Chapter24.25

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Biology

Sylvia S. Mader Michael Windelspecht

Chapter 24 And 25

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24.1 Organs of Flowering Plants

• Flowering plants, or angiosperms, are extremely diverse but share many common structural features.

• Most flowering plants possess a root system and a shoot system

 Theroot systemsimply consists of the roots,

 Theshoot systemconsists of the stem and leaves.

• A typical plant features three vegetative organs

 roots, stems, and leaves

 Vegetative organs are concerned with growth and nutrition.

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3 stem

internode leaf

petiole blade

axillary bud terminal bud

node

vascular tissues

root hairs

primary root branch root shoot system

root system node vein

Organs of Flowering Plants

• Roots

 Generally, the root system is at least equivalent in size and extent to the shoot system

• Anchors plant in soil

• Absorbs water and minerals from the soil • Produces hormones

 Root hairs:

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Organs of Flowering Plants

• Stems



Shoot system of a plant is composed of the

stem

, branches, and leaves

• Stem is the main axis of a plant that elongates and produces leaves

– Nodesoccur where leaves are attached to the stem

– Internodeis region between nodes

– Axillary buds can produce new branches of the stem (or flowers)

• Stem also has vascular tissue that transports water and minerals

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Organs of Flowering Plants

• Leaves



major part of the plant that carries on

photosynthesis

• Foliage leaves are usually broad and thin

– Blade- Wide portion of foliage leaf

– Petiole- Stalk attaching blade to stem

– Leaf Axil - Upper acute angle between petiole and stem where the axillary bud is found

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Eudicots

7

blade

petiole

c. Leaves, pumpkin seedling b. Shoot system, bean seedling

a. Root system, dandelion

lateral root roots

stem

stems

Organs of Flowering Plants

• Monocots

(Single cotyledon)



Cotyledons act as transfer tissue

• Nutrients are derived from the endosperm



Root vascular tissue occurs in ring



Parallel leaf venation



Flower parts arranged in multiples of three

• Eudicots

(Two cotyledons)



Cotyledons supply nutrients to seedlings



Root phloem located between xylem arms



Netted leaf venation



Flower parts arranged in multiples of four or

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Flowering Plants are Either

Monocots or Eudicots

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Stem Leaf

Seed Root Flower

M

o

n

o

c

o

ts

E

udi

c

ot

s

One cotyledon in seed

Root xylem and phloem in a ring

Leaf veins form a parallel pattern

Flower parts in threes and multiples of three

Root phloem between arms of xylem

Leaf veins form a net pattern

Flower parts in fours or fives and their multiples

Two cotyledons in seed

Vascular bundles in a distinct ring Vascular bundles scattered in stem

24.2 Tissues of Flowering

Plants

• Meristematic tissue enables flowering

plants to grow throughout their lifetime

• Apical meristems

at the tips of stems and

roots increase the length of these tissues

• Apical meristem produces three types of

meristem

, which produce three

specialized tissues



Epidermal tissue



Ground tissue

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11

Tissues of Flowering Plants

• Epidermal Tissue

 Forms the outer protective covering of a plant

 Epidermiscontains closely packed epidermal cells

• Epidermal cells exposed to air are covered with waxy cuticle

• Root epidermal cells have root hairs

• Epidermal cells of stems, leaves, and reproductive organs have trichomes

• Lower leaf surface contains stomata

 In older woody plants, the epidermis of the stem is replaced by periderm

• Major component is cork

• New cork is made by cork cambium

Modifications of Epidermal Tissue

corn seedling

root hairs

enlongating root tip a. Root hairs

guard cell chloroplasts

b. Stoma of leaf

Stoma nucleus

lenticel

periderm cork cork cambium

c. Cork of older stem

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Tissues of Flowering Plants

• Ground tissue forms bulk of a flowering plant

 Parenchyma cells:

• Least specialized and are found in all organs of plant • Can divide and give rise to more specialized cells

