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Plant Anatomy Chapter 35
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Basic plant anatomy 1 root root tip root hairs
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1 Roots Roots anchor plant in soil, absorb minerals & water, & store food fibrous roots (1) mat of thin roots that spread out monocots tap roots (2) 1 large vertical root also produces many small lateral, or branch roots dicots root hairs (3) increase absorptive surface area 2 3
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Basic plant anatomy 2 root shoot (stem)
fungi at tips of the roots Mycorrhizae -Symbiotic relationship shoot (stem) buds terminal or apical buds-located at the top axillary buds-located at the V formed b/t leaf and stem
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stolons (strawberries)
Modified shoots stolons (strawberries) rhizome (ginger) tuber (potato) bulb (onion)
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Leaves Function of leaves photosynthesis gas exchange transpiration
energy production CHO production gas exchange transpiration simple vs. compound
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Putting it all together
Obtaining raw materials sunlight leaves = solar collectors CO2 stomates = gas exchange H2O uptake from roots nutrients
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Plant TISSUES Dermal Ground Vascular epidermis (“skin” of plant)
single layer of tightly packed cells that covers & protects plant Ground bulk of plant tissue photosynthetic mesophyll, storage Vascular transport system in shoots & roots xylem & phloem
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Plant CELL types in plant tissues
Parenchyma “typical” plant cells = least specialized photosynthetic cells, storage cells tissue of leaves, stem, fruit, storage roots Collenchyma unevenly thickened primary walls support Sclerenchyma very thick, “woody” secondary walls rigid cells that can’t elongate dead at functional maturity If I’d only had triplets!
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Xylem and Phloem Xylem- water conducting cells. xylem vessels- found mostly in angiosperms have pits for water movement. xylem tracheids- long thin cells strengthen with lignin
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Structure–Function again!
Vascular tissue vessel elements Xylem move water & minerals up from roots dead cells at functional maturity only cell walls remain need empty pipes to efficiently move H2O transpirational pull vessel element dead cells Aaaah… Structure–Function again! tracheids
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Phloem: food-conducting cells
carry sugars & nutrients throughout plant sieve tube companion cell sieve plate plasmodesmata living cells
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Phloem: food-conducting cells
sieve tube elements & companion cells
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Structure–Function again!
Aaaah… Structure–Function again! Phloem Living cells at functional maturity cell membrane, cytoplasm control of diffusion lose their nucleus, ribosomes & vacuole more room for specialized transport of liquid food (sucrose) Cells sieve tubes sieve plates — end walls — have pores to facilitate flow of fluid between cells companion cells nucleated cells connected to the sieve-tube help sieve tubes
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Plant Growth Chapter 35
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Life Cycle of Plants Annuals- in one year Ex:Wildflowers, crops
Biennials- completed in 2 years Ex: radishes and carrots Perennials- continues for many years Ex. Trees
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Growth in Plants Specific regions of growth: meristems
stem cells: perpetually embryonic tissue regenerate new cells apical shoot meristem growth in length primary growth apical root meristem lateral meristem growth in girth secondary growth
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Apical meristems shoot root
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Root structure & growth
protecting the meristem
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protecting the meristem
Shoot growth protecting the meristem Young leaf primordium Apical meristem Older leaf primordium Lateral bud primordium Vascular tissue
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Growth in woody plants Woody plants grow in height from tip
Primary xylem Growth in woody plants Woody plants grow in height from tip primary growth apical meristem Woody plants grow in diameter from sides secondary growth lateral meristems vascular cambium makes 2° phloem & 2° xylem cork cambium makes bark Primary phloem Epidermis Lateral meristems Secondary xylem Primary phloem Primary xylem Secondary phloem Annual growth layers Bark
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Why are early & late growth different?
Vascular cambium Phloem produced to the outside Xylem produced to the inside bark phloem cork cambium xylem late vascular cambium early last year’s xylem
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Woody stem How old is this tree? cork cambium vascular cambium late
early 3 2 1 xylem phloem bark
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Secondary Growth produced by the vascular cambium
xylem After one year of growth After two years phloem Vascular cambium X P C
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Plant hormones Ch:39 auxin gibberellins abscisic acid ethylene
and more…
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Auxin (IAA) Effects controls cell division & differentiation
phototropism growth towards light asymmetrical distribution of auxin cells on darker side elongate faster than cells on brighter side apical dominance
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Gibberellins Family of hormones Effects
over 100 different gibberellins identified Effects stem elongation fruit growth seed germination plump grapes in grocery stores have been treated with gibberellin hormones while on the vine
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Abscisic acid (ABA) Effects slows growth seed dormancy
high concentrations of abscisic acid germination only after ABA is inactivated or leeched out survival value: seed will germinate only under optimal conditions light, temperature, moisture
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One bad apple spoils the whole bunch…
Ethylene Hormone gas released by plant cells Effects fruit ripening leaf drop like in Autumn apoptosis One bad apple spoils the whole bunch…
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Fruit ripening Adaptation Mechanism
hard, tart fruit protects developing seed from herbivores ripe, sweet, soft fruit attracts animals to disperse seed Mechanism triggers ripening process breakdown of cell wall softening conversion of starch to sugar sweetening positive feedback system ethylene triggers ripening ripening stimulates more ethylene production
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Apoptosis in plants Many events in plants involve apoptosis
What is the evolutionary advantage of loss of leaves in autumn? Many events in plants involve apoptosis response to hormones ethylene auxin death of annual plant after flowering senescence differentiation of xylem vessels loss of cytoplasm shedding of autumn leaves The loss of leaves each autumn is an adaptation that keeps deciduous trees from desiccating during winter when the roots cannot absorb water from the frozen ground. Before leaves abscise, many essential elements are salvaged from the dying leaves and are stored in stem parenchyma cells. These nutrients are recycled back to developing leaves the following spring. Fall color is a combination of new red pigments made during autumn and yellow and orange carotenoids that were already present in the leaf but are rendered visible by the breakdown of the dark green chlorophyll in autumn. Photo: Abscission of a maple leaf. Abscission is controlled by a change in the balance of ethylene and auxin. The abscission layer can be seen here as a vertical band at the base of the petiole. After the leaf falls, a protective layer of cork becomes the leaf scar that helps prevent pathogens from invading the plant (LM).
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