pgb plant hormones gsbtm final

8/2/2019 PGB Plant Hormones GSBTM Final

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Click to edit Master subtitle style

4/23/12

Plant HormonesTranslocationTranspiration

andTropic Movements

Ms.Praveena G. Bhandari,Shri M. and N. Virani Science College,

Rajkot.


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Hormone = Gr. to excite

1) active in small amounts2) produced in one part of plant (i.e.source)

& transported to another for action(i.e.target)

3) action is specific for that siteCause physiological or developmental

responses (stimulatory or inhibitory)

Plant Hormones


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Depending on site of actionDevelopmental stage of plantConcentration of hormone

Each has a Multiplicity of

Effects


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Auxins(cell elongation) Gibberellins(cell elongation + cell division

translated into growth) Cytokinins(cell division + inhibits senescence) Abscisic acid(abscission of leaves and fruits +

dormancy induction of buds and seeds) Ethylene(promotes senescence, epinasty, and

fruit ripening)

General plant hormones


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Auxin


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Stimulate cell elongation-Bend toward light because more auxin remains

in cells on opposite side of light source Etiolated plants have long internodes because

auxin not quickly broken down Promotes apical dominance Pinching bud removes source of auxin and

releases axillary buds from apicaldominance Promotes growth of adventitious roots

Action of auxins


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Loosening of cell wall


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Action of auxins

Auxin concentration determines ifaction is stimulatory or inhibitory

Low concentration promotesadventitious root growth, but highconcentration inhibits root growth ofcuttings

2, 4-D is used as herbicide by applyingat high concentrations


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Gibberellin


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Discovered in association with Foolishdisease of rice (Gibberella fujikuroi)

infect

ed

uninfect

ed


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Types of gibberellins used in horticulture Several different gibberellins (GA) produced by

plants Large, complicated molecules not synthesized Commercial gibberellins produced by fungus

Site of gibberellin production inplants: Shoot and root tips (apical meristems)

Young, expanding leaves Embryos

Fruits Tubers

Gibberellins


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Stimulate cell elongation Dwarf plants treated with gibberellins produce

normal growth (Fig.)

Applied to grapes to elongate the peduncle (stem offlower cluster) and pedicels (stem of single flower),

making looser cluster (Fig.) Promotes cell division in vascularcambium

Promotes seed germination

Influences flower and fruitdevelopment

Action of gibberellins


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Dwarf pea plant treated withgibberellin


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Effect of Gibberellin


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Cytokinins


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Types of cytokinins used inhorticulture Several natural forms

Zeatin first cytokinin isolated Synthetic cytokinins used in horticulture:

Benzyladenine (BA) Site of cytokinin production in plants:

Embryos Young leaves and fruit

Apical meristems of roots

Cytokinins


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Actions of cytokinins in plants Promotes cell division (cytokinesis) Contributes to cell enlargement (in leaves) Stimulates differentiation of cells (with auxins)

High cytokinin and low auxin promotesshoot initiation in tissue culture,whereas reverse combination promotesroot formation

Moderate levels of both hormones

promotes callus growth

Delays senescence in leaves (maintains andpromotes synthesis of chlorophyll)

Function of cytokinins


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Ethylene

H H

\ /C = C

/ \

H H


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Ethylene

Gas at physiological temperatures Liquid form used in horticulture (ethephon)

Site of ethylene production in plants: Throughout plants

Actions of ethylene in plants

Inhibits root and shoot elongation by blockingtransport of auxins from apical meristems

Stimulates leaf curling (epinasty)


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Function of Ethylene Actions of ethylene in plants

Induces adventitious root formation by blocking(and accumulating) auxin at tip of stem cutting

Enhances flow of latex in rubber trees

Stimulates abscission of leaves and fruit

Used as a harvest aid for cherries

Promotes fruit ripening (apple, tomato, citrus,coffee)

Promotes senescence of flowers

Enhances flowering in pineapples


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Abscisic acid


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Abscisic acid

Similar structure as gibberellins Site of abscisic acid production in

plants: All organs (e.g. roots, leaves, stems, fruits) Actions of abscisic acid in plants

Counteracts effects of auxins and gibberellins Maintains dormancy in seeds and buds

Stimulates guard cells to close stomatas (toconserve water)

General growth

inhibitor

Produced in responseto stress


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Translocation

Transport in Plants


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Water and dissolved nutrients moveupwards from the roots.