 Collenchymacells:

• Have thicker primary walls

• Form bundles underneath epidermis

• Provide flexible support for immature regions of the plant

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Tissues of Flowering Plants



Ground tissue (continued)

• Sclerenchyma

cells:

– Have thick secondary walls impregnated with

lignin

– Most are nonliving

– Primary function is to support mature regions of the plant

– Two types of sclerenchyma cells »Fibers

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Ground Tissue Cells

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a. Parenchyma cells b. Collenchyma cells c. Sclerenchyma cells

(All): © Biophoto Associates/Photo Researchers, Inc.

50 mm 50 mm 50 mm

Tissues of Flowering Plants

• Vascular Tissue



Xylem

transports water and minerals from the

roots to the leaves

• Tracheids

– Long, with tapered ends

– Water moves across pits in end walls and side walls

– Vascular rays between rows of tracheids conduct water across the width of the plant

• Vessel Elements

– Larger, with perforated plates in their end walls – Form a continuous vessel for water and mineral

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Xylem Structure

17

a. Xylem micrograph (left) and drawing (to side)

pits vessel

element

tracheids

tracheid

pitted walls

xylem parenchyma

cell

perforation plate

c. Tracheids vessel

element

a: © J. Robert Waaland/Biological Photo Service 50 mm

b. T wo types of vessels

Tissues of Flowering Plants

• Vascular Tissue



Phloem

transports sucrose and other organic

compounds from the leaves to the roots

• Sieve-tube members function as conducting cells

– Contain cytoplasm, but lack nuclei – Sieve plate – cluster of pores in wall

• Each sieve-tube member has a companion cell – Plasmodesmata connect the two

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Phloem Structure

19

a: © George W ilder/Visuals Unlimited

b. Sieve-tube member and companion cells nucleus sieve plate

sieve plate sieve-tube member

companion cell

a. Phloem micrograph (left) and drawing (to side) phloem parenchyma

cells sieve-tube

member

companion cell

20 mm

25.2 Water and Mineral Uptake

• Water and minerals enter the roots of flowering

plants through the same pathways

 Between porous cell walls, then forced into endodermal cells by the Casparian strip

 Through root hairs, through cells across the cortex and endodermis via cytoplasmic strands within

plasmodesmata

• Water enters root cells when their osmotic

pressure is lower than that of the soil

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Water and Mineral Uptake

21

50 µm

Water and Mineral Uptake

endodermis

pericycle

phloem

xylem

cortex

50 µm

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23

endodermis

pericycle

phloem xylem cortex

50 µm

Water and Mineral Uptake

endodermis

pericycle

phloem xylem cortex

50 µm

vascular cylinder

pericycle

endodermis and Casparian strip

cortex

pathway A of water and

minerals epidermis

pathway B of water and

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Water and Mineral Uptake

25

endodermis

pericycle

phloem

xylem cortex

50 µm

pericycle

cortex

root hair

minerals

a. b.

Water and Mineral Uptake

endodermis

pericycle

phloem

xylem

cortex

50 µm

cortex

root hair

minerals

a. b.

H+

pericycle

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27 + endodermis pericycle phloem xylem cortex 50 µm vascular cylinder cortex pathway A of water and

root hair

minerals

a. b.

ADP P

ATP _H+

pericycle

Water and Mineral Uptake

1 endodermis pericycle phloem xylem cortex 50 µm vascular cylinder cortex pathway A of water and

root hair

minerals

a. b.

Water Outside Endodermal Cell ATP

An ATP-driven pump transports H+ _{out of cell.}

H+

H+ H+

+ ADP P pericycle endodermis and Casparian strip

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Water and Mineral Uptake

29 2 1 endodermis pericycle phloem xylem cortex 50 µm vascular cylinder cortex pathway A of water and

root hair

minerals

a. b.

