PLANTS - The Bio Edge · 2020. 2. 17. · Transpiration, the loss of water from leaves (mostly...

PLANTSSTRUCTURE AND FUNCTION

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Three basic organs evolved: roots, stems, and leaves

• They are organized into a root system and a shoot system

Reproductive shoot (flower)

Terminal bud

Node

Internode

Terminal bud

Vegetative shoot

Blade Petiole

Stem

Leaf

Taproot

Lateral roots Root system

Shoot system

Axillary bud

STRUCTURETissues & Organs


ROOTS

• A root – Is an organ that anchors the vascular plant – Absorbs minerals and water – Often stores organic nutrients


Roots

• In most plants – The absorption of water and minerals occurs near

the root tips, where vast numbers of tiny root hairs increase the surface area of the root


• Many plants have modified roots

(a) Prop roots (b) Storage roots (c) “Strangling” aerialroots

(d) Buttress roots (e) Pneumatophores


Stems

• A stem is an organ consisting of – An alternating system of nodes, the points at which

leaves are attached – Internodes, the stem segments between nodes


Stems

• Many plants have modified stems

Rhizomes. The edible base of this ginger plant is an example of a rhizome, a horizontal stem that grows just below the surface or emerges and grows along the surface.

(d)

Tubers. Tubers, such as these red potatoes, are enlarged ends of rhizomes specialized for storing food. The “eyes” arranged in a spiral pattern around a potato are clusters of axillary buds that mark the nodes.

(c)Bulbs. Bulbs are vertical, underground shoots consisting mostly of the enlarged bases of leaves that store food. You can see the many layers of modified leaves attached to the short stem by slicing an onion bulb lengthwise.

(b)

Stolons. Shown here on a strawberry plant, stolons are horizontal stems that grow along the surface. These “runners” enable a plant to reproduce asexually, as plantlets form at nodes along each runner.

(a)

Storage leaves

Stem

Root Node

Rhizome

Root


Leaves

• The leaf – Is the main photosynthetic organ of most vascular

plants


Leaves

• Some plant species – Have

evolved modified leaves that serve various functions

(a) Tendrils. The tendrils by which thispea plant clings to a support are modified leaves. After it has “lassoed” a support, a tendril forms a coil that brings the plant closer to the support. Tendrils are typically modified leaves, but some tendrils are modified stems, as in grapevines.

(b) Spines. The spines of cacti, such as this prickly pear, are actually leaves, and photosynthesis is carried out mainly by the fleshy green stems.

(c) Storage leaves. Most succulents, such as this ice plant, have leaves modified for storing water.

(d) Bracts. Red parts of the poinsettia are often mistaken for petals but are actually modified leaves called bracts that surround a group of flowers. Such brightly colored leaves attract pollinators.

(e) Reproductive leaves. The leaves of some succulents, such as Kalanchoe daigremontiana, produce adventitious plantlets, which fall off the leaf and take root in the soil.


The Three Tissue Systems: Dermal, Vascular, and Ground

• Each plant organ – Has dermal,

vascular, and ground tissues

Dermal tissue

Ground tissue Vascular

tissue


• The dermal tissue system – Consists of the epidermis and periderm

• The vascular tissue system – Carries out long-distance transport of materials

between roots and shoots – Consists of two tissues, xylem and phloem

• Ground tissue – Includes various cells specialized for functions

such as storage, photosynthesis, and support


Vascular Tissue (side note)• Xylem

– Conveys water and dissolved minerals upward from roots into the shoots

• Phloem – Transports organic nutrients from where they are made to

where they are neededWATER-CONDUCTING CELLS OF THE XYLEM

Vessel Tracheids 100 µm

Tracheids and vessels

Vessel element

Vessel elements with partially perforated end walls

Pits

Tracheids

SUGAR-CONDUCTING CELLS OF THE PHLOEM

Companion cell

Sieve-tube member

Sieve-tube members: longitudinal view

Sieve plate

Nucleus

CytoplasmCompanion cell

30 µm

15 µm


Meristems

• Lateral meristems – Add thickness to woody plants through secondary

growth

• Meristems generate cells for new organs • Apical meristems

– Are located at the tips of roots and in the buds of shoots

– Elongate shoots and roots through primary growth


Meristems

• An overview of primary and secondary growth

In woody plants, there are lateral meristems that add secondary

growth, increasing the girth of

roots and stems.

