32 Lecture Presentation Auto Saved] Lecture

8/4/2019 32 Lecture Presentation Auto Saved] Lecture

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THE UPTAKE AND TRANSPORTOF PLANT NUTRIENTS

Copyright 2009 Pearson Education, Inc.


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32.1 Plants acquire their nutrients from soil andair

Plants take up carbon

dioxide from the air toproduce sugars viaphotosynthesis; oxygen isproduced as a product ofphotosynthesis

Plants obtain water,minerals, and some oxygenfrom the soil

Using simple sugars as an

energy source and asbuilding blocks, plantsconvert the inorganicmolecules they take upinto the organic molecules

of living plant tissueCopyright 2009 Pearson Education, Inc.

CO2

O2

H2O

Minerals


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Inorganicmolecules takenup by plants

Carbon dioxide

Nitrogen

Magnesium

Phosphorus

32.1 Plants acquire their nutrients from soil andair


Organicmoleculesproduced byplants

- Carbohydrates

- Lipids

- Proteins

- Nucleic acids


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Two pathways by whichwater and minerals enterthe xylem

*Intracellular routewater and solutes areselectively taken up bya root epidermal cell,usually a root hair,

and transported fromcell to cell throughplasmodesmata

*Extracellular routewater and solutes pass

into the root in theporous cell walls ofroot cells; they do notenter any cell plasmamembrane until theyreach the root

endodermis

32.2 The plasma membranes of root cells control solute uptake


Extracellular route,via cell walls;stopped by

Casparian strip

Casparian strip

Intracellularroute, via

cell interiors,through

plasmodesmata

Ground tissue system

Dermal tissue system

Vascular tissue system

Key

Root hair

Plasmodesmata

Epidermis Endodermis

Cortex

Xylem

Root hair Epidermis Phloem

Routes of water and solutes from soil to root xylem


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The cells of the endodermis contain a waxy barriercalled the Casparian strip

Specialized cells of the endodermis take up waterand minerals selectively

Regulates uptake of minerals that enter the rootvia the extracellular route

32.2 The plasma membranes of root cells controlsolute uptake


Water uptake requires an osmotic gradient.

Solutes, especially mineral ions, are actively pumpedinto cells by membrane pumps that use ATP.

Selection of minerals that enters the vascular cylinderis controlled by endodermal cells.


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32.3 Transpiration pulls water up xylem vessels

Xylem sap is the solution carried up through a

plant in tracheids and vessel elements

Xylem sap is pulled up through roots and shoots tothe leaves

Transpiration = evaporation of water from thesurface of leaves, and is the driving force for themovement of xylem sap

Waters cohesion and adhesion allow water to bepulled up to the top of the highest trees



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Transpiration-cohesion-tension mechanism

Waters cohesion describes its ability to stick toitself

Waters adhesion describes its ability to stick toother surfaces

A steep diffusion gradient pulls water molecules fromthe surface of leaves into much drier air

The airs pull on water creates a tension that pullson water in the xylem; since water is cohesive, it ispulled along, much as when a person sucks on a straw

32.3 Transpiration pulls water up xylem vessels



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(regulated by guard cellssurrounding stomata)

H2O

H2O

Cohesion and adhesion in xylem

Transpiration

Water uptake

(cohesion of H2O molecules toeach other and adhesion of H2Omolecules to cell walls)

(via root hairs)

THE FLOW OF WATER UP A TREE


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Transpiration

Outside air

Stoma

Air space within leaf

Mesophyll cells

Xylem sap

1

Cohesion andadhesion in the xylem

Xylemcells

Cohesionby hydrogenbonding

2

Root hair

Soil particle

Water

Water uptake from soil

3

Adhesion

Cellwall

4

Water

molecule

THE FLOW OF WATER UP A TREE


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Water loss is lower at night due to high relative humidity of airTranspiration is faster when humidity is low & temp. is high


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32.4 Guard cells control transpiration


Stomata openwhenguard cells take up water Potassium is actively taken upby guard cells from nearby cells This creates anosmotic gradientand water follows

Uneven cell walls of guard cellscauses them to bowwhen water is taken up

The bowing of the guard cellscauses the pore of the stoma to openWhen guard cells lose K+ ions,the guard cells becomeflaccid and the stoma closes

Stoma opening Stoma closing

Stoma Guard cells

Vacuole

H2OH2O

H2O

H2O H2O H2O

H2O

H2OH2O

H2O

K+


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Several factors help regulate guard cell activity