H+

H+ H+

The electro chemical gradient causes K+

to enter by way of a channel protein. + ADP P pericycle endodermis and Casparian strip

An ATP-driven pump transports H+ _{out of cell.}

Water and Mineral Uptake

2 1 endodermis pericycle phloem xylem cortex 50 µm vascular cylinder cortex pathway A of water and

root hair

minerals

a. b.

H+

H+ H+

K+

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Negatively charged ions (I-_{) are transported}

along with H+_{into cell.}

2 3 1 endodermis pericycle phloem xylem cortex 50 µm vascular cylinder cortex pathway A of water and

root hair

minerals

a. b.

to enter by way of a channel protein.

H+

H+ H+

H+ I

-K+ K+ K+ K+ + ADP P pericycle endodermis and Casparian strip © CABISCO/Phototake An ATP-driven pump transports H+ _{out of cell.}

Water and Mineral Uptake

Negatively charged ions (I-) are transported along with H+into cell.

H+ I -2 3 1 endodermis pericycle phloem xylem cortex 50 µm vascular cylinder cortex pathway A of water and

root hair

minerals

a. b.

Water Outside Endodermal Cell ATP Endodermal Cell H+ H+ H+ H+

H+ H+

H+ I -I -I -K+ K+ K+ K+

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Water and Mineral Uptake

• Adaptations of roots for mineral uptake

• Important Symbiotic Relationships

– Rhizobiumbacteria live in root nodules

• Bacteria fix atmospheric nitrogen

• Host plant provides the bacteria with carbohydrates

– Mycorrhizal association between fungi and plant roots

• Fungus increases the surface area for water and mineral uptake and break down organic matter

• Root provides the fungus with sugars and amino acids

• Parasitic plants • Carnivorous plants

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Root Nodules

Portion of infected cell root nodule

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Mycorrhizae

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Mycorrhizae present

Mycorrhizae not present

mycorrhizae

(Top): © B. Runk/S. Schoenberger/Grant Heilman Photography; (Circle): © Dana Richter/Visuals Unlimited

Other Ways to Acquire Nutrition

bulbs release digestive enzymes dodder

(brown)

Sundew leaf enfolds prey

sticky hairs narrow leaf form

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25.3 Transport Mechanisms in

Plants

• Vascular tissues transport water and nutrients

 Xylem transports water and minerals • Two types of conducting cells

– Tracheids – Vessel elements

• Water flows passively from an area of higher water potential to an area of lower water potential



Phloem

transports organic materials

• Conducting cells are sieve-tube members

– Have companion cells to provide proteins – End walls are sieve plates

– Plasmodesmata extend through sieve plates

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38

stoma

sugar

sugar Stem phloem

phloem xylem

xylem

Root Leaf

H2O

CO2

O2

H2O CO2

O2

intercellular spaces

Plant Transport System

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Transport Mechanisms in Plants

• Potential energy is stored energy

• Water potential

is the energy of water.

– Water moves from a region of higher potential

to a region of lower potential

• In terms of cells, two factors usually

determine water potential:

– Water pressure across a membrane

– Solute concentration across a membrane

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The Concept of Water Potential

• Pressure potential

is the effect that pressure has

on water potential.

 Water moves across a membrane from the area of higher pressure to the area of lower pressure.

 The higher the water pressure, the higher the water potential.

• Osmotic potential

takes into account the

presence of solutes

 Water tends to move from the area of lower solute concentration to the area of higher solute

concentration.

