bio 100 chapter 22

Chapter 22Transport and

Nutrition in PlantsLecture Outline

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Plants Are Organized to Transport Water

and Solutes

22-2

22.1 Transport begins in both the leaves and the roots of plants

Xylem Carries water and minerals from the roots to

the leaves In addition to other cell types, 2 types of

nonliving conductive cells Tracheids – tapered at both ends, ends overlap,

and pits allow water to pass between tracheids Vessel elements – long and tubular with

perforation plates at each end, form a completely hollow pipeline from roots to leaves

22-3

22.1 Transport begins in both the leaves and the roots of plants

Phloem Transports sugar to all parts of the plant Composed of several cell types

Sieve-tube members – living conducting cells, contain cytoplasm but have no nucleus

Companion cells – provide proteins to sieve-tube members

Water is a large part of xylem sap and phloem sap

22-4

Figure 22.1 A plant΄s transport system

(blue = phloem; pink =sugar; red = xylem;

light blue = water)

22-5


O2

xylemphloemstoma

CO2

Phloem is transporting sugarfrom the leaf to the root.

H2O

watersugar

H2Osugar

Figure 22.1 A plant΄s transport system

(blue = phloem; pink =sugar; red = xylem;

light blue = water)

22-6


H2Osugar

Xylem transports water andminerals from the root to the leaf.

H2O

Rootphloemxylem

HOW SCIENCE PROGRESSES

22A Competition for resources is one aspect of biodiversity

Minnesota grasslands often harbor more than 100 plant species within only a few hectares

Competing for soil nitrogen and ability to disperse

Mathematical model showed that stable coexistence of a whole range of plant species that differ according to their abilities to compete for nitrogen and to disperse to new areas

Found high biodiversity buffers ecosystems against a distrubance

22-7

Figure 22A.1 Little bluestem Figure 22A.2 Bent grass

22-8


Poor disperser

Good competitorfor nitrogen


Good disperser

Poor competitorfor nitrogen

Figure 22A.3 Results of a study linking water availability to biodiversity

22-9


Pro

po

rtio

n o

f P

re-D

rou

gh

t B

iom

ass 1

0 5 25

Plant Species Richness During Drought

201510

1/16

1/8

1/4

1/2

Xylem Transport Depends on the Properties of Water

22-10

22.2 Water is pulled up in xylem by evaporation from leaves

How is it possible for water to rise to the top of a plant? Root pressure

Water entering root cells creates a positive (internal) pressure compared to the water in the surrounding soil

May contribute to upward movement, but not the primary mechanism

Guttation – drops of water are forced out of vein endings along the edges of leaves

22-11

Figure 22.2A Conducting cells of xylem

22-12


Vessel Element

Single, large opening

20 µm

Vessel Element

Series of openings

20 µm

pits

(both): Courtesy Wilfred A. Cote, from H.A. Core, W.A. Cote, and A.C. Day, “Wood: Structure and Identification” 2/e

Figure 22.2A Conducting cells of xylem (Cont.)

22-13


Tracheids

pits

50 µmCourtesy Wilfred A. Cote, from H.A. Core, W.A. Cote, and A.C. Day, “Wood: Structure and Identification” 2/e

Figure 22.2B Guttation

22-14


Cohesion-Tension Model Requires no expenditure of energy by the plant and is

dependent on the properties of water Cohesion – tendency of water molecules to cling

together Water molecules form a continuous water column

in xylem, from the leaves to the roots Adhesion – ability of water to interact with the

molecules making up the walls of the vessels in xylem Gives the water column extra strength and

prevents it from slipping back22-15


What happens in the leaf? Evaporation of water through leaf stomata is called

transpiration At least 90% of the water taken up by the roots is

eventually lost by transpiration Transpiration exerts a pulling force, or tension, that draws

the water column through the xylem to replace the water lost by leaf cells

What happens in the root? Due to the active transport of minerals into the root water

enters root hairs passively by osmosis, and from there it enters xylem

22-16

Figure 22.2C Cohesion-tension model of xylem transport

22-17


1

xylem

mesophyllcells

Leaves•Transpiration creates tension.•Tension pulls the water column upward from the roots to the leaves.

H2O

intercellularspace

stoma

cohesion due to hydrogen bondingbetween water molecules

adhesion due topolarity ofwater molecules

cell wall

water molecule

(tree): © Paul Davies/Alamy

Figure 22.2C Cohesion-tension model of xylem transport

22-18


2

3

xylem

xylem

root hair

Roots•Water enters xylemat root.•Water columnextends fromleaves

Stem•Cohesion makeswater columncontinuous.•Adhesion keepswater column inplace.

