Bio 100 Chapter 21

Chapter 21Plant Organization and HomeostasisLecture Outline

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

21.1 Flowering plants typically have roots, stems, & leaves

Most flowering plants possess a shoot system & a root system

Shoot system – stem, branches, leaves, & flowers

Root system – main root and its branches

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21-3

Figure 21.1A, pg. 432 Organization of

a plant body

stem

internode

petiole

axillary bud

terminal bud

node

Shoot systemRoot system

node

leaf blade

root tip

vascular tissues(xylem and phloem)

lateralbranchrootroothairs

primaryroot


The Stem 4 main functions

Supports the leaves & flowers Growth of stem Transport of water & nutrients between leaves and roots Food storage

Terminal bud in shoot tip Produces new leaves and new axillary (lateral) buds Axillary buds can produce new branches or flowers

Node is where a leaf or flower joins the stem Internode is the region between the nodes

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21-5

Figure 21.1B, pg. 433: Modified leaves adapt to a plant’s environment

stem

leaves

Spines are the leaves of a cactus© Patti Murray/Animals Animals


Leaves Usually the primary organs of photosynthesis

Blade – wide portion of a foliage leaf

Petiole – stalk that attaches the blade to the stem

Examples of modified leaves:

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Figure 21.1B Modified leaves adapt to a plant’s environment (Cont.)

tendril

Tendrils are modified leaves of a cucumber© Michael Gadomski/Photo Researchers, Inc


21-8

Figure 21.1B Modified leaves adapt to a plant’s environment (Cont.)

Leaves of a Venus flytrap capture insects© Steven P. Lynch


Roots Main functions

1. Anchor plant in soil

2. Absorb water & minerals from soil

3. Produce hormones

4. Some also store food

Root hairs increase surface-to-volume ratio

Tap roots vs. fibrous roots

Examples of each type of root system:21-9

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Figure 21.1C Taproot system (left) versus fibrous root system (right)

(taproot): © Jonathan Buckley/Getty Images;; (fibrous root): © The McGraw-hill companies Inc./Evelyn Jo Johnson, photographer


Taproot Fibroous root system

21.2 Flowering plants are either monocots or eudicots

Monocots have one cotyledon Root vascular tissue rings pith Vascular bundles scattered in stem Leaf veins are parallel Flower parts in multiples of three

Eudicots have two cotyledons Root phloem between areas of xylem Vascular bundles in a distinct ring Leaf veins form a net pattern Flower parts in multiples of four or five 21-11

21-12

Figure 21.2, pg. 434 Monocots & eudicots are structurally different


Mo

no

cots

Eu

dic

ots

Two cotyledons in seedRoot phloem between

arms of xylemVascular bundlesin a distinct ring

Leaf veins forma net pattern

Flower parts in fours orfives and their multiples

axillary bud

pith

xylem

phloem

One cotyledon in seed

xylem

Seed Root Stem Leaf Flower

endosperm phloempith

Root xylem andphloem in a ring

Vascular bundlesscattered in stem

axillary bud

Flower parts in threesand multiples of three

Leaf veins forma parallel pattern

HOW BIOLOGY IMPACTS OUR LIVES

21.3 Monocots serve humans well

Although the monocots are a small group compared to the eudicots, they have great importance

Domestication of monocot plants included selective breeding in order to accumulate certain desirable traits in crops

Corn is by far the most important crop plant in the United States

Over 50% of the world’s people depend on rice for about 80% of their calorie requirements

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21-14

Figure 21A, pg. 435 Monocot variety


(rice plants): © Corbis RF; (rice grain head): © Dex Image/Getty RF; (wheat): © Earl Roberge/Photo Researchers, Inc

Rice plants, Oryza

grain head

grain head

Wheat plants,Triticum

21-15

Figure 21A Monocot variety (Cont.)


(ear of corn): © Doug Wilson/Corbis; (corn plants): © Adam Hart-Davis/SPL/Photo Researchers, Inc.; (barley plants): © Sundell Larsen/Getty RF; (barley grains): © C.

