Transcript Chapter 29 - Fullfrontalanatomy.com

Chapter 29
The Working Plant
PowerPoint® Lectures for
Campbell Essential Biology, Fourth Edition
– Eric Simon, Jane Reece, and Jean Dickey
Campbell Essential Biology with Physiology, Third Edition
– Eric Simon, Jane Reece, and Jean Dickey
Lectures by Chris C. Romero, updated by Edward J. Zalisko
2010Pearson
PearsonEducation,
Education,Inc.
Inc.
©©2010
HOW PLANTS ACQUIRE AND TRANSPORT
NUTRIENTS
 Plants obtain
 Carbon dioxide (CO2) from the air
 Water (H2O) and minerals (inorganic ions) from the soil
 Plants produce sugars via photosynthesis using
 CO2
 H2O
 A plant constructs all the other organic materials it needs using these sugars
and minerals.
 A plant’s essential elements are chemical elements, obtained from its
environment, and needed to complete its life cycle.
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CO2
Minerals
(inorganic
ions)
H2O
Figure 29.1
Figure 29.2
H2O
Transpiration
(regulated by guard
cells surrounding stomata)
Cohesion and adhesion in xylem
(cohesion of H2O molecules to
each other and adhesion of H2O
molecules to xylem cell walls)
H2O
Water uptake
via root hairs
Figure 29.UN03
 Of the essential elements
 9 are macronutrients, required in relatively large amounts
 8 are micronutrients, which plants require in relatively small amounts
 Six macronutrients, carbon, oxygen, hydrogen, nitrogen, sulfur, and
phosphorus, make up almost 98% of a plant’s dry weight.
 Calcium, potassium, and magnesium make up another 1.5% of a plant’s dry
weight.
 What does a plant do with macronutrients?
 Carbon, oxygen, and hydrogen are the basic ingredients of a plant’s organic
compounds.
 Nitrogen is a component of