Carbohydrates produced in leavesmove to rest of plant

Movement of carbohydrates through

vascular system is called

translocation.

Transport in plants


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How do plants transportcarbohydrates?

Carbohydrates produced in photosyntheticorgans (usually leaves) and often stored inroots.Movement of carbohydrates is through phloem

Phloem consists of two types ofcells:

Sieve cells: living cellsstacked on top of each other

Sieve-tube members:similar to sieve cells butfound only in angiosperms(flowering plants)


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Source and Sink

Source: where thesugar starts its

journey (eitherwhere it is produced

or stored).

Sink: where sugarends up (eitherwhere it is neededor will be stored).

Mass flow or pressure flow


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How do plants transport carbohydrates?

Mass-flow or pressure-flowhypothesis:


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Sap consists of sugar dissolved in water at highconcentrations: usually between 10% and 25%.

Since this is highly concentrated, plants haveto use active transport to work against adiffusion gradient as part of the sap-moving

process.

Sap


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This theory explains how sap moves ina plant from source to sink: Sugars begin at a source and are pumped

into phloem tube cells. Osmosis moves water into the cells and

raises pressure.

Pressure moves the sap.

Pressure-flow theory


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The leaf is a source ofsugar, since it makessugar byphotosynthesis.

Glucose and fructosemade by photosynthesisare linked to make

sucrose, which does notmove easily through thecell membranes.

Pressure-flow- 1


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Active transport isused to loadsucrose intophloem tubes

against a diffusiongradient. Assugar is loadedinto the cell, whatelse moves in onits own? What willhappen to thepressure in thecell?

Pressure-flow -2


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The highconcentration ofsucrose in the sieve

tube cells of thephloem causeswater to move inby osmosis, which

raises pressure inthe cell. Whathappens to thesap?

Pressure-flow -3


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A developing fruitis one example of asink. Sucrose maybe actively

transported out ofphloem into thefruit cells. In a root,sucrose is

converted intostarch, whichkeeps sugarmoving in by

diffusion.

Pressure-flow - 4


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As the sugarconcentrationdrops in thesieve tube cells,osmosis moveswater out of thetube.

Pressure-flow - 5


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As water movesout by osmosis,the pressure in thesieve tube cellsdrops. Thepressure differencealong the columnof sieve tube cellskeeps the sapflowing.

Pressure-flow - 6


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Pressure-flow Review

N t i t i d b


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Nutrients required byplants

Macronutrients (required in relatively largeamounts)

9 macronutrients including:

Nitrogen

Phosphorus

Potassium

7 micronutrients including:

Chlorine Iron

Manganese

Micronutrients (required in trace amounts)


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ExperimentIs suspected nutrient essential ?

T t i l t


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Nutrients required by plants

Transport in plants

Most nutrients needed by plants obtained fromsoil Most roots found in topsoil

Mineral particles (nutrients) Living organisms (particularly detritivores)

Humus (partly decayed organic matter)

Some plants in acidic bogs obtain Nitrogenby trapping and digesting insects (e.g.Venus flytrap)

Legumes house Nitrogen-fixing bacteria inroot nodules Most plants have mycorrhizal fungi that enhance

nutrient uptake by increasing surface area of roots

T t i l t


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How do plants get nutrients and water

into roots?

Transport in plants

Water absorbed by root hairs (projectionsof epidermis cells)

Root hairs greatly increase surface area

over which to absorb water Root hairs have greater osmotic potential

than soil

T t i l t


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How do plants get nutrients and water into

vascular system of roots?