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Water Potential and Turgor

Pressure

41

lo

w

e

r

h

ig

h

e

r

Extracellular fluid:

a. Plant cells need water. Inside the cell:

H2O

enters the cell

b. Plant cells are turgid. Pressure potential increases until the cell is turgid Equal water potential inside and outside the cell cell wall

central vacuole Wilted Turgid

cell wall

central vacuole

water potential pressure potential osmotic potential water potential pressure potential osmotic potential

Transport Mechanisms in Plants

• Water Transport

– Xylem vessels form an open pipeline

• The vessel elements are separated by perforated plates

• Water moves into and out of tracheids through pits

– Water entering roots creates a positive

pressure (

root pressure

)

• Pushes xylem sap upward

– May be responsible for guttation

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Conducting Cells of Xylem

43

a. Perforation plate with a single, large opening b. Perforation plate with a series of openings 20 mm

pits

20 mm 50 mm

c. Tracheids

a, b: Courtesy Wilfred A. Cote, from H.A. Core, W.A. Cote, and A.C. Day, Wood: Structure and Identification2/e; c: Courtesy W.A. Cote, Jr., N.C. Brown Center for Ultrastructure Studies, SUNY-ESF

Guttation

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Transport Mechanisms in Plants

• Cohesion-tension model

of xylem

transport suggests a passive xylem

transport

–

Cohesion

is the tendency of water molecules

to cling together

–

Adhesion

is the ability of the polar water

molecules to interact with molecules of vessel

walls

– A continuous

water column

moves passively

upward due to

transpiration

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Transport Mechanisms in Plants

• Leaves

– Transpiration causes water loss through stomata – Water molecules that evaporate are replaced by water

molecules from leaf veins

– Due to cohesion,transpiration exerts a pulling force (tension) drawing water through the xylem to the leaf cells

– Waxy cuticle prevents water loss when stomata are closed

• Stem

– Tension in xylem pulls the water column upward • Roots

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47

H2O

stoma

xylem cell wall

water molecule

xylem water molecule

root hair Leaves

Roots Stem

mesophyll cells

intercellular space xylem in

leaf vein

• Transpiration creates tension. • Tension pulls the water

column upward from the roots to the leaves.

cohesion by hydrogen bonding between water molecules

adhesion due to polarity of water molecules

• Cohesion makes water continuous. • Adhesion keeps water

column in place.

• Water enters xylem at root. • Water column extends

from leaves to the root.

H2O

Transport Mechanisms in Plants

• Opening and Closing of Stomata:

– Each stoma in leaf epidermis is bordered by

guard cells

• Increased turgor pressure in guard cells opens stoma

• Active transport of K+_{into guard cells causes water}

to enter by osmosis and stomata to open

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Opening and Closing of Stomata

49

Closed stoma

K+

a.

b. 25 µm

25 µm

Open Stoma

H2O H2O

H+

K+

vacuole guard cell

H2O

K+exits guard cells, and water follows. H2O

K+_{enters guard cells, and water follows.}

stoma

Transport Mechanisms in Plants

• Organic Nutrient Transport:

– Role of phloem

• Phloem transports sugar

• Girdling of tree below the level of leaves causes bark to swell just above the cut

– Sugar accumulates in the swollen tissue • Radioactive tracer studies confirm that phloem

transports organic nutrients

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51

a. An aphid feeding on a plant stem

Transport Mechanisms in Plants

• Pressure-Flow Model

of Phloem Transport

– Sieve tubes form a continuous pathway for organic nutrient transport

• Sieve-tube members are aligned end to end • Strands of plasmodesmata extend through sieve

plates between sieve-tube members

– Positive pressure drives the movement of sap in sieve tubes

• Sucrose is actively transported into phloem at the leaves

• Water follows by osmosis, creating positive pressure

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Pressure-Flow Model of Phloem Transport

53

mesophyll cell of leaf

Leaf

phloem xylem water sugar

phloem xylem

Root • Sugar is stored in

the sink. • Cells can use it for

cellular respiration. • Water exits by

osmosis and returns to the xylem. • Phloem contents flow

from a source to a sink. • Xylem flows from the

roots to the leaves.

Roots Stems Leaves • Leaves are the main

source of sugar production. • Sugar (pink) is actively

transported into sieve tubes. • Water (blue) follows

by osmosis.

cortex cell of root