Plant Homeostasis Structure and Function. Flowers Organs of sexual reproduction in plants.
Chapter 31: Plant Structure, Reproduction and Development.
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Transcript of Chapter 31: Plant Structure, Reproduction and Development.
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Chapter 31:Plant Structure, Reproduction
and Development
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Angiosperms-Most diverse category of plants.-Flowers provide a highly effective mode for pollination.-Vascular tissue allows for transportation of water.-Subdivided into monocots and dicots.
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Monocots/Dicots
• Represent two branches of angiosperm evolution.
• Are characterized by different patterns of vascular tissue distribution in leaves and stems, number of seed leaves, flower structure, and root structure.
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• Leaf - photosynthesis
• Stem - transport
• Root - absorption (and transport…)
• Flower - reproduction (not shown…)
Plant Structures/Functions
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The Plant Body
• The body of angiosperms breaks down into roots and shoots.
• Shoots can be further subdivided into leaves and stems.
• All plant structures fit into these three categories: most flowers and thorns are modified leaves, runners and tubers are modified stems, etc.
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Root Cross SectionCortex
Endodermis
Pericycle
Xylem
Phloem
Downloaded 4/10/02 from http://www.puc.edu/Faculty/Gilbert_Muth/phot0167.jpg
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• Water must move from the epidermis, through root tissues, and into the xylem.
• Water may take a cellular route, or the route between the cells...
Water Uptake
Xylem
Epidermis Endodermis
Cortex Pericycle
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• Cellular route = symplast• Non-cellular route = apoplast• The waterproofing in the endodermis is called the
Casparian Strip
Water UptakeEpidermis Endodermis
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Tissue Systems
• Angiosperms contain three tissue systems. • The epidermis covers plant surfaces, provides
protection for the inner tissues, and helps to regulate the flow of materials into and out of the plant.
• Ground tissue plays a role in storage, support, and photosynthesis.
• Vascular tissue…
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Vascular tissue:• Vascular tissue allowed plants develop in
many new terrestrial environments. It carries materials through the plant body.
• Two types: Xylem and Phloem.• Xylem: Carries water up into the plant,
composed of dead trachied and vessel element cells.
• Phloem: Carries food from sugar sources to sugar sinks, compose of living cells.
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Transpiration
• Allows water to be transported through the xylem, up from the roots and to the rest of the plant.
• Depends on the cohesive and adhesive properties of water.
• Cohesion: Molecules stick to like molecules.• Adhesion: Molecules stick to molecules that
are different from them.
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Remember how hydrogen bonding held water molecules to each other..
Hydrogen Bonding
…and water molecules to the sides of their container (e.g. xylem tubes)
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Transpiration
• Water exists as a continuous column in the xylem vessels. It is pulled up through the xylem as water exits the leaves through openings called stomata (stoma is Latin for mouth).
• Action is similar to that of a straw.• How is the vascular tissue of plants similar to
blood vessels in animals? How is it different?
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Xylem Tissue• Consists of Tracheids & Vessel Elements• When matured, these cells are dead (just
cell wall).• Plant roots pump inorganic ions into xylem.• Water moves into xylem via osmosis
( Results in root Pressure)• END RESULT – Xylem sap moves upward.
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Stomata
• Openings found throughout the epidermis of the leaf.
• Allow for exchange of gases with the outside environment.
• Major contributor to water loss in plants.• Guard cells close stoma to minimize loss of
water. Usually close stomata at night.
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Guard Cells
• Control opening of stomata: Open during day and Closed @ night–Why open during day???
–Sunlight stimulates uptake of K+–Decreased of [CO2]–Bio Clock (rhythm)
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Guard Cells
• Control opening of stomata: Open during day and Closed @ night–Why closed @ night???–No light, therefore no
photosynthesis, therefore no need to take up CO2
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Figure 32.4
• Stoma Open:–Gain K+–Water then enters via osmosis–Vacuole in guard cells swell – Turgid–Cell wall “buckles” away from
companion cell
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Figure 32.4
• Stoma Closed:–Lose K+–Water exits via osmosis–Vacuole in guard cells shrink –
Flaccid–Cell wall “returns” towards
companion cell
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Open/closing of stomate
• Guard cells on the left are full of water• Stomate is open
Guard cell
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SEM micrograph of stomate
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Water Loss
• Several mechanisms for reducing water loss have evolved in plants.
• Cuticle: waxy coating outside of epidermis, helps to seal in water.
• C-4 plants: Separate the photosynthetic process in space using compartmentalization.
• CAM plants: Separate the steps of photosynthesis in time.
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Nitrogen (Macronutrient)
• Why Nitrogen????• Required for plant growth & normal
processes.• Deficiencies = changes in plant color
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N2 Fixation
• Plants cannot use Nitrogen from atmosphere (N2).
• For absorption from soil Nitrogen must be converted to NH4+ or NO3
• Need soil bacteria to perform this conversion.