so strong it causes root pressure – water entering pushes minerals up the root into the shoot and the water droplets can be visible on the leaves

• This is influenced by transpiration –evaporation of water from the leaves

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Root Pressure

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Symbiotic Relationships

• Mutually beneficial relationships• Fungal mycorrhizae – fungi in a symbiotic relationship

with plant roots.• Fungal strands twine between roots, increasing area of

root in contact with soil• Some fungi can extract elements that plants cannot, ie.

Phosphates• Fungus receives sugars, amino acids, vitamins from

plant– Desert and high altitude locations– In some forested areas the mycorrhizae interlink trees of

different species, allowing nutrient exchange between them

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Mycorrhizae: A Root–Fungus Symbiosis

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Nitrogen-fixing bacteria

• Plants can only use N in form of ammonia or nitrate

• Legumes – peas, alfalfa, soy beans• Symbiotic relationship with bacteria that are

able to fix nitrogen (N2 NH3)• Bacteria enter cell and move to cortex where

they form a nodule• Use plant nutrients

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Nodules House Nitrogen-Fixing Bacteria

nitrogen-fixing bacteria withincortex cells of nodules

epidermis

nodule

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Transpiration

• 90% of water absorbed is lost through the stomata of the leaves, minerals are carried along with the water

• Cohesion – tension theory = water is pulled up the tree by transpiration– Cohesion – attraction between water molecules, forms a

chain-like column within the xylem– Tension – chain of water is pulled up xylem by tension

produced by evaporation from leaves

– Redwood trees that are 350 ft. tall

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2

1

3

water molecules

Waterevaporatesthrough thestomata of leaves

Water entersthe vascularcylinder of theroot

Cohesion ofwater moleculesto one another byhydrogen bondscreates a “waterchain”

flow

of w

ater

The Cohesion–Tension Theory

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Author Animation: Cohesion and Adhesion

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Amazon Rain Forest

• Warm weather and abundant rainfall

• Supports hundreds of trees per acre

• Humidity partially due to transpiration

• When clearcut, local climate is much drier and hotter

• Read page 858

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Stomata Regulation

• Mechanically – how is the size changed?• Physiologically – how do they respond to stimuli?

• Two guard cells, slightly curved. • Cellulose fibers encircle the cells

• K+ enters cells in response to light and CO2 conc., water follows by osmosis

• Cellulose belts prevent cells from getting fatter so they get longer, curve outward – open central pore

• Closes when it loses water

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Stomata

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How Guard Cells Open a Stoma K+ entersthe guard cells(red arrows)

1

Water followsby osmosis(blue arrows)

2

The guardcells lengthenand bendoutward

3

The poreopens4

cellulose“belts”

K+ ions

pore

guardcells

(a) Closed stoma (b) Opening a stoma

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How is sugar transported?

• Synthesized in leaves, carried by phloem• Botanists use aphids to learn how phloem

works

• Chemical analysis of phloem fluid = 12-20% sugar, +amino acids, protein and hormones

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Aphids Feed on the Sugary Fluid in Phloem Sieve Tubes

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Pressure-flow theory

• Differences in water pressure drive flow of fluid through sieve tubes

• Pressure differences are created by the production and use of sugars– Sugar source – synthesizes more than uses– Sugar sink – uses more than it synthesizes– May be source or sink depending on season• Roots, sink – summer (conv. sugar to starch)• Roots, source – following spring (conv. starch to sugar)

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How it works

1. Sugar produce in source cell, transported to phloem

2. Water from xylem follows sugar into phloem, increasing pressure

3. Water pressure drives fluid to regions of lower pressure

4. Cells of sugar sink transport sugar out of phloem, water follows by osmosis = lower pressure

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The Pressure-Flow Theory of Sugar Transport in Phloem

xylem vessel phloem sieve tube

sugarsink

sugar source

sugar sourcecell

sugar sinkcell

sunlight

1

2

3

4

Fig. 43-25

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Author Animation: Phloem Transport

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Why do leaves turn color in the fall?

• Fall - temperatures cool, days are long and sun is bright

• Photosynthetic pathways are less efficient, leaf cannot use all light available

• Excess light harms chloroplasts• Red pigmented leaves – anthocyanin – are better

protected against intense light• Why protect? Complex molecules in the leaves are

broken down and stored in cells in the root and stem. Photosynthesis must continue to provide energy for this process