Sherburne/Photolink/Getty RF

Corn plants, Zea Barley

ear

21.3 Plants have specialized cells & tissues

Apical meristem Located in the terminal bud of the shoot

system and in the root tip

Daughter cells differentiate into 1 of 3 primary meristems

1. Epidermal tissue forms the outer protective covering of a plant

2. Ground tissue fills the interior of a plant and serves metabolic functions

3. Vascular tissue contains xylem and phloem21-16

21-17

Figure 21.1A, pg. 432 Organization of

a plant body

stem

internode

petiole

axillary bud

terminal bud

node

Shoot systemRoot system

node

leaf blade

root tip

vascular tissues(xylem and phloem)

lateralbranchrootroothairs

primaryroot


Epidermal Tissue

Epidermis covers entire body of plant

Waxy cuticle minimizes water loss

Leaves contains stomata ringed by guard cells

Roots have root hairs

Epidermis is replaced by cork in tree trunkNew cork cells are made by cork cambium

21-18

Figure 21.3A, pg. 436 Modifications of epidermal tissue


b: © Runk/Schoenberger/Grant Heilman Photography

b. Root hairs

corn seedling

elongating root tip

roothairs

guard cell chloroplasts

epidermalcell

nucleusstoma

a. Stoma of leaf


a: © J.R. Waaland/Biological Photo Service

21-20

Figure 21.3A Modifications of epidermal tissue (Cont.)


c: © Kingsley Stern

c. Cork of older stem 20 m

corkcork cambium

lenticel periderm

Ground Tissue Bulk of stems, leaves, and roots

Contains three types of cells Parenchyma cells – the least specialized of the

cell types and are found in all the organs of a plant Collenchyma cells have thicker primary walls

than parenchyma cells Provide structural support in nonwoody plants, especially

in areas of elongation Sclerenchyma cells have thick secondary cell

walls impregnated with lignin Makes plant cell walls tough and hard, in areas where

growth has stopped elongation

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21-22

Figure 21.3B, pg. 436 Ground

tissue cells


(all): © Biophoto Associates/Photo Researchers, Inc

Parenchyma cells with thin walls

50 m 50 m

50 m

Collenchyma cellswith thicker walls

Sclerenchyma cellswith very thick walls

Vascular Tissue

Xylem Transports water and minerals from roots to leaves Contains vessel elements (thicker) & tracheids (thinner)

Phloem Transports sugar, in the form of sucrose, and other organic

compounds, such as hormones, from the leaves to the roots Sieve-tube members – conducting cells of phloem are

arranged to form a continuous sieve tube Companion cells – nucleated cells

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Figure 21.3C, pg. 437 Xylem structure

a. Xylem micrograph

pits

tracheids

tracheid

end wall

50 m c.Tracheids

pittedwalls

vesselelement

b.Two types of vessels

xylemparenchymacell

vesselelement

(Left): © J.R. Waaland/Biological Photo Service


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Figure 21.3D, pg. 437 Phloem structure


Sieve-tube member and companion cellsPhloem micrograph

companion cell

sieve plate

companion cell

sieve plate

nucleus

phloemparenchyma cell

sieve-tubemember

sieve-tubemember

20 µm

(Left): © George Wilder/Visuals Unlimited

21.4 The three types of plant tissues are present in each organ

Leaf Upper and lower epidermis has an outer, waxy

cuticle, which prevents water loss Stomata located in lower epidermis

Interior of a leaf is made of mesophyll, Ground tissue composed of parenchyma cells Contain chloroplasts and carry on photosynthesis Palisade (tightly packed, elongated cells) vs spongy

mesophyll (irregular cells bounded by air spaces right next to the stomata)

Leaf veins branch and terminate in the mesophyll

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a. Leaf

stoma

guard cell

xylem

phloemleaf vein

mesophyll

cuticle

lowerepidermis

upperepidermis

Xylem transportswater and minerals.

Phloem transports sugar.

Stem

Herbaceous plants have “nonwoody” stems

Ground tissue consists of cortex and central pith Vascular bundles

Ring in eudicot Scattered in monocot

Vascular tissue supports shoot system and transport food and water

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Figure 21.4B Internal structure of the leaf,

stem, and rootCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

100 µm

cortex

pith

epidermisepidermis

b. Eudicot stem c. Monocot stem

cortex

vascularbundle

vascularbundle

b: © Ed Reschke; c: © CABISCO/Phototake;

epidermal

ground

vascular

Tissue Types

Root

Epidermis usually consists of only a single layer of cells and many epidermal cells have root hairs