Apical meristems add primary growth, or growth in length.

Shoot apical meristems (in buds)


Primary Growth

• Primary growth lengthens roots and shoots

• Primary growth produces the primary plant body, the parts of the root and shoot systems produced by apical meristems

• The root tip is covered by a root cap, which protects the delicate apical meristem as the root pushes through soil during primary growth


Primary Growth of Roots

Dermal

Ground

Vascular

Key

Cortex Vascular cylinder

Epidermis

Root hairZone of maturation

Zone of elongation

Zone of cell division

Apical meristem

Root cap

100 µm


Secondary Growth

• Secondary growth adds girth to stems and roots in woody plants

• Secondary growth – Occurs in stems and roots of woody plants but

rarely in leaves

• The secondary plant body – Consists of the tissues produced by the vascular

cambium and cork cambium


The Vascular Cambium and Secondary Vascular Tissue

• The vascular cambium – Is a cylinder of meristematic cells one cell thick

Secondary phloem

Vascular cambiumLate wood

Early woodSecondary xylem

Cork cambium

Cork

(b) Transverse sectionof a three-year-old stem (LM)

Bark

0.5 mm0.5 mm


Growth ring

Heartwood

Sapwood

Vascular cambium

Secondary phloem

Layers of periderm

Secondary xylem

Bark


Key to labels

DermalGround

Vascular

Guard cells

Stomatal pore

Epidermal cell

50 µmSurface view of a spiderwort (Tradescantia) leaf (LM)

(b)Cuticle

Sclerenchyma fibers

Stoma

Upper epidermis

Palisade mesophyll

Spongy mesophyll

Lower epidermis

Cuticle

Vein

Guard cells

Xylem

Phloem

Guard cells

Bundle- sheath cell

Cutaway drawing of leaf tissues(a)

Vein Air spaces Guard cells

100 µmTransverse section of a lilac (Syringa) leaf (LM)

(c)

Leaf Anatomy

FUNCTIONTransport in Vascular Tissue


Vascular Tissue– Transports nutrients throughout a plant; such

transport may occur over long distances


MineralsH2O CO2

O2

CO2 O2

H2O Sugar

Light

Transport

• A variety of physical processes – Are involved in the different types of transport

Sugars are produced by photosynthesis in the leaves.5

Sugars are transported as phloem sap to roots and other parts of the plant.

6

Through stomata, leaves take in CO2 and expel O2. The CO2 provides carbon for photosynthesis. Some O2 produced by photosynthesis is used in cellular respiration.

4

Transpiration, the loss of water from leaves (mostly through

stomata), creates a force within leaves that pulls xylem sap upward.

3

Water and minerals are transported upward from

roots to shoots as xylem sap.

2

Roots absorb water and dissolved minerals

from the soil.

1 Roots exchange gases with the air spaces of soil, taking in O2 and discharging CO2. In cellular respiration, O2 supports the breakdown of sugars.

7


The Importance of Photosynthesis: A Review

Light reactions: • Are carried out by molecules in the thylakoid membranes • Convert light energy to the chemical energy of ATP and NADPH • Split H2O and release O2 to the atmosphere

Calvin cycle reactions: • Take place in the stroma • Use ATP and NADPH to convert CO2 to the sugar G3P • Return ADP, inorganic phosphate, and NADP+ to the light reactions

O2

CO2H2O

Light

Light reaction Calvin cycle

NADP+

ADP

ATP

NADPH

+ P 1

RuBP 3-Phosphoglycerate

Amino acids Fatty acids

Starch (storage)

Sucrose (export)

G3P

Photosystem II Electron transport chain

Photosystem I

Chloroplast


Roots

• Roots are primarily anchors for the plant!