All nucleic acids

All proteins

ATP

Chlorophyll

Many plant hormones
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 Sulfur is a component of most proteins.
 Phosphorus is a major component of
 Nucleic acids
 Phospholipids
 ATP
 Eight micronutrients
 Are required by all plants
 Make up the remaining 0.5% of a plant’s dry weight
 Micronutrients are
 Recycled, and therefore
 Needed in small amounts
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Fertilizers
 The quality of soil affects
 The growth of plants
 Their nutritional value to organisms that eat them
 Nitrogen shortage is the most common nutritional problem for plants.
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Figure 29.3
 Fertilizers are compounds given to plants via the soil to promote the plants’
growth.
 There are two types of fertilizers:
 Inorganic fertilizers that contain simple, inorganic minerals
 Organic fertilizers composed of chemically complex organic matter
 One source of organic fertilizer is compost, a soil-like mixture of decomposed
organic matter created by microbes, fungi, and animals that break down dead
organic matter.
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Figure 29.4
 Organic farming
 Uses compost and other organic fertilizers produced on a large scale
 Uses few or no synthetic pesticides
 Intends to build a sustainable agricultural system
 Is one of the fastest-growing segments of agriculture
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From the Soil into the Roots
 A plant uses its roots to absorb water and essential nutrients from the soil.
 Root hairs
 Are extensions of epidermal cells
 Dramatically increase the surface area available for absorption
 Root Growth: Here and Here
 Mineral absorption by roots Here
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Low sugar
concentration
Sink cell
Source cell
Sugar
Sugar
High sugar
concentration
Figure 29.UN04
Figure 29.5
N2
Air
Soil
Root
Nitrogen-fixing
bacteria
NH4+
(ammonium)
Nitrifying
bacteria
NO3–
(nitrate)
Ammonifying
bacteria
Figure 29.UN02
 All substances that enter a plant root
 Must be dissolved in water
 Pass through the selectively permeable plasma membranes of root cells
 Many plants form mycorrhizae, symbiotic associations with fungi that increase the
absorptive surface area of the roots.
 Most plants rely on bacteria to supply them with usable nitrogen in the form of
 Ammonium ions (NH4+) or
 Nitrate ions (NO3–)
 Three types of soil bacteria play an essential role in supplying plants with
nitrogen.
 Nitrogen-fixing bacteria convert atmospheric N2 to ammonium, a process called
nitrogen fixation.
 Ammonifying bacteria add to the soil’s supply of ammonium by decomposing
organic matter.
 Nitrifying bacteria convert soil ammonium to nitrate.
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SEM
Root
Fungal
filament
Mycorrhiza
Figure 29.6
Air
N2
N2
Soil
Nitrogen-fixing
bacteria
NH4+
NH4+
(ammonium)
Soil
Ammonifying
Organic bacteria
material
Nitrifying
bacteria
NO3–
(nitrate)
Root
Figure 29.7
Root Nodule Bacteria and Nitrogen
 Legumes
 Include peas, beans, and peanuts
 Have their own nitrogen-fixing bacteria in root nodules that produce ammonium
 To thrive, a plant must be able to transport
 Water
 Dissolved ions from its roots to the rest of the plant
 Plants transport xylem sap from the roots to the tips of the leaves through
vertical xylem tubes
 Transpiration, the loss of water vapor from the leaves of a plant by
evaporation
 Occurs through the stomata of leaves
 Pulls xylem sap up the plant against gravity
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TEM
Shoot
Roots
Root nodule bacteria
Bacteria
within
vesicle
Nodules
Root nodules
Figure 29.8
 Transpiration relies on two properties of water.
 Cohesion is the sticking together of molecules of the same kind.
 Adhesion is the sticking together of molecules of different kinds.
 The ascent of xylem sap is called the transpiration-cohesion-tension
mechanism.
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Leaf
Xylem sap
Mesophyll cells
Air space within leaf
Stoma
Water molecule
Outside air
Transpiration
Flow of water
Adhesion
Stem
Water
molecule
Cohesion and
adhesion in the xylem
Xylem
cells
Cell wall
Cohesion,
by hydrogen
bonding
Xylem sap
Root
Root hair
Soil particle
Water
Water uptake from soil
Figure 29.9-3
The Regulation of Transpiration by
Stomata
 Transpiration
 Helps move xylem sap through a plant
 Can cause plants to lose large amounts of water
 Plants adjust their transpiration rates to changing environmental conditions.
 Stomata are usually open during the day, which
 Allows CO2 to enter the leaf from the atmosphere
 Keeps photosynthesis going when sunlight is available
 At night, there is no light for photosynthesis, therefore no need for CO2, and
the stomata are closed.
 Stomata are opened and closed by changes in the shape of the two guard
cells flanking each stoma.
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Guard cells
CO2
Stoma open during
daytime
Stoma closed at night
H2O
Figure 29.10
The Transport of Sugars
 Phloem sap transports
 Sugars a plant makes by photosynthesi,
 Inorganic ions
 Amino acids
 Hormones
 Phloem sap moves in various directions, from a sugar source, where sugar is
produced, to a sugar sink, where sugar is stored or consumed.
 Phloem sap moves from a sugar source to a sugar sink by the pressure-flow
mechanism.
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Flow of
phloem
sap
Foodconducting
cell
TEM
Opening
between cells
Foodconducting
cell
Figure 29.11
High sugar
concentration
Phloem
Xylem
Source cell
Sugar
source
Sugar
e
Sugar
sink
H2O
Sink cell
Sugar
H2O
Low sugar
concentration
Figure 29.12
PLANT HORMONES
 A hormone is a chemical signal that
 Is produced in one part of the body
 Is transported to other parts
 Acts on target cells to change their functions
 Hormones control plant growth and development by affecting the
 Division
 Elongation
 Differentiation of cells
 Plant biologists have identified five major types of plant hormones.
 Auxins are
 A group of related hormones
 Responsible for a wide range of growth and development effects in plants
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Table 29.1
Phototropism and Cell Elongation
 Phototropism is
 The directional growth of a plant shoot in response to light
 Caused by the elongation of cells on the darker side of the stem
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Figure 29.13
Shaded
side of
shoot
Light
Illuminated side of shoot
Figure 29.14
Control
Tip
removed
Tip covered
by opaque
cap
Tip covered
by transparent cap
Base covered
by
opaque shield
Light
Figure 29.15
The Action of Auxins
 The chemical responsible for phototropism is a hormone called auxin.
 An uneven distribution of auxin on each side of a shoot causes
 Higher auxin concentrations in the cells on the dark side
 Cells on the dark side to elongate
 The shoot to bend
 The use of synthetic plant hormones allows more food to be produced at
lower cost.
 One widely used herbicide is a weed killer that
 Is a synthetic auxin that disrupts the normal balance of hormones that regulate plant
growth
 Affects monocots more than dicots
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Ethylene
 Ethylene is a hormone that is released as a gas that triggers a variety of aging
responses in plants, including
 Fruit ripening
 Dropping of leaves
 Fruit ripening is
 Triggered by a burst of ethylene production in the fruit
 Spread from fruit to fruit by ethylene gas
 Some fruits ripen faster if stored in a plastic bag that accumulates ethylene
gas.
 Stored apples are often flushed with CO2, which inhibits the action of
ethylene.
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Banana alone
Banana + ethylenereleasing orange
Banana + beaker of an
ethylene-releasing chemical
Figure 29.16
Leaf Drop
 The loss of leaves in autumn is affected by ethylene.
 Leaf drop is triggered by environmental stimuli that
 Cause a change in the balance of ethylene and auxin
 Weaken cell walls in a layer of cells at the base of the leaf stalk
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Cytokinins
 Cytokinins
 Are a group of closely related hormones that act as growth regulators that promote
cell division
 Are produced in actively growing tissues
 Counter the inhibitory effects of auxin, resulting in complex growth patterns in most
plants
 A combination of gibberellins and auxins can
 Influence fruit development
 Make apples, currants, and eggplants develop without pollination and seed
production
 Make seedless grapes grow larger and farther apart in a cluster
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Untreated
Treated with
gibberellins
Figure 29.17
Abscisic Acid
 Abscisic acid
 Generally slows down growth
 Can inhibit seed germination, allowing seeds to go dormant
 Some desert plants remain dormant until a downpour of rain
 Washes out abscisic acid
 Allows the seeds to germinate when water is available
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Figure 29.18
RESPONSE TO STIMULI
 Plants can respond to physical stimuli from the environment, including
 Light
 Touch
 Gravity
 Tropisms are directed growth responses that cause parts of a plant to grow
 Toward or
 Away from a stimulus
 Phototropism is the directional growth of a plant shoot in response to light.
 Thigmotropism
 Is a response to touch
 Occurs when a pea plant tendril coils around a string or wire it touches for support
 Gravitropism
 Is a response to gravity
 Occurs when