Large, thin-walled parenchyma cells make up the cortex, the layer of ground tissue cells located beneath the epidermis

Cells contain starch granules, and the cortex functions in food storage

21-30

endodermis

epidermis

phloem

xylem

cortex

All tissues

50 µmepidermalgroundvascular d. Eudicot root

Tissue Types

vascularcylinder

Vascular cylinder

21-32

Figure 21.4A , pg. 438 Arrangement of plant

tissues in the organs of eudicots


Stem

Leaf

Root

groundtissue

epidermaltissuevasculartissue

groundtissue

groundtissue

epidermaltissue

vasculartissue

vasculartissue

epidermaltissue

21-33

Figure 21.4B Internal structure of the leaf,

stem, and root


vascular tissue

100 µm

cortex

pith

epidermisepidermis

b. Eudicot stem

a. Leaf

c. Monocot stem

cortex

stoma

guard cell

xylem

phloemleaf vein

mesophyll

cuticle

endodermis

epidermis

phloem

xylem

cortex

All tissues

50 µmepidermalgroundvascular d. Eudicot root

epidermaltissue

groundtissue

shoot systemroot system

Tissue Types

vascularcylinder

Vascular cylinder

vascularbundle

vascularbundle

lowerepidermis

upperepidermis

Xylem transportswater and minerals.

Phloem transports sugar.

b: © Ed Reschke; c: © CABISCO/Phototake; d: © CABISCO/Phototake

21.5 Primary growth lengthens the root & shoot systems

Primary growth

Causes a plant to grow lengthwise

Centered in the apex (tip) of the shoot and of the root

Meristem is a region of actively dividing cells

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Root System

Zone of cell division

Protected by the root cap

Contains the root apical meristem

21-35

Root System

Zone of elongation Region where the root increases in length due to

elongation of cells Cells lengthen but are not fully specialized

Zone of maturation Region that does contain fully differentiated cells Recognized by root hairs

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21-37


(Right): Courtesy Ray F. Evert/University of Wisconsin Madison

endodermis

phloem

xylem

cortexepidermis

root hair

Root cap

a. b.

root cap

protoderm

procambium

pericycle

Zone ofelongation

Vascularcylinder

Zone ofcell division

groundmeristem

Zone ofmaturation

Root apical meristemprotected by

root cap

Figure 21.5A , pg. 440Cells within a eudicot

root tip

Shoot System

Shoot apical meristem produces everything

Leaves, axillary buds (can develop into stems or flowers), additional stem and sometimes flowers

Gives rise to the same primary meristems as in the root Protoderm → becomes epidermis of stems and leaves Ground mersitem → become cortex, pith, and mesophyll Procambium → vascular tissue (xylem and phloem)

Vascular cambium responsible for secondary growth (growing wider)

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21-39

Figure 21.5B, pg. 441 Shoot apical meristem


© J.R. Waaland/Biological Photo Service

leaf primordium

shoot apicalmeristem

protoderm

groundmeristem

procambium

epidermis

cortex

auxillary bud

vascularcambium

xylem

phloem

internode

Shoot System – Ex: Winter Twig

Terminal bud contains the apical meristem and leaf primordia of the shoot tip protected by terminal bud scales

Leaf scars and vascular bundle scars mark spot of abscission (dropoff)

Determine age of a stem by counting terminal bud scale scars because there is one for each year’s growth

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21-41

Figure 21.5C, pg. 441 Winter twig showing stem organization


axillary bud

Twig during winter

Twig during spring

leaf scar terminal bud

vascular bundlescars

terminal budscales

terminal budscale scar

Secondary Plant Growth

Secondary growth occurs only in woody plants Increases the girth (or width) of trunks, stems,

branches, and roots Occurs due to the growth of lateral meristems:

vascular cambium and cork cambium Woody stem has 3 distinct areas

Bark, wood, and pith Wood is actually secondary xylem that builds up year

after year

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21-43

Figure 21.6A, pg. 442 In a tree, vascular cambium

produces secondary xylem and phloem each year


epidermis

lenticel

primary phloem

primary xylem

primary xylem

secondary xylem

Bark: Includes periderm and also phloem

xylem ray

phloem ray

cork cambium

secondary phloemprimary phloem

cork

pith

1

2

3

primary xylemsecondary xylemvascular cambiumsecondary phloemprimary phloemcork cambiumcork

cortex

Vascular cambium:Lateral meristem that willproduce secondary xylemand secondary phloem ineach succeeding year.

