Transcript chapter26_Sections 1-4.ppt

Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 26
Plant Nutrition and Transport
(Sections 26.1 - 26.4)
Albia Dugger • Miami Dade College
26.1 Mean Green Cleaning Machines
• Chemical weapons and explosives, together with plastics,
solvents, and other wastes were burned in open pits at JField, Aberdeen Proving Ground, Maryland
• Lead, arsenic, mercury, and highly toxic organic compounds
such as TCE contaminated the soil and groundwater
• The Army and Environmental Protection Agency turned to
phytoremediation: the use of plants to take up and
concentrate or degrade environmental contaminants
J-Field Weapons Testing
• TCE damages the nervous system, lungs, and liver, and
exposure to large amounts can be fatal
26.2 Plant Nutrients and Soil
• Plant growth requires the sixteen elements:
• Nine elements are macronutrients, required in amounts
above 0.5% of the plant’s dry weight
• Seven other elements are micronutrients, which make up
traces of the plant body
• Carbon, oxygen, and hydrogen are obtained from air and
water
• Other nutrients are taken up by roots as minerals
dissolved in soil water
Plant Macronutrients
Plant Micronutrients
Properties of Soil
• Soil consists of particles from weathered rocks, mixed with
variable amounts of decomposing organic material (humus)
• Mineral particles (sand, silt, and clay) differ in size and
chemical properties
• Sand and silt provide air spaces
• Negatively-charged clay attracts positive mineral ions
• Loams have the best oxygen and water penetration
Key Terms
• soil
• Mixture of various mineral particles and humus
• humus
• Decaying organic matter in soil; provides nutrients;
negatively charged organic acids trap positive mineral ions
• loam
• Soil with roughly equal amounts of sand, silt, and clay
How Soils Develop
• Most soils form in
layers, or horizons, that
are distinct in color and
other properties
• Example: A soil horizon
from Africa
How
Soils
Develop
O Horizon
Fallen leaves and other
organic material littering
the surface of mineral soil
A Horizon
Topsoil, with decomposed organic
material; variably deep [only a few
centimeters in deserts, elsewhere
extending as far as 30 centimeters
(1 foot) below the soil surface]
B Horizon
Compared with A horizon, larger soil
particles, not much organic material,
more minerals; extends 30 to 60
centimeters (1 to 2 feet) below soil
surface
C Horizon
No organic material, but partially
weathered fragments and grains
of rock from which soil forms;
extends to underlying bedrock
Bedrock
Fig. 26.2, p. 416
How Soils Develop
• Topsoil typically contains the greatest amount of organic
matter, so the roots of most plants grow most densely in it
• Leaching carries away soil nutrients; it is fastest in sandy
soils, which do not bind nutrients as well as clay soils
• Nutrients are also lost through soil erosion; strong winds,
fast-moving water, sparse vegetation, and poor farming
practices cause the greatest losses
Key Terms
• Topsoil
• Uppermost soil layer
• Contains the most nutrients for plant growth
• leaching
• Process by which water moving through soil removes
nutrients from it
• soil erosion
• Loss of soil under the force of wind and water
Soil Erosion in Georgia
• A result of poor farming
practices
• Affects not only plants,
but also the organisms
that depend on the
plants for survival
Key Concepts
• Plant Nutrients and Soil
• Many plant structures are adaptations to limited amounts
of water and essential minerals
• The amount of water and minerals available for plants
depends on the composition of soil, which is vulnerable to
leaching and erosion
26.3 How Do Roots Absorb Water and Minerals?
• Root growth is greatest in areas where water and nutrient
concentrations best match the plant’s requirements
• Root specializations such as hairs, mycorrhizae, and nodules
help plants absorb water and nutrients
Root Hairs
• Root hairs (thin
extensions of root
epidermal cells)
enormously increase
surface area absorbing
water and nutrients
• They do not develop
into new roots, and last
only a few days
Root Hairs
root hair
A The hairs on this root of a
white clover plant are about
0.2 mm long.
Fig. 26.4a, p. 418
Mycorrhizae
• Fungal hyphae in and
around roots help roots
absorb mineral ions
from a larger volume of
soil than roots alone
• mycorrhiza
• Mutually beneficial
fungus-plant root
partnership
Mycorrhizae
mycorrhiza
root
B Mycorrhizae (white hairs) extending
from the tip of these roots (tan)
greatly enhance their surface area.
Fig. 26.4b, p. 418
Root Nodules
• Anaerobic bacteria in
root nodules share their
fixed nitrogen with
certain plants
• root nodules
• Swellings of some plant
roots that contain
nitrogen-fixing bacteria
Root
Nodules
root nodule
C Anaerobic bacteria in root nodules on
this soybean plant fix nitrogen from the
air. The nitrogen is shared with the plant.
Fig. 26.4c, p. 418
Nitrogen Fixation
• Nitrogen-fixing bacteria form root nodules on clover, peas,
and other legumes
• In nitrogen fixation, a bacterial enzyme uses ATP to convert
nitrogen gas to ammonia (NH3)
• Other bacteria convert ammonia to nitrate (NO3-), a form of
nitrogen that plants can absorb
• nitrogen fixation
• Conversion of nitrogen gas to ammonia
Control Over Uptake
• Water enters plant cells by diffusing across the plasma
membrane of a cell in the root’s epidermis or cortex
• Mineral ions only enter cytoplasm through active transporters
in the plasma membranes
• Once in cytoplasm, water and ions diffuse cell to cell through
plasmodesmata until they enter xylem in the vascular cylinder
Control Over Uptake (cont.)