Transport in plants

Water and ions enter root hairs and move betweenor through membranes of cells of cortex

Casparian strips block water movement; forcewater through cell membranes of endoderm

Endodermalcells selectsnutrientsthat enter

vasculartissue(xylem)

T t i l t


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How do plants get nutrients and water up

xylem?

Transport in plants

Xylem includes 2 types of dead, hollow, tubular cells

Vessel members: slightly large diameter; cellsstacked

Tracheids: smaller diameter; side to side overlap

Vessel members only occur in angiosperms .

T t i l t


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How do plants get nutrients and water up

xylem?

Transport in plants

Water molecules sticks to walls of xylem(adhesion) and to each other (cohesion)

Water moves through xylem in unbroken

column Air on leaf surfaces causes water to

evaporate, creating a pull on the water

column Essentially, osmotic pressure of air isgreater than osmotic pressure withinleaves Process of evaporative water loss inplants

is called trans iration


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Water transport in 3 parts

Transpiration (or evapo-transpiration) isthe transport of water and minerals fromroots to leaves. It involves three basicsteps:

1.Absorption at the roots.

2.Capillary action in the xylem vessels.

3.Evaporation at the leaf.

Mineral and water uptake


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Mineral and water uptakeby Roots4-step process:

-Activetransport ofminerals into roothairs.

-Diffusion tothe pericycle.

-Activetransport into the

vascularcylinder.

-Diffusion intothe xylem.


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Casparian Strip

The Casparian stripcontrols watermovement into the

vascular cylinder ofthe root.Water cannot move

between cells. It

must move throughthe cells by osmosis.


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Microbial helpers

Mycorrhizalfungi help

plants absorbminerals byextending thesurface area of

roots.


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Microbial helpers

Nitrogen-fixingbacteria in rootnodules helpplants acquirenitrogen.

N-fixing bacteriaare associatedmostly withlegumes andalder trees.


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Step 2: Capillary action

Cohesion: polarwater moleculestend to sticktogether withhydrogen bonds.

Adhesion: watermolecules tend tostick to polarsurfaces.


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Capillary action

Cohesion andadhesion causewater to crawlup narrow tubes.

The narrower thetube the higherthe same mass ofwater can climb.

Maximum height:32 feet.


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Cohesion-tension theoryCohesion between water molecules creates

a water chain effect.As molecules are removed from the column

by evaporation in the leaf, more are drawnup.


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Back to the roots...Pressure differences created by transpiration

draws water out of the roots and up thestems.

This creates lower water pressure in theroots, which draws in more water.


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Part 3: Evaporation

Evaporation at the surface of the leaf keepsthe water column moving.This is the strongest force involved in

transpiration.


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Transpiration


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Definition

Transpiration is the evaporation of waterfrom the aerial parts of plants.

Of all the water plant absorbs, over 95-99% is

transpired to the air as water vapor.

F h t i


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From where water istranspired?

Aerial parts of whole young plant Lenticels (lenticular transpiration) 0.1%

-woody stems have loosely packed cork cellsthrough which gas exchange occurs-a little

water is lost here. Cutin (cuticular transpiration) 3%~10%

-the waxy layer,some water is lost throughdiffusion. Stomatum (stomatal transpiration) ~ 90%

-in the leaves, controlled by guard cells.


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Stomatal Transpiration

Stomatum (stomataltranspiration) ~ 90%


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Cuticle

Cuticle

Mesophyll

Stomata Guardcells

Preventswater loss

Site ofphotosynthesis

Openings allowgases and water tomove in and out of

Open and

close thestomata

Stomataltranspiration

I t f


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Importance oftranspiration

Photosynthesis is a process involves usingCO2 and H2O releasing O2 , used to make

CarbohydratesGuard cells prevent excess water lossthrough transpiration.

H2O

CO2

O2


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Factors influencing stomatalaperture

LightTemp.

CO2Water contentPlant hormone


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1. Light

Stomata of most plant open in the day andclose at night, while CAM plants are just theopposite.

Stomata opening are sensitive to red light

and blue light, and blue light is moreeffective, it stimulates opening by a blue-light receptor: zeaxanthin.


