1. Chapter 29
Part 3

2. © 2016 Pearson Education, Inc.
Figure
Parasitic Plants
Figure Exploring unusual nutritional adaptations in plants (part 2: parasitic plants)
Mistletoe, a
photosynthetic parasite
Dodder, a
nonphotosynthetic
parasite (orange)
Indian pipe, a
nonphotosynthetic
parasite of mycorrhizae
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3. Carnivorous plants have adaptations for trapping insects and other small animals
They are photosynthetic, but obtain nitrogen by killing and digesting prey
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4. © 2016 Pearson Education, Inc.
Figure
Carnivorous Plants
Sundew
Pitcher plants
Venus flytraps
Figure Exploring unusual nutritional adaptations in plants (part 3: carnivorous plants)
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5. © 2016 Pearson Education, Inc.
Concept 29.5: Transpiration drives the transport of water and minerals from roots to shoots via the xylem
Plants can move a large volume of water from their roots to shoots
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6. Absorption of Water and Minerals by Root Cells
Most water and mineral absorption occurs through root hairs located near root tips
After soil solution enters the roots, the extensive surface area of cortical cell membranes enhances uptake of water and selected minerals
The concentration of essential minerals is greater in the roots than in the soil because of active transport
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7. © 2016 Pearson Education, Inc.
Figure
Casparian strip
Plasma
membrane
Apoplastic
route
Vessels
(xylem)
Apoplastic
route
Symplastic
route
Root
hair
Figure Transport of water and minerals from root hairs to the xylem (part 1)
Symplastic
route
Epidermis
Endodermis
Vascular
cylinder
(stele)
Transmembrane
route
Cortex
The endodermis: controlled entry
to the vascular cylinder (stele)
Transport in the xylem
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8. The waxy Casparian strip of the endodermal wall blocks apoplastic transfer of minerals and water from the cortex to the vascular cylinder
Water and minerals must cross a selectively permeable plasma membrane before entering the vascular cylinder
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9. Pulling Xylem Sap: The Cohesion-Tension Hypothesis
According to the cohesion-tension hypothesis, transpiration and water cohesion pull water from shoots to roots
Xylem sap is normally under negative pressure, or tension
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10. Transpirational pull is generated when water vapor in the air spaces of a leaf diffuses down its water potential gradient and exits the leaf via stomata
As water evaporates, the air-water interface retreats farther into the mesophyll cell walls and becomes more curved
Due to the high surface tension of water, the curvature of the interface creates a negative pressure potential
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11. This negative pressure pulls water in the xylem into the leaf
The pulling effect results from the cohesive binding between water molecules
The transpirational pull on xylem sap is transmitted from leaves to roots
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12. Concept 29.6: The rate of transpiration is regulated by stomata
Leaves generally have large surface areas and high surface-to-volume ratios
These characteristics increase photosynthesis and increase water loss through stomata
Guard cells open and close the stomata to help balance water conservation with gas exchange
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13. Stomata: Major Pathways for Water Loss
About 95% of the water a plant loses escapes through stomata
Each stoma is flanked by a pair of guard cells, which control the diameter of the stoma by changing shape
Stomatal density is under genetic and environmental control
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14. Mechanisms of Stomatal Opening and Closing
Changes in turgor pressure open and close stomata
When turgid, guard cells bow outward and the pore between them opens
When flaccid, guard cells become less bowed and the pore closes
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15. © 2016 Pearson Education, Inc.
Figure
Guard cells turgid/
Stoma open
Guard cells flaccid/
Stoma closed
Radially oriented
cellulose microfibrils
Cell
wall
Figure Mechanisms of stomatal opening and closing (part 1: cell shape)
Vacuole
Guard cell
(a) Changes in guard cell shape and stomatal opening and closing (surface view)
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16. Changes in turgor pressure result primarily from the reversible uptake and loss of potassium ions (K+) by the guard cells
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17. © 2016 Pearson Education, Inc.
Figure
Guard cells turgid/
Stoma open
Guard cells flaccid/
Stoma closed
H2O
H2O
H2O
H2O
H2O K+
H2O
H2O
H2O
H2O
H2O
Figure Mechanisms of stomatal opening and closing (part 2: K+ ions)
(b) Role of potassium ions (K+) in stomatal opening and closing
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18. Stimuli for Stomatal Opening and Closing
Generally, stomata open during the day and close at night to minimize water loss
Stomatal opening at dawn is triggered by
Light
CO2 depletion
An internal “clock” in guard cells
All eukaryotic organisms have internal clocks; circadian rhythms are 24-hour cycles
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19. Drought stress can cause stomata to close during the daytime
The hormone abscisic acid (ABA) is produced in response to water deficiency and causes the closure of stomata
CO2 absorption is restricted when stomata are closed, causing photosynthesis to slow
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20. Adaptations That Reduce Evaporative Water Loss
Xerophytes are plants that have adaptations to arid climates, including
Thick cuticle and multilayered epidermis
Stomata recessed in crypts lined with hairs
Leaves reduced to spines or dropped for part of the year
Short life cycles completed during the rainy season
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21. © 2016 Pearson Education, Inc.
Ocotillo
(Fouquieria
splendens)
Oleander (Nerium oleander)
Figure 29.20
Thick cuticle
Upper epidermal tissue
100 mm
Trichomes
(“hairs”)
Crypt
Stoma
Lower epidermal
tissue
Figure Some xerophytic adaptations
Old man cactus
(Cephalocereus
senilis)
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22. © 2016 Pearson Education, Inc.
Concept 29.7: Sugars are transported from sources to sinks via the phloem
The products of photosynthesis are transported through phloem by the process of translocation
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23. Movement from Sugar Sources to Sugar Sinks
Phloem sap is an aqueous solution that is high in sucrose
It travels from a sugar source to a sugar sink
A sugar source is an organ that is a net producer of sugar, such as mature leaves
A sugar sink is an organ that is a net consumer or storer of sugar, such as a tuber or bulb
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