In general, stomata are open during the day andclosed at night

Sunlight signals guard cells to accumulate K+ andopen stomata

Low CO2 concentration in leaves also signals guardcells to open stomata

Plants have natural rhythms that help them close

stomata at night to conserve water Plants may also close stomata during the day to

conserve water when necessary

32.4 Guard cells control transpiration



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32.5 Transport of Organic Substances in Phloem

Phloem transports theproducts of photosynthesis

throughout the plant Phloem sap moves

through sieve plates insieve tube members

Phloem sap is

composed ofsucroseand other solutessuch as ions, aminoacids, and hormones

Sugars are carried

through phloem fromsources to sinks


Sieveplate

Sieve-tubemember

A Food-conducting cells of phloem


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Asugar source is aplant organ that is a

net producer of sugarvia photosynthesis(leaves)

Asugar sinkis a plantorgan that is a netconsumer of sugar orone that storesstarch

Growing organs usesugar in cellularrespiration

Roots and otherorgans store unusedsugars as starch



Sugarsink

High sugarconcentration

Sugar

Water

Sugar

Water

XylemPhloem

Sieve plate

Sourcecell

High water pressure

Low water pressure

Low sugar

concentration

1

2

3

4

Sinkcell

Sugarsource


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The pressure flow mechanism

At sources, sugars are

actively loaded into sievetube members

High solute concentrationcaused by the sugar in sievetubes causes water to rushin from nearby xylem cells

Flow of water into sievetubes increases pressure atsources

At sinks, sugars areunloaded from sieve tubesand solute concentration

decreases; water is lostand pressure is low

The pressure gradient drivesrapid movement of sugarsfrom sources to sinks



"source-to sink" patternSource: leavesSinks: fruits, seeds, roots

Translocation through the phloem depends on pressure gradients

between source and sink regions.


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PLANT NUTRIENTSAND THE SOIL



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Macronutrientscomponents of organic molecules(Plants require relatively large amounts)

Carbon

Hydrogen

Oxygen

Nitrogen

Sulfur

Phosphorus Potassium

Calcium 1.5 %

Magnesium

Make up 98% ofplant dry weight

Major ingredients of organic compoundsforming the structure of a plant

32.6 Plant health depends on a complete diet ofessential inorganic nutrients



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Micronutrientsoften act as cofactors(Plants need in very small amounts)

Chlorine

Iron Manganese

Boron

Zinc

Copper

Nickel

Molybdenum

32.6 Plant health depends on a complete diet ofessential inorganic nutrients



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Solution lacking

potassium (experimental)

Complete solution containing

all minerals (control)

A hydroponic culture experiment(used to determine which chemical elements are essential nutrients)


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32.7 CONNECTION: Fertilizers can help preventnutrient deficiencies

The availability of nutrients in soil affects plantgrowth and health

Growers can often determine which nutrients are

missing from soil by looking at plant symptoms Nutrient deficiencies can be alleviated by adding

inorganic chemical fertilizers or compost tosoil

Nitrogen is the element that most commonlylimits plant growth in nature



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The effect of nitrogen availability on corn growth: corn grown

in nitrogen-rich soil (left) and nitrogen-poor soil (right)

Wh i i i li i d l h hibi f h d fi i


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When macronutrients or micronutrients are limited to plants, they exhibit symptoms of the deficiency.


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32.8 Fertile soil supports plant growth

Soils are affected bygeography and climate

Soil horizons are layers ofsoil with differentcharacteristics

A horizontopsoilsubject to weathering; layercontains humus (decayedorganic matter) and manysoil organisms

B horizonclay anddissolved elements

C horizonrocks of theparent material fromwhich soil is formed


B

A

C

Three soil horizons visible beneath grass


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Asoils physical andchemical characteristics

affect plant growth

Soil particle sizesinfluence theamount of waterand air present in a

soil

Soil particles andplant rootsparticipate in cationexchangethe

transfer of positiveions such ascalcium,magnesium, andpotassium from soil

to plant roots

32.8 Fertile soil supports plant growth


Clayparticle

Root hair

K+

K+

K+

K+K

+

K+K+

K+

H+

Cation exchange


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32.9 CONNECTION: Soil conservation is essentialto human life

Human practices inagriculture havedegraded soils

Irrigation can causebuild up ofsalts insoils

Plowed lands aresubject to erosion bywind and rain, which

removes topsoil

Chemical fertilizersare costly and maycontaminategroundwater


Soil conservationefforts are needed toreduce the problemsassociated withagriculture

Efficient dripirrigation

Practices toreduce erosion

Alternatives totraditionalfertilization


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Flood irrigation Planting to prevent soil erosion in a hilly area

Modern irrigation=employs perforated pipesthat drip water slowly into the soil close toplant roots.

