Chapter 29 Part 3

© 2016 Pearson Education, Inc. Figure 29.15-2 Parasitic Plants Figure 29.15-2 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 © 2016 Pearson Education, Inc.

Carnivorous plants have adaptations for trapping insects and other small animals They are photosynthetic, but obtain nitrogen by killing and digesting prey © 2016 Pearson Education, Inc.

© 2016 Pearson Education, Inc. Figure 29.15-3 Carnivorous Plants Sundew Pitcher plants Venus flytraps Figure 29.15-3 Exploring unusual nutritional adaptations in plants (part 3: carnivorous plants) © 2016 Pearson Education, Inc.

© 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 © 2016 Pearson Education, Inc. 5

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 © 2016 Pearson Education, Inc. 6

© 2016 Pearson Education, Inc. Figure 29.16-1 Casparian strip Plasma membrane Apoplastic route Vessels (xylem) Apoplastic route Symplastic route Root hair Figure 29.16-1 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 © 2016 Pearson Education, Inc.

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 © 2016 Pearson Education, Inc. 8

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 © 2016 Pearson Education, Inc. 9

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 © 2016 Pearson Education, Inc. 10

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 © 2016 Pearson Education, Inc. 11

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 © 2016 Pearson Education, Inc. 12

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 © 2016 Pearson Education, Inc. 13

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 © 2016 Pearson Education, Inc. 14

© 2016 Pearson Education, Inc. Figure 29.19-1 Guard cells turgid/ Stoma open Guard cells flaccid/ Stoma closed Radially oriented cellulose microfibrils Cell wall Figure 29.19-1 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) © 2016 Pearson Education, Inc.

Changes in turgor pressure result primarily from the reversible uptake and loss of potassium ions (K+) by the guard cells © 2016 Pearson Education, Inc. 16

© 2016 Pearson Education, Inc. Figure 29.19-2 Guard cells turgid/ Stoma open Guard cells flaccid/ Stoma closed H2O H2O H2O H2O H2O K+ H2O H2O H2O H2O H2O Figure 29.19-2 Mechanisms of stomatal opening and closing (part 2: K+ ions) (b) Role of potassium ions (K+) in stomatal opening and closing © 2016 Pearson Education, Inc.

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 © 2016 Pearson Education, Inc. 18

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 © 2016 Pearson Education, Inc. 19

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 © 2016 Pearson Education, Inc. 20

© 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 29.20 Some xerophytic adaptations Old man cactus (Cephalocereus senilis) © 2016 Pearson Education, Inc.

© 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 © 2016 Pearson Education, Inc. 22

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 © 2016 Pearson Education, Inc. 23