• Roots absorb water and minerals from the soil

• Water and mineral salts from the soil – Enter the plant through the epidermis of roots and

ultimately flow to the shoot system

• Much of the absorption of water and minerals occurs near root tips, where the epidermis is permeable to water and where root hairs are located

• Root hairs account for much of the surface area of roots


Symbiosis• Most plants form mutually beneficial relationships with fungi,

which facilitate the absorption of water and minerals from the soil

• Roots and fungi form mycorrhizae, symbiotic structures consisting of plant roots united with fungal hyphae

2.5 mm


Transpiration Cohesion Mechanism

• Ascent of xylem sapXylem sapOutside air Ψ

= –100.0 MPa

Leaf Ψ (air spaces) = –7.0 MPa

Leaf Ψ (cell walls) = –1.0 MPa

Trunk xylem Ψ = – 0.8 MPa

Wat

er p

oten

tial g

radi

ent

Root xylem Ψ = – 0.6 MPa

Soil Ψ = – 0.3 MPa

Mesophyll cells

Stoma

Water molecule

Atmosphere

Transpiration

Xylem cells Adhesion Cell

wall

Cohesion, by hydrogen bonding

Water molecule

Root hair

Soil particle

Water

Cohesion and adhesion in the xylem

Water uptake from soil


Stomata

• Stomata help regulate the rate of transpiration

• Leaves generally have broad surface areas – And high surface-to-volume ratios

• About 90% of the water a plant loses – Escapes through stomata


Stomata

• Both of these characteristics – Increase photosynthesis – Increase water loss through stomata

20 µm


Moving Phloem Sap

• Organic nutrients are translocated through the phloem

• Translocation – Is the transport of organic nutrients in the plant

• Phloem sap – Is an aqueous solution that is mostly sucrose – Travels from a sugar source to a sugar sink


• A sugar source – Is a plant organ that is a net producer of sugar,

such as mature leaves

• A sugar sink – Is an organ that is a net consumer or storer of

sugar, such as a tuber or bulb

Movement from Sugar Sources to Sugar Sinks

NUTRITIONTransport in Vascular Tissue


Overview

• Every organism – Continually exchanges energy and materials with

its environment

• Plants require certain chemical elements to complete their life cycle

• Plants derive most of their organic mass from the CO2 of air – But they also depend on soil nutrients such as water

and minerals


CO2, the source of carbon for

Photosynthesis, diffuses into

leaves from the air through

stomata.

Through stomata, leaves expel H2O and O2.

H2O

O2

CO2

Roots take in O2 and expel CO2. The plant uses O2 for cellular respiration but is a net O2 producer.

O2

CO2

H2O

Roots absorb H2O and

minerals from the soil.

Minerals


Macronutrients and Micronutrients

• More than 50 chemical elements – Have been identified among the inorganic

substances in plants, but not all of these are essential

• A chemical element is considered essential – If it is required for a plant to complete a life cycle


Soil• Soil quality is a major determinant of plant distribution

and growth • Along with climate

– The major factors determining whether particular plants can grow well in a certain location are the texture and composition of the soil

• Texture – Is the soil’s general structure

• Composition – Refers to the soil’s organic and inorganic chemical

components


Nutritional Deficiencies

• Nitrogen is often the mineral that has the greatest effect on plant growth

• Plants require nitrogen as a component of – Proteins, nucleic acids, chlorophyll, and other

important organic molecules


Soil Bacteria and Nitrogen Availability

• Nitrogen-fixing bacteria convert atmospheric N2

– To nitrogenous minerals that plants can absorb as a nitrogen source for organic synthesis

Atmosphere

N2

Soil

N2 N2

Nitrogen-fixingbacteria

Organicmaterial (humus)

NH3 (ammonia)

NH4+

(ammonium)

H+

(From soil)

NO3–

(nitrate)Nitrifying bacteria

Denitrifyingbacteria

Root

NH4+

Soil

Atmosphere

Nitrate and nitrogenous

organiccompoundsexported in

xylem to shoot system

Ammonifyingbacteria


Nutritional Adaptations

• Plant nutritional adaptations often involve relationships with other organisms

• Two types of relationships plants have with other organisms are mutualistic – Symbiotic nitrogen fixation – Mycorrhizae


The Role of Bacteria in Symbiotic Nitrogen Fixation

• Symbiotic relationships with nitrogen-fixing bacteria – Provide some plant species with a built-in source

of fixed nitrogen

• From an agricultural standpoint – The most important and efficient symbioses

between plants and nitrogen-fixing bacteria occur in the legume family (peas, beans, and other similar plants)


Legumes• Along a legumes possessive roots are swellings

called nodules – Composed of plant cells that have been “infected” by

nitrogen-fixing Rhizobium bacteria

(a) Pea plant root. The bumps on this pea plant root are nodules containing Rhizobium bacteria.The bacteria fix nitrogen and obtain photosynthetic products supplied by the plant.

