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Chapter 35: Plant Structure and Growth AP Biology 2006-2007 Basic plant anatomy 1 root AP Biology root tip root hairs 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) 2 increase absorptive surface area AP Biology 3 Basic plant anatomy 2 root root tip root hairs shoot (stem) nodes internodes buds terminal or apical buds axillary buds flower buds & flowers AP Biology Modified shoots stolons (strawberries) AP Biology tuber (potato) rhizome (ginger) bulb (onion) Basic plant anatomy 3 root root tip root hairs shoot (stem) nodes internodes buds terminal or apical buds axillary buds flower buds & flowers leaves AP Biology mesophyll tissue veins (vascular bundles) Leaves Function of leaves photosynthesis energy production CHO production gas exchange transpiration AP Biology simple vs. compound Modified leaves tendrils (peas) AP Biology succulent leaves spines (cacti) colored leaves (poinsetta) AP Biology Interdependent systems Both systems depend on the other roots depend on sugars produced by photosynthetic leaves shoots depend on water & minerals absorbed from the soil by roots AP Biology sugars water & minerals Plant TISSUES Dermal epidermis (“skin” of plant) single layer of tightly packed cells that covers & protects plant Ground bulk of plant tissue photosynthetic mesophyll, storage Vascular AP Biology transport system in shoots & roots xylem & phloem 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 AP Biology very thick, “woody” secondary walls support rigid cells that can’t elongate dead at functional maturity If I’d only had triplets! Parenchyma Parenchyma cells are unspecialized, thin, flexible & carry out many metabolic functions AP Biology all other cell types in plants develop from parenchyma Collenchyma Collenchyma cells have thicker primary walls & provide support AP Biology help support without restraining growth remain alive in maturity the strings in celery stalks are collenchyma Sclerenchyma Thick, rigid cell wall lignin (wood) cannot elongate mostly dead at maturity Cells for support xylem vessels xylem tracheids fibers rope fibers sclereids nutshells seed coats grittiness in pears AP Biology vessel elements Xylem vessel element Vascular tissue move water & minerals up from roots dead cells at functional maturity only cell walls remain need empty pipes to efficiently move H2O transpirational pull dead cells Aaaah… Structure–Function again! tracheids AP Biology Phloem: food-conducting cells carry sugars & nutrients throughout plant sieve tube companion cell sieve plate plasmodesmata AP Biology living cells Phloem: food-conducting cells sieve tube elements & companion cells AP Biology Phloem Aaaah… Structure–Function again! 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 AP Biology Vascular tissue in stems dicot trees & shrubs AP Biology collect annual rings monocot grasses & lilies Vascular tissue in roots: dicot phloem AP Biology xylem Vascular tissue in roots: monocot xylem phloem AP Biology Putting it all together Obtaining raw materials sunlight leaves = solar collectors CO2 stomates = gas exchange H2O uptake from roots nutrients uptake from roots AP Biology Phloem sieve tubes AP Biology sieve plate Plant Growth AP Biology Growth in Animals Animals grow throughout the whole organism AP Biology many regions & tissues at different rates 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 growth in length primary growth lateral meristem growth in girth secondary growth AP Biology Apical meristems AP Biology shoot root Root structure & growth AP Biology protecting the meristem Shoot growth Apical bud & primary growth of shoot region of stem growth axillary buds “waiting in the wings” protecting the meristem Young leaf primordium Apical meristem Older leaf primordium Lateral bud primordium AP Biology Vascular tissue Primary xylem Growth in woody plants Primary phloem Woody plants grow in Epidermis height from tip Lateral meristems primary growth apical meristem Woody plants grow in diameter from sides secondary growth lateral meristems Primary phloem Secondary phloem Secondary Primary xylem xylem vascular cambium makes 2° phloem & 2° xylem cork cambium makes bark Annual AP Biology growth layers Bark Secondary growth Secondary growth growth in diameter thickens & strengthens older part of tree cork cambium makes bark growing ring around tree vascular cambium makes xylem & phloem growing ring around tree AP Biology Vascular cambium Why are early & late growth different? Phloem produced to the outside Xylem produced to the inside bark cork cambium phloem xylem vascular cambium AP Biology late early last year’s xylem cork cambium Woody stem How old is this tree? vascular cambium late early 3 2 1 xylem phloem AP Biology bark Tree trunk anatomy tree girdling What does girdling do to a tree? AP Biology Aaaargh! Murderer! Arborcide! Where will the carving be in 50 years? AP Biology Plant hormones auxin gibberellins abscisic acid ethylene and more… AP Biology 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 AP Biology apical dominance Gibberellins Family of hormones over 100 different gibberellins identified Effects stem elongation fruit growth seed germination AP Biology plump grapes in grocery stores have been treated with gibberellin hormones while on the vine 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 AP Biology Ethylene Hormone gas released by plant cells Effects fruit ripening leaf drop like in Autumn apoptosis One bad