Wood: Increases each year; includes annualrings of xylem

Pith: Parenchyma cells that have astorage function; becomessqueezed out by heartwood

Bark Contains periderm and phloem

Periderm is a secondary growth tissue that contains cork and cork cambium

Cork cambium lies beneath the epidermis, but later it is part of the periderm, which replaces epidermis

Cork cambium divides and produces the cork cells that disrupt and replace the epidermis

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Figure 21.6B, pg. 442 Heartwood has no transport function and servesas a depository for various substances such as resins and tannin.


cork

sapwood

heartwood

phloem

Bark

vascularcambium

Wood

21.7 Leaves are organized to carry on photosynthesis

Functions of a foliage leaf Carry on photosynthesis, regulate water loss,

and be protective against parasites and predators

Epidermal tissue on upper and lower surfaces Waxy cuticle to prevent water loss Stomata all CO2 gain and water loss

21-46

Mesophyll Elongated cells of the palisade mesophyll carry on

most of the photosynthesis Loosely packed spongy mesophyll increases the

amount of surface area for CO2 gain and water loss

Leaf veins Bring water and minerals to leaves and distribute

products of photosynthesis to other parts of plant Bundle sheaths – layers of cells surrounding

vascular tissue

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Figure 21.7, pg. 444 Leaf anatomyCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

guard cell

cuticle

cuticle

trihome

stoma

lower epidermis

leaf vein

air space

upper epidermis

blade

petiole

100 µm

nucleus

chloroplast

mitochondrion

central vacuole

Leaf cell Stoma and guard cells SEM of leaf

epidermal cell

nucleus

stoma

chloroplast

leaf vein

axillarybud

Water and mineralsenter leaf through xylem.

Sugar exits leafthrough phloem.

O2 and H O2

exit leafthrough stoma.

CO2 enters leafthrough stoma.

lowerepidermis

spongymesophyll

palisademesophyll

upperepidermis

spongymesophyll

palisademesophyll

bundle sheath cell

© Jeremy Burgess/SPL/Photo Researchers, Inc

21.8 Various mechanisms help plants maintain homeostasis

Anatomy of plants allows photosynthesis to occur Vascular tissue (xylem and phloem) brings water and

minerals CO2 from stomata Exposure to solar energy

Products of photosynthesis maintains homeostasis (constancy of the internal environment)

Epidermis protects plants from invasion Closing stomata prevents water loss

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Figure 21.8A, pg. 445 The organization of plants is conducive to maintaining homeostasis


stoma

leafvein

palisademesophyll

upperepidermis

vasculartissues

lowerepidermis

spongymesophyll

(Middle): Courtesy Ray F. Evert/University of Wisconsin Madison

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Figure 21.8B Stomata open (left) and close (right) according to water availability


25 µmStoma open 25 µmStoma closed© jeremy Burgess/SPL/Photo Researchers, Inc.

Phloem transport Source (where there are abundant sugar or carbohydrates) to sink (where

extra sugar or carbohydrates are needed) transport

Plant hormones Highly specific chemical signals between plant parts and cells Tropism is a growth response toward or away from a particular

stimulus

Examples: if in dark place, grow towards light

Defense Mechanisms Cuticle, epidermal projections, chemical toxins

Mutualistic relationship of plant roots and fungi Increase surface area by which roots absorb water and minerals

from soil, give fungi carbohydrates

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Figure 21.8C, pg. 446 Homeostatic mechanismsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

sun

immature leaf

plant cells

dead cell

living cell

mature leaf

sugar

pathogenicmicrobialattack

a. Phloem transports sugar to areas of need.

b. Hormones cause plants to bend toward the light.

d. Plants practice local cell death as a defense against attack.

c. Plant roots associate with fungi to acquire minerals.

C: © D. H. Marx/Visuals Unlimited

Connecting the Concepts:Chapter 21

Flowering plants are adapted to living on land Prevention of water loss is critical for land plants

Stomata and cork

On land, plants had to evolve a way to oppose the force of gravity Sclerenchyma cells, tracheids, and vessel elements. Secondary growth

Means of water uptake and transport Root hairs, xylem

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Bio 100 Chapter 21

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