Nodules

Roots


Mycorrhizae and Plant Nutrition• Mycorrhizae

– Are modified roots consisting of mutualistic associations of fungi and roots

• The fungus – Benefits from a steady supply of sugar donated by

the host plant

• In return, the fungus – Increases the surface area of water uptake and

mineral absorption and supplies water and minerals to the host plant


The Two Main Types of Mycorrhizae• In ectomycorrhizae

– The mycelium of the fungus forms a dense sheath over the surface of the root

Mantle (fungal sheath)

Epidermis Cortex Mantle (fungal sheath)

Endodermis

Fungal hyphaebetweencortical cells

(colorized SEM)

100 µm


The Two Main Types of Mycorrhizae

• In endomycorrhizae – Microscopic fungal hyphae extend into the root

Epidermis Cortex

Fungal hyphae

Roothair

10 µm

(LM, stained specimen)

Cortical cells

Endodermis

Vesicle

Casparianstrip

Arbuscules


Agricultural Importance of Mycorrhizae

• Farmers and foresters – Often inoculate seeds with spores of mycorrhizal

fungi to promote the formation of mycorrhizae


Epiphytes, Parasitic Plants, and Carnivorous Plants

• Some plants – Have nutritional adaptations that use other

organisms in nonmutualistic ways


• Exploring unusual nutritional adaptations in plants

Staghorn fern, an epiphyte

EPIPHYTES

PARASITIC PLANTS

CARNIVOROUS PLANTS

Mistletoe, a photosynthetic parasite Dodder, a nonphotosynthetic parasite

Host’s phloem

Haustoria

Indian pipe, a nonphotosynthetic parasite

Venus’ flytrapPitcher plants Sundews

Dodder

REPRODUCTIONAngiosperms


Sexual Reproduction in Plants• Angiosperms plants with seeds and flowers

• Pollination enables gametes to come together within a flower

• A dominant sporophyte stage – Produces spores that develop within flowers into male

gametophytes (pollen grains) – Produces female gametophytes (embryo sacs)


Life Cycle Animals

• In animals – Meiosis occurs

during gamete formation

– Gametes are the only haploid cells

Gametes

Diploid multicellular

organism

Key

MEIOSIS FERTILIZATION

n

n

n

2n2nZygote

Haploid

Diploid

Mitosis

(a) Animals


MEIOSIS FERTILIZATION

nn

n

nn

2n2n

Haploid multicellular organism (gametophyte)

Mitosis Mitosis

SporesGametes

Mitosis

Zygote

Diploid multicellular organism (sporophyte)

(b) Plants and some algae

• Plants and some algae – Exhibit an

alternation of generations

– The life cycle includes both diploid and haploid multicellular stages

Life Cycle Plants


Angiosperm Plants (90% of all plants on earth)

• An overview of angiosperm reproductionAnther at tip of stamen

Filament

AntherStamen

Pollen tube

Germinated pollen grain (n) (male gametophyte) on stigma of carpel

Ovary (base of carpel)

Ovule

Embryo sac (n) (female gametophyte)

FERTILIZATIONEgg (n)

Sperm (n)

PetalReceptacle

Sepal

Style

Ovary

Key

Haploid (n)Diploid (2n)

(a) An idealized flower.

(b) Simplified angiosperm life cycle. See Figure 30.10 for a more detailedversion of the life cycle, including meiosis.

