Bio 100 Chapter 22

Chapter 22
Transport and
Nutrition in Plants
Lecture Outline
See PowerPoint Image Slides
for all figures and tables pre-inserted into
PowerPoint without notes.

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

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
water (blue = phloem;
sugar pink =sugar;
xylem red = xylem;
phloem light blue = water)
stoma
O2 CO
2

H2O Phloem is transporting sugar
from the leaf to the root.
sugar
H2O

22-5


Figure 22.1
A plant΄s transport system
(blue = phloem;
pink =sugar;
red = xylem;
light blue = water)

Xylem transports water and
minerals from the root to the leaf.
sugar
H2O

H2O

xylem
phloem Root 22-6

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

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

Good disperser
Poor disperser

Good competitor
for nitrogen Poor competitor
for nitrogen

Figure 22A.1 Little bluestem Figure 22A.2 Bent grass
22-8

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


1
Proportion of Pre-Drought Biomass

1/2

1/4

1/8

1/16

0 5 10 15 20 25
Plant Species Richness During Drought

22-9

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


Vessel Element Vessel Element

Single, large opening Series of openings

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

pits

22-12

Figure 22.2A Conducting cells of xylem (Cont.)

Tracheids

pits

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

22-13

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 back
22-15

 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
mesophyll
xylem cells

1 Leaves
stoma
•Transpiration creates
tension. intercellular
•Tension pulls the water space
column upward from the H2 O
roots to the leaves.

cohesion due to hydrogen bonding
between water molecules

adhesion due to
polarity of
water molecules

cell wall

water molecule

(tree): © Paul Davies/Alamy

22-17

Figure 22.2C
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cohesion-tension
model of xylem
transport
2 Stem
•Cohesion makes
water column
continuous.
•Adhesion keeps
water column in
place. xylem

root hair

3 Roots
•Water enters xylem
at root.
•Water column
extends from
leaves xylem

(tree): © Paul Davies/Alamy

22-18

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


H2O H2O

vacuole K+

guard cell

stoma

K+ enters guard cells and water follows.
25 µm
(Right): © Jeremy Burgess/SPL/Photo Researchers, Inc.

22-20

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


H2O H2O

K+

K+ enters guard cells and water follows. 25 µm
(Right): © Jeremy Burgess/SPL/Photo Researchers, Inc

22-21

22.3 Guard cells regulate
water loss at leaves
 3 other factors aside from water
availability regulate whether stomata open
or close
1. 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 sites
1. 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 soil 22-23

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

Canola plants
are grown in
California’s
San Joaquin
Valley to soak
up excess
selenium in
the soil

22-24

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

Under microscope

waste due to feeding
on phloem sap

An aphid feeding on a plant stem 22-27
(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

pressure flow of solution 2

Bulb1: H2O Bulb2:
concentrated dilute
sucrose sucrose
solution solution

1 H2O H2O 3

differentially permeable membranes 22-29


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

1
2
sugar
water

xylem phloem

6 3

4

cortex cell
5 of root

22-30
xylem
phloem Root

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

Figure 22.5A
Overview of
plant nutrition

Water evaporates
from leaves.

H2 O

CO2 Macro Micro
Carbondioxide
O2 enters photo-
synthesizing Cu Zn Cl Mo
C HOP KNS Ca Fe Mg B Mn
leaves.

Oxygen escapes from
C Hopkins Cafe Managed By Mine Cousin Clyde Mo
photosynthesizing leaves.

Water enters
roots.
H2 0
CO2
O2 Minerals enter
roots.

Oxygen enters and minerals
carbondioxide exits
respiring roots.

22-34

Figure 22.5B
Effects of
nutrient
deficiencies

solution lacks nitrogen complete nutrition solution

solution lacks phosphorus complete nutrition solution 22-37
(both): Courtesy Mary E. Doohan

Figure 22.5B Effects
of nutrient deficiencies
(cont.)

solution lacks calcium complete nutrition solution
Courtesy Mary E. Doohan

22-38

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


negatively charged soil particle cortex

K+

Soil horizons
Topsoil :humus K+ K+
A Ca2+
plus living
organisms root hair Ca2+

Zone of leaching: K+
Ca2+
removal of nutrients

Subsoil: B K+
accumulation Ca2+
of minerals and
organic materials Ca2+ K+
film of water
Parent material:
weathered rock C epidermis of root
air space

a.Simplified soil profile b. Minerals in soil

Figure 22.6A Simplified soil profile and minerals in soil

22-40

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

endodermis

pericycle

phloem
xylem
cortex

50
µm

vascular cylinder

pericycle

endodermis
andCasparian
strip

cortex

epidermis
apoplast route
of water and symplast route
minerals of water and
a. root hair minerals

(Top left): © CABISCO/Phototake
22-42

Figure 22.6B Apoplast and symplast route of uptake (cont.)

1 An ATP-driven 2 The electrochemical Endodermal Cell
pump transports gradient causes K+
H+ outofcell. to enter by way of a H+ I– I–
channel protein.

K+ H+
K +
I– I–
ATP H+ ADP + P
K+
H+
K + I–
K +

H+ I–
K+
H+ H+
H+ 3 Negatively charged ions
(I–) are transported
Water Outside Endodermal Cell along with H+ into cell

b. 22-43

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

root nodule

bacteria

Portion of infected cell
(root nodules): © Dwight Kuhn; (cell): © E.H. Newcomb & S.R. Tardon/Biological Photo Service
22-45

Figure 22.7B Mycorrhizae result in better growth


Mycorrhizae present

Mycorrhizae not present

mycorrhizae

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

22-46


Figure 22.7C Dodder twists
around host

 Parasitic plants,
such as dodders,
broomrapes, and
pinedrops, send
out rootlike
dodder projections called
(brown) haustoria that tap
into the xylem and
phloem of the
host stem
© Kevin Schafer/Corbis

22-47


bulbs release
digestive enzymes Figure 22.7D
Sundews are carnivorous

 Carnivorous
plants, such
as the Venus
Sundew leaf flytrap and
enfolds prey
the sundew,
sticky digest insects
hairs
narrow
as a source
leafform of nitrogen
 By-pass need
for nitrates
from soil
which may be
lacking
(sundew leaf, prey): © Dr. Jeremy Burgess/Photo Researchers, Inc .
22-48

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

More Related Content

Similar to Bio 100 Chapter 22

More from wmk423

Bio 100 Chapter 22