(tree): © Paul Davies/Alamy

22.3 Guard cells regulate water loss at leaves

Stoma (pl., stomata) – small pore in leaf epidermis bordered by modified epidermal cells called guard cells Water enters the guard cells stoma opens Water exits the guard cells stoma closes

Entrance of K+ into guard cells creates osmotic pressure causing water to follow and stoma opens Stoma closes when turgor pressure decreases due to

the exit of K+ followed by the exit of water

22-19

Figure 22.3A A stoma opens when turgor pressure increases in guard cells due to the entrance of K+ followed by the entrance of water

22-20


K+

25 µmK+ enters guard cells and water follows.

H2OH2O

vacuole

guard cell

stoma

(Right): © Jeremy Burgess/SPL/Photo Researchers, Inc.

Figure 22.3B A stoma closes when turgor pressure decreases due to the exit of K+ followed by the exit of water

22-21


(Right): © Jeremy Burgess/SPL/Photo Researchers, Inc

K+

H2OH2O

25 µmK+ enters guard cells and water follows.

22.3 Guard cells regulate water loss at leaves

3 other factors aside from water availability regulate whether stomata open or close1. Presence of light causes stomata to open

2. High concentration of CO2 causes stomata to close

3. Abscisic acid (ABA) by cells in wilting leaves causes stoma to close

22-22

HOW BIOLOGY IMPACTS OUR LIVES

22B Plants Can Clean Up Toxic Messes

Phytoremediation Use of plants to clean up pollutants

2 basic ways plants clean up sites1.Organics broken down by plants or microbes, remainder

absorbed by plant or left in soil

2. Inorganics absorbed and trapped inside plant, plant then harvested to be disposed of or reclaimed

Limitations of phytoremediation Slow pace, shallow depth (roots) Will not work on lead and other metals unless other

chemicals are added to the soil22-23

Figure 22B Scientist Gary Bañuelos in a field of canola plants

22-24

Canola plants are grown in California’s

San Joaquin Valley to soak

up excess selenium in

the soil

Phloem Function Depends on Membrane Transport

22-25

22.4 Pressure flow explains phloem transport

Plants transport the organic molecules resulting from photosynthesis to the parts of plants that need them

Aphids and radioactive 14C tracers are used to follow sugar from source to sink Aphids are phloem feeders and are used to extract

sap from phloem Sap movement through phloem can be as fast as 60–

100 cm per hour and possibly up to 300 cm per hour

22-26

Figure 22.4A Aphid acquiring phloem sap

22-27


Under microscope

An aphid feeding on a plant stem

waste due to feedingon phloem sap

(top): © Bruce Iverson/SPL/Photo Researchers, Inc.; (bottom):From M.H. Zimmerman "Movement of Organic Substances in Trees" in SCIENCE 133 (13) January 1961

22.4 Pressure flow explains phloem transport

Pressure-flow model Explanation for the movement of organic

materials throughout the plant in phloem Flow Is from a Source to a Sink

During the growing season, leaves photosynthesize and are a source of sugar

Roots, which are growing, are a sink for sugar

Transport of Sugar Transport can account for any direction of flow in sieve

tubes if we consider that the direction of flow is always from source to sink

22-28

Figure 22.4B Bulk flow due to a pressure gradient

22-29


H2O

H2O H2O

Bulb2:dilutesucrosesolution

Bulb1:concentratedsucrosesolution

differentially permeable membranes

pressure flow of solution

31

2

Figure 22.4C The pressure-flow model of phloem transport says that sugar is transported in phloem from a source (e.g.,photosynthesizing leaves) to a sink (e.g., actively metabolizing roots)

22-30


1

palisade mesophyllcell of leaf

xylem phloem

Leaf

sugarwater

7

2

xylemphloem

6 3

4

5cortex cellof root

xylemphloem Root

watersugar

Plants Require Good Nutrition and Therefore Good Soil

22-31

22.5 Certain nutrients are essential to plants

Approximately 95% of a typical plant’s dry weight is carbon, hydrogen, and oxygen

Minerals as Nutrients Mineral – inorganic substance usually containing two

or more elements needed to help build molecules Essential nutrients

Has an identifiable role No other nutrient can substitute and fulfill the same roll A deficiency of this nutrient causes a plant to die or fail to

complete its reproductive cycle

22-32

22.5 Certain nutrients are essential to plants

Minerals as Nutrients Essential nutrients divided into

Macronutrients – needed in large quantity Micronutrients – needed in trace amounts

Beneficial nutrients either are required for or enhance the growth of a particular plant

Hydroponics allows plants to grow in water, instead of soil, if they are supplied with all the nutrients they need

22-33

22-34

Figure 22.5A Overview of plant nutrition


H20

O2

CO2

CO2

O2

H2O

Water evaporatesfrom leaves.

Oxygen escapes fromphotosynthesizing leaves.