Mature sporophyte plant (2n) with flowers

Seed (develops from ovule)

Zygote (2n)

Embryo (2n) (sporophyte)

Simple fruit (develops from ovary)

Germinating seed

Seed

CarpelStigma


Flower Structure

• Flowers – Are the reproductive shoots of the angiosperm

sporophyte – Are composed of four floral organs: sepals, petals,

stamens, and carpels


Seeds & Fruit

• After fertilization, ovules develop into seeds and ovaries into fruits


Double Fertilization

• In double fertilization – One sperm fertilizes the egg – The other sperm combines with the polar nuclei,

giving rise to the food-storing endosperm


From Ovule to Seed

• After double fertilization – Each ovule develops into a seed – The ovary develops into a fruit enclosing the

seed(s)


Endosperm Development

• Endosperm development – Usually precedes embryo development

• In most monocots and some eudicots – The endosperm stores nutrients that can be used

by the seedling after germination

• In other eudicots – The food reserves of the endosperm are

completely exported to the cotyledons


Structure of the Mature Seed

• The embryo and its food supply – Are enclosed by a hard, protective seed coat


• In a common garden bean, a eudicot – The embryo consists of the hypocotyl, radicle, and

thick cotyledons

(a) Common garden bean, a eudicot with thick cotyledons. The fleshy cotyledons store food absorbed from the endosperm before the seed germinates.

Seed coat

Radicle

Epicotyl

Hypocotyl

Cotyledons



• The seeds of other eudicots, such as castor beans – Have similar structures, but thin cotyledons

Seed coat

Endosperm

Cotyledons

Epicotyl

Hypocotyl

Radicle

Seed coat

Endosperm

Cotyledons

Epicotyl

Hypocotyl

Radicle



• The embryo of a monocot – Has a single cotyledon, a coleoptile, and a

coleorhiza

(c) Maize, a monocot. Like all monocots, maize has only one cotyledon. Maize and other grasses have a large cotyledon called a scutellum. The rudimentary shoot is sheathed in a structure called the coleoptile, and the coleorhiza covers the young root.

Scutellum (cotyledon)

Coleoptile

Coleorhiza

Pericarp fused with seed coat

Endosperm

Epicotyl

Hypocotyl

Radicle



From Ovary to Fruit

• A fruit – Develops from the ovary – Protects the enclosed seeds – Aids in the dispersal of seeds by wind or animals


Fruit Diversity

• Fruits are classified into several types – Depending on their developmental origin

Figure 38.9a–c

Simple fruit. A simple fruit develops from a single carpel (or several fused carpels) of one flower (examples: pea, lemon, peanut).

(a) Aggregate fruit. An aggregate fruit develops from many separate carpels of one flower (examples: raspberry, blackberry, strawberry).

(b) Multiple fruit. A multiple fruit develops from many carpels of many flowers (examples: pineapple, fig).

(c)Pineapple fruitRaspberry fruitPea fruit

Stamen

Carpel (fruitlet) Stigma

Ovary

Raspberry flower

Each segment develops from the carpel of one flower

Pineapple inflorescence

Stamen

CarpelsFlowerOvary

StigmaStamen

Ovule

Pea flower

Seed


Seed Germination

• As a seed matures – It dehydrates and enters a phase referred to as

dormancy


Seed Dormancy: Adaptation for Tough Times

• Seed dormancy – Increases the chances that germination will occur

at a time and place most advantageous to the seedling

• The breaking of seed dormancy – Often requires environmental cues, such as

temperature or lighting cues


From Seed to Seedling

• Germination of seeds depends on the physical process called imbibition – The uptake of water due to low water potential of

the dry seed


Foliage leaves

Cotyledon

Hypocotyl

Radicle

Epicotyl

Seed coat

Cotyledon

Hypocotyl Cotyledon

Hypocotyl

Common garden bean. In common garden beans, straightening of a hook in the hypocotyl pulls the cotyledons from the soil.

(a)

• The radicle – Is the first organ

to emerge from the germinating seed

• In many eudicots – A hook forms in

the hypocotyl, and growth pushes the hook above ground



• Monocots – Use a different

method for breaking ground when they germinate

• The coleoptile – Pushes upward

through the soil and into the air

Foliage leaves

ColeoptileColeoptile

Radicle

Maize. In maize and other grasses, the shoot grows straight up through the tube of the coleoptile.

(b)


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PLANTS - The Bio Edge · 2020. 2. 17. · Transpiration, the loss of water from leaves (mostly...

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