Growth, morphogenesis, and differentiation produce the plant body

●Morphogenesis is the development of body form and organization ●The three developmental processes of growth, morphogenesis, and cellular differentiation act in concert to transform the fertilized egg into a plant

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Fig. 35-29

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●The vascular tissue system carries out long-distance transport of materials between roots and shoots●The two vascular tissues are xylem and phloem●Xylem conveys water and dissolved minerals upward from roots into the shoots●Phloem transports organic nutrients from where they are made to where they are needed

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Xylem has NEGATIVE water potential Phloem has POSITIVE water potential

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Aquaporins: Facilitating Diffusion of Water

●Aquaporins are transport proteins in the cell membrane that allow the passage of water●The rate of water movement is likely regulated by phosphorylation of the aquaporin proteins

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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, CO

2

depletion, and an internal “clock” in guard cells●All eukaryotic organisms have internal clocks; circadian rhythms are 24-hour cycles

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Bulk Flow by Positive Pressure: The Mechanism of Translocation in Angiosperms

●In studying angiosperms, researchers have concluded that sap moves through a sieve tube by bulk flow driven by positive pressure

Animation: Translocation of Phloem Sap in Summer

Animation: Translocation of Phloem Sap in Spring

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4

Fig. 36-20

3

2

1

1

2

34

Vessel(xylem)

Sieve tube(phloem)

Source cell(leaf) Loading of sugar

Uptake of water

Unloading of sugar

Water recycled

Sink cell(storageroot)

Sucrose

H2O

H2O

Bu

lk f

low

by

neg

ativ

e p

ress

ure

H2O

Sucrose

Bu

lk f

low

by

po

siti

ve p

ress

ure

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Biological Clock Regulation by the Hypothalamus

●The hypothalamus also regulates circadian rhythms such as the 24 Hour sleep/wake cycle All eukaryotic organisms have internal clocks●Biological clocks usually require external cues to remain synchronized with environmental cycles

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The Diencephalon

The hypothalamus regulates homeostasis and basic survival behaviors such as feeding, fighting, fleeing, and reproducing

Fig. 49-UN3

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Fungi and Plant Nutrition

●Mycorrhizae are mutualistic associations of fungi and roots●The fungus benefits from a steady supply of sugar from the host plant●The host plant benefits because the fungus increases the surface area for water uptake and mineral absorption●Mycorrizal relationships are common and might have helped plants to first colonize land

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Agricultural and Ecological Importance of Mycorrhizae

●Farmers and foresters often inoculate seeds with fungal spores to promote formation of mycorrhizae●Some invasive exotic plants disrupt interactions between native plants and their mycorrhizal fungi

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●In the late 1800s, Charles Darwin and his son Francis conducted experiments on phototropism, a plant’s response to light●They observed that a grass seedling could bend toward light only if the tip of the coleoptile was present●They postulated that a signal was transmitted from the tip to the elongating region

Video: Phototropism

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Fig. 39-5b

RESULTS

Light

Tipremove

d

Darwin and Darwin: phototropic response only when tip is illuminated

Tip covered

by opaquecap

Tip covered by

trans-parentcap

Site ofcurvatur

e covered

by opaque shield

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Control of Cell Division and Differentiation

●Cytokinins are produced in actively growing tissues such as roots, embryos, and fruits●Cytokinins work together with auxin to control cell division and differentiation

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A Survey of Plant Hormones

●In general, hormones control plant growth and development by affecting the division, elongation, and differentiation of cells●Plant hormones are produced in very low concentration, but a minute amount can greatly affect growth and development of a plant organ

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Gibberellins

●Gibberellins have a variety of effects, such as stem elongation, fruit growth, and seed germination

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Fig. 39-10

a.Gibberellin-induced stem growth

(b) Gibberellin-induced fruit growth

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●Circadian rhythms are cycles that are about 24 hours long and are governed by an internal “clock”●Circadian rhythms can be entrained to exactly 24 hours by the day/night cycle●The clock may depend on synthesis of a protein regulated through feedback control and may be common to all eukaryotes

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Fig. 39-20

Noon Midnight

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●Unit 6C35 45&screen shot, 113&130, C36 82&(C49 52/53/54), 46&47, 98&99C37 57&66●C38 (C11)&screenshot●C39 20&21, 23&26, 38&45, 80&81

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