• Soil water can only enter the vascular cylinder by passing
through an endodermal cell, which is covered by a waterproof
Casparian strip
• Transport proteins in the cells’ plasma membranes control the
movement of mineral ions from soil water into the plant body
• Casparian strip
• Waxy, waterproof band that seals abutting cell walls of
root endodermal cells
Control Over Uptake
Control Over Uptake
Fig. 26.5a, p. 419
Control Over Uptake
vascular cylinder
epidermis
endodermis
primary phloem
primary xylem
cortex
vascular cylinder
Fig. 26.5a, p. 419
Control Over Uptake
Fig. 26.5b, p. 419
Control Over Uptake
tracheids
and vessels
in xylem
B Parenchyma cells that make
up the layer secrete a waxy
substance into their walls
wherever they touch. The
secretions form a Casparian
strip. A Casparian strip
prevents water from diffusing
through endodermal cell walls
to enter the vascular cylinder.
sieve tubes
in phloem
endodermal cell
Casparian strip
Fig. 26.5b, p. 419
Control Over Uptake
Fig. 26.5c, p. 419
Control Over Uptake
C Soil water can only enter the vascular
cylinder by moving through the cytoplasm
of endodermal cells. Water and ions enter
the cells via plasmodesmata or via
transport proteins in the cells’ plasma
membranes.
Water and ions must cross at least one
cell’s plasma membrane before entering
a vascular cylinder. Thus, plasma
membrane transport proteins control
the movement of these substances
into the rest of the plant.
Vascular
cylinder
Casparian
strip
water and nutrients
Cortex
Fig. 26.5c, p. 419
ANIMATION: Root Functioning
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ANIMATION: Uptake of Nutrients by Plants
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26.4 Water Movement Inside Plants
• Evaporation from leaves and stems drives the upward
movement of water through xylem inside a vascular plant
• Water’s cohesion allows it to be pulled from roots into all other
parts of the plant
The Cohesion–Tension Theory
• Water is pulled upward from roots through continuous
pipelines of xylem by the negative pressure (tension) of
evaporation (transpiration), and cohesion among water
molecules
• cohesion-tension theory
• How transpiration creates a tension that pulls a cohesive
column of water through xylem, from roots to shoots
• transpiration
• Evaporation of water from plant parts
Xylem: Tracheids
and Vessel Members
Xylem: Tracheids
and Vessel Members
vessel member
perforation
plate
perforation
in the side
wall of
tracheid
A The end walls
of tracheids
are tapered and
unperforated.
Perforations in
the side walls of
adjoining tracheids
match up.
B The thick, finely perforated end
walls of dead vessel member cells
connect to make long conducting
tubes of xylem. The micrograph
shows three adjoining vessel
members.
C Vessel members vary in shape. A
perforation plate imparts strength to
a junction where vessel members
meet, while also allowing water to
flow freely in through the xylem tube.
Fig. 26.6, p. 420
Xylem:
Tracheids
and Vessel
Members
Fig. 26.6a, p. 420
Xylem:
Tracheids
and Vessel
Members
perforation
in the side
wall of
tracheid
A The end walls of tracheids
are tapered and unperforated.
Perforations in the side walls of
adjoining tracheids match up.
Fig. 26.6a, p. 420
Xylem:
Tracheids
and Vessel
Members
Fig. 26.6b, p. 420
Xylem:
Tracheids
and Vessel
Members
vessel member
B The thick, finely perforated end walls of dead
vessel member cells connect to make long
conducting tubes of xylem. The micrograph
shows three adjoining vessel members.
Fig. 26.6b, p. 420
Xylem:
Tracheids
and Vessel
Members
Fig. 26.6c, p. 420
Xylem:
Tracheids
and Vessel
Members
perforation
plate
C Vessel members vary in shape. A perforation
plate imparts strength to a junction where vessel
members meet, while also allowing water to flow
freely in through the xylem tube.
Fig. 26.6c, p. 420
Cohesion-Tension Theory
mesophyll
CohesionTension
Theory
vein
upper epidermis
1
stoma
vascular
xylem cambium phloem
2
root
vascular water
hair
cylinder molecule cortex cell soil
3
Fig. 26.7, p. 421
CohesionTension
Theory
Fig. 26.7a, p. 421
Cohesion-Tension Theory
mesophyll
vein
upper epidermis
stoma
Fig. 26.7b, p. 421
Cohesion-Tension Theory
xylem
vascular cambium
phloem
Fig. 26.7c, p. 421
Cohesion-Tension Theory
vascular cylinder
water
molecule
cortex
root hair cell
soil
Fig. 26.7d, p. 421
Cohesion-Tension Theory
mesophyll
vein
upper epidermis
1
stoma
vascular
xylem cambium phloem
2
root
vascular water
hair
cylinder molecule cortex cell soil
3
Stepped Art
Fig. 26.7, p. 421
ANIMATION: Transpiration
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Key Concepts
• Water Uptake and Movement Through Plants
• Certain specializations allow vascular plants to selectively
take up water and minerals through their roots
• Xylem transports absorbed water and solutes from roots to
other parts of the plant
ANIMATION: Tension-Cohesion Model
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Animation: Cohesion-Tension Theory
(or Water Transport)