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2. Temperature

Stomatal aperture increase with temp. within20- 30 (the optimal).

Low CO2 conc. promotes stomatalopening, while high CO2 conc. inhibits

stomatal opening through itsacidification of the guard cell .

3.CO2


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4. Water contentStomata open when the leaf contains enough

water. When there is a water shortage, theyclose.

5. PlanthormonesCytokinins promotes opening of stomata.

Abscicic acid inhibits opening ofstomata.

Factors that influence


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Factors that influencetranspiration

Transpiration from the leaf depends ontwo major factors:

1. The driving force of transpirationis the Difference in water vaporgradient

2. Diffusional resistance

comprises stomatal resistanceand boundary layer resistance


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vaporpressuregradient.

Diffusional resistance


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Transpiration rate

=Driving force/resistance

water vapor inside the leaf - water vapor of theair

= stomatal resistance + boundary layerresistance

Environmental factors that


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affect the rate oftranspiration

1. Light

Plants transpire more rapidly in the lightthan in the dark. This is largely because

light stimulates the opening of thestomata , Light also speeds up transpirationby warming the leaf .

Contd


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2. Temperature

Plants transpire more rapidly at highertemperatures because water evaporates morerapidly as the temperature rises.

3. HumidityWhen the surrounding air is dry, diffusion ofwater out of the leaf goes on more rapidly.

Contd


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4. WindWhen a breeze is present, the humid airis carried away and replaced by drier air.

5. Soil waterA plant cannot continue to transpirerapidly if its water loss is not made up byreplacement from the soil.

G tt ti


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Guttation

Guttation release of water droplets atleaf tips; occurs when too much water isabsorbed by plant & when humidity is high


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Tropic responses

Directional movements by growth in response

to a directional stimulus


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Phototropism

G th t


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Growth movement


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Phototropisms

Phototropic responses involve bending ofgrowing stems toward light sources. Individual leaves may also display phototrophic

responses.

auxin most likely involved

l d i


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Plants Respond to Gravity

Gravitropism is the response of a plantto the earths gravitational field. present at germinationauxins play primary role

Four stepsgravity perceived by cell

signal formed that perceives gravity

signal transduced intra- and intercellularly

differential cell elongation

G i i


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Gravitropism

Increased auxin concentration on the lowerside in stems causes those cells to growmore than cells on the upper side. stem bends up against the force of gravity

negative gravitropismUpper side of roots oriented horizontally

grow more rapidly than the lower side roots ultimately grow downwardpositive gravitropism

Gravitropism = Geotropism


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Gravitropism = Geotropism

Pl R d T h


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Plants Respond to Touch

Thigmotropism is directional growthresponse to contact with an object. tendrils

Thi t i


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Thigmotropism

SEISMONASTY - a nastic responseresulting


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resultingfrom contact or mechanical shakingMimosa pudica L. (sensitive plant)

NYCTINASTY


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NYCTINASTY

sleepmovements

prayer plant -lower leaves

during the dayand raisesleaves at night

shamrock

(Oxalis

) legumes

Credit:(http://employees.csbsju.edu/ssaupe/biol327/Lab/movie/movies.htm)


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Q N0 1


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Q.N0.1

Plants synthesize auxin from the amino acidA)cystine.B)phenylalanine.C)ornithine.D)tryptophan.E)lysine.

Q N0 2


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Q.N0.2

__________________ is produced in largequantities in the climacteric phase of fruitripening.

A)Auxin

B)Abscisic acidC)Cytokinin

D)Ethylene

E)Gibberellin

Q N0 3


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Q.N0.3

Auxin is synthesized in plants fromA)adenineB)prolineC)aspartaneD)phenylalanine E)tryptophan

Q N0 4


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Q.N0.4

_______________ stimulates the production ofhydrolytic enzymes.

A)EthyleneB)Auxin

C)GibberellinsD)CytokininE)Indoleacetic acid

Q N0 5


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Q.N0.5

Environmental signals influence thedistribution of an auxin in a plant by

A)decreasing the cell's sensitivity to theauxin

B)causing auxin to migrate to the lightedportion

C)destroying the auxin D)causing auxin to migrate into the shaded

portionE)causing the plant to produce more auxin

Q N0 6


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Q.N0.6

________________ , in combination with auxin,stimulates cell division in plants anddetermines the course of differentiation.