Roots grow down

Shoots grow upward
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TROPISMS
(directed growth responses)
Phototropism
Thigmotropism
Gravitropism
Figure 29.19
Figure 29.19b
Figure 29.19c
Photoperiod
 Light
 Provides energy for photosynthesis
 Directs growth
 Regulates a plant’s life cycle, including

Flowering

Seed germination

The onset and ending of dormancy
 A photoperiod is the relative lengths of day and night.
 Plants whose flowering is triggered by photoperiod fall into two groups:
 Long-night plants
 Short-night plants
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Flowering occurs only
when the plant is
exposed to a continuous
dark period exceeding a
critical length.
Short-night plants
Flowering occurs when
the night length is shorter
than a critical length.
The continuity of darkness is
important. The long-night
plant will not blossom if the
darkness is interrupted by
even a flash of light.
24
Darkness
Time (hours)
Flash of Light
Flowering can be
induced in a short-night
plant by a flash of
light during the night.
Critical night length
Long-night plants
Light
0
Figure 29.20
 Florists apply knowledge of the photoperiod of particular plants to bring us
flowers out of season.
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Evolution Connection:
Plants, Frogs, and People
 Plants rely on organisms from two other kingdoms to help acquire nutrients:
 Soil bacteria
 The fungi of mycorrhizae
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 Nearly all animals depend on plants or other photosynthetic organisms for
food.
 Consider a frog.
 Tadpoles depend on algae and aquatic plants for food.
 Adults eat a wide variety of insects.
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Figure 29.21
 One of biology’s overarching themes is the interrelatedness of organisms.
 Animals depend on other animals and plants.
 Plants depend on animals and fungi.
 All eukaryotic life depends on prokaryotes.
 This interdependency reminds us once again that it is impossible to separate
ourselves from all of the living creatures that share the biosphere.
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Figure 29.UN01