Carbondioxideenters photo-synthesizingleaves.

Water entersroots.

Minerals enterroots.

mineralsOxygen enters andcarbondioxide exitsrespiring roots.

C

C

H O P K N S B

MicroMacro

Hopkins Cafe Managed By Mine Cousin Clyde Mo

MoClZnMn CuMgFeCa

Figure 22.5B Effects of nutrient deficiencies

22-37



solution lacks nitrogen complete nutrition solution

solution lacks phosphorus complete nutrition solution(both): Courtesy Mary E. Doohan

Figure 22.5B Effects of nutrient deficiencies (cont.)

22-38


Courtesy Mary E. Doohan

solution lacks calcium complete nutrition solution

22.6 Roots are specialized for the uptake of water and minerals

Soil is a mixture of mineral particles (sand, silt, and clay), decaying organic material, living organisms, air, and water, which together support the growth of plants

Soil that contains a high percentage of decomposing organic material is called humus

A soil profile is a vertical section of soil, from the ground surface to the unaltered rock below.

Usually, a soil profile has parallel layers known as horizons

22-39

22-40

Figure 22.6A Simplified soil profile and minerals in soil


So

il ho

rizon

s

A

B

C

root hair

negatively charged soil particle cortex

epidermis of root

film of water

b. Minerals in soil

air space

a.Simplified soil profile

Topsoil :humusplus livingorganisms

Zone of leaching:removal of nutrients

Subsoil:accumulationof minerals andorganic materials

Parent material:weathered rock

Ca2+

Ca2+

Ca2+

Ca2+

Ca2+

K+

K+ K+

K+

K+

K+

22.6 Roots are specialized for the uptake of water and minerals

In order for water to reach the xylem of a root, it must pass through the cortex in one of two ways Apoplast route – between cells Symplast route – through cells using plasmodesmata

Regardless of pathway, water enters root cells by aquaporins

Minerals are actively taken up by plant cells Astonishing ability to concentrate minerals Ions need to be actively transported into plant cells

22-41

Figure 22.6B Apoplast and symplast routes

22-42


50 µm

a.

symplast routeof water and

mineralsroot hair

epidermisapoplast routeof water and

minerals

cortex

endodermisandCasparianstrip

pericycle

vascular cylinder

endodermis

pericycle

phloem

xylem

cortex

(Top left): © CABISCO/Phototake

22-43

Figure 22.6B Apoplast and symplast route of uptake (cont.)Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

1 2

3

P+

K+

K+

K+

K+

K+

K+

H+

ATP

H+

H+

An ATP-drivenpump transportsH+ outofcell.

The electrochemicalgradient causes K+

to enter by way of achannel protein.

Endodermal Cell

b.

Water Outside Endodermal Cell

H+

H+

I–

I–I–

I–

I–

ADP

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

I–H+

22.7 Adaptations of plants help them acquire nutrients

Root Nodules Some plants, such as legumes, soybeans, and alfalfa,

have roots colonized by Rhizobium bacteria Rhizobium can reduce atmospheric nitrogen (N2) to

NH4+ for incorporation into organic compounds

Mycorrhizae Involves fungi and almost any type of plant root Fungus increases the surface area available for

mineral and water uptake and breaks down organic matter in soil

22-44

Figure 22.7A Root nodules

22-45


noduleroot

bacteria

Portion of infected cell(root nodules): © Dwight Kuhn; (cell): © E.H. Newcomb & S.R. Tardon/Biological Photo Service

Figure 22.7B Mycorrhizae result in better growth

22-46


Mycorrhizae present

Mycorrhizae not present

mycorrhizae

(plants, top): © Runk/Schoenberger/Grant Heilman Photography; (mycorrhizae, circle): © Dana Richter/Visuals Unlimited

Figure 22.7C Dodder twists around host

Parasitic plants, such as dodders, broomrapes, and pinedrops, send out rootlike projections called haustoria that tap into the xylem and phloem of the host stem

22-47© Kevin Schafer/Corbis


dodder(brown)

Figure 22.7D Sundews are carnivorous

Carnivorous plants, such as the Venus flytrap and the sundew, digest insects as a source of nitrogen

By-pass need for nitrates from soil which may be lacking

22-48


bulbs releasedigestive enzymes

stickyhairs

narrowleafform

Sundew leafenfolds prey

(sundew leaf, prey): © Dr. Jeremy Burgess/Photo Researchers, Inc .

Connecting the Concepts:Chapter 22

The evolution of a transport system was critical, however, in order for plants to make full use of advantages of land environment

Presence of a transport system allows materials to be distributed to those parts of the plant body that are growing most rapidly

Another benefit of a transport system is distribution of hormones that regulate plant responses to the environment

22-49

bio 100 chapter 22

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