Crops are planted in rows that go around.This helps slow the runoff of water & topsoilAfter heavy rains.


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PLANT NUTRITIONAND SYMBIOSIS



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32.12 Most plants depend on bacteria to supplynitrogen

Most of the nitrogenin the biosphere is in theatmosphere as N2 gas

Plants can only absorb nitrogen as ammonium ornitrates from the soil; they cannot absorb it from air

Soil bacteria can convert N2 gas from the air intoforms usable by plants via several processes

Nitrogen fixationN2 is converted to ammonia

Amonificationconversion oforganic matter into ammonium

Nitrificationconversion ofammonium to nitrates, the formmost often taken up by plants


Atmosphere


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Atmosphere

Soil

Nitrogen-fixingbacteria

N2

N2

H+

NH3

NH4+

(ammonium)NO3

(nitrate)

NH4+

Aminoacids, etc.

NitrifyingbacteriaAmmonifying

bacteriaOrganicmaterial Root

The roles of bacteria in supplying

nitrogen to plants

32 13 EVOLUTION CONNECTION M ll


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32.13 EVOLUTION CONNECTION: Mutuallybeneficial relationships have evolvedbetween plants and their symbionts

Most plants form symbioses with fungi called mycorrhizae

Mycorrhizae act like extensions of plant roots, increasing the area forabsorption of water and minerals from soil

Mycorrhizae produce enzymes that release phosphorus from soil, making it

available to plant hosts Mycorrhizae release growth factors and antibiotics into the soil

Mycorrhizal symbioses have evolved with plants and were important toplants successfully invading land


A mycorrhiza on a eucalyptus root

A mycorrhiza is an association between a fungus and

a vascular plant which increases the absorptivesurface area of the plant.

The plant gets water and dissolved nutrients;the fungus gets carbohydrates produced by the plant.

32 13 EVOLUTION CONNECTION M ll


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Some plants form symbioses with nitrogen-fixing bacteria (contain enzyme nitrogenase)

Legumes (peas, beans, alfalfa, and others) form rootnodules to house nitrogen-fixing symbionts in the genus

Rhizobium

Plants that form these associations are rich innitrogen

Both mycorrhizae and nitrogen-fixing bacteriabenefit by receiving sugars from the plants theycolonize

32.13 EVOLUTION CONNECTION: Mutuallybeneficial relationships have evolvedbetween plants and their symbionts



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Roots

Shoot

Nodules

Root nodules on a pea plant


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Bacteria

within vesicle

Bacteria within a root nodule cell

32 14 Th l t ki d i l d i h t


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32.14 The plant kingdom includes epiphytes,parasites, and carnivores

Epiphytes Grow anchored on other plants

Absorb water and minerals from rain

Parasites

Roots tap into the host plants vascular system

Incapable of photosynthesis

Absorb organic molecules from host plant

Carnivores Trap and digest small animals such as insects

Absorb inorganic elements from prey

Found in nutrient poor environments



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Dodder

Orchid

Venus flytrap Mistletoe

Sundew plant


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PHYTOREMEDIATION: Use of plants to remediate polluted soil and/or groundwater


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(regulated by guard cellssurrounding stomata)

H2O

H2O

Cohesion and adhesion in xylem

Transpiration

Water uptake

(cohesion of H2O molecules toeach other and adhesion of H2Omolecules to cell walls)

(via root hairs)


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(a) (b) (c)

(e) (f)

(d)

from through

driven bydriven by to

sugar

throughfrom

to

Transportin plants

involves movement of

water andminerals

leavespressure

flow


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Water loss is lower at night due to high relative humidity of air

Y h ld b bl t


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You should now be able to

1. Describe phytoremediation and its uses2. Explain how water and minerals are taken up by

plant roots

3. Describe the transpiration-cohesion-tensionmechanism for movement of water through plants

4. Describe how guard cells regulate transpiration

5. Explain how sugars are transported through plantsfrom sources to sinks




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6. Give examples of essential elements and tell whythey are important

7. Explain how soil characteristics and fertility

influence plant growth8. Give examples of ways that agriculture can

degrade soil and practices that help conserve soil

9. Describe organic agriculture and its aims





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10. Give examples of ways genetic engineering hasbeen used to preserve the environment andimprove crops

11. Explain why soil bacteria are important to all

plants and plant nutrition

12. Describe the symbiotic relationships that haveevolved between plants and microorganisms and

how those relationships improve plant nutrition13. Differentiate between epiphytes, parasites, and

carnivorous plants; describe what each of thesekinds of plants gets from its host or prey


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