A)Ethylene

B)Indoleacetic acidC)GibberellinsD)Abscisic acid E)Cytokinin

Q N0 7


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Q.N0.7

Auxin increases the _______________ of cellwalls.

A)plasticityB)thicknessC)porosityD)layersE)rigidity

Q N0 8


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Q.N0.8

"Foolish seedling" disease in rice is causedby

A)auxins B)gibberellinsC)cytokininsD)ethyleneE)abscisic acid

Q N0 9


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Q.N0.9

In vascular plants, most cytokinins areproduced in the

A)rootsB)shootsC)flowersD)leavesE)lateral branches

Q N0 10


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Q.N0.10

Ripening of fruits, such as bananas, ishastened by

A)gibberellinsB)abiscisic acidC)cytokininD)indoleacetic acid E)ethylene

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Q.N0.11

_______________ of plants are reversible andallow the plant to advantageously orientleaves.

A)Thigmotropisms

B)Turgor movementsC)PhotoropismsD)GravitropismsE)Abscisions

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Q.N0.12

One of the most important uses of auxins isthe _______________ of abscission.

A)initiationB)acceleration

C)stimulation D)preventionE)reinforcing

Q N0 13


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Q.N0.13

Which of the following plant hormones inincorrectly paired with its function?

A)auxins -- responsible for apical dominanceB)abscisic acid -- regulates the rate of

transpirationC)cytokinins -- delays senescence (aging and

decay)D)ethylene -- promotes ripening E)gibberellins -- promotes bud and seed

dormancy

Q N0 14


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Q.N0.14

Lateral stem development is controlled bythe relative levels of

:A)cytokinins and auxinsB)abscisic acid and auxins

C)auxins and gibberellinsD)auxins and ethyleneE)cytokinins and ethylene

Q N0 15


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Q.N0.15

The hormone responsible for phototropicresponses in the growing tips of plants is:

A)auxinB)cytokinin

C)gibberellinD)ethyleneE)abscisic acid

Q N0 16


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Q.N0.16

Tomatoes can be artificially ripened throughthe use of:

A)auxinB)cytokinins

C)gibberellins D)ethyleneE)abscisic acid

Q N0 17


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Q.N0.17

Roots grow downward as a weak_______________ response.

A)negative phototropicB)positive phototropicC)negative gravitropicD)negative thigmotropicE)positive thigmotropic

Q N0 18


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A sunflower plant bends towards thesun. It is ______ response.

A)Thigmonastic

B)seismonasticC)thermonastic

D)photonastic

Q.N0.18

Q N0 19


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The leaves of mimosa are sensitive to______.

A) light

B)touchC) heat

D)smell

Q.N0.19

Q N0 20


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Which of the following showsthigmonastic response ?

A) Sun flower

B) Insectivorous plantsC) Lotus

D) Bryophyllum

Q.N0.20

Q N0 21


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Q.N0.21

Unlike tropisms, nastic movements are inresponse to

A)darknessB)wind

C)non-directional stimuliD)directional stimuli

State TRUE / FALSE


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State TRUE / FALSE

1.A hormone originating in the terminal budof a plant suppresses the growth of lateralbuds.

A)True B)False

2.The response of a plant to touch is calledthigmotropism.

A)True B )False

3.Plant hormones can stimulate certainphysiological processes while inhibiting others.

A)True B)False

Last


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If you were an aquatic plant

where would your stomatabe?

Fringed Water-lily

LastQuestion


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Stomata are foundonly on the upper epidermis

because the lower epidermis is

submerged in water.


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Any Question ????


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Thank YOU !!!!

All THE BEST !!!!

pgb plant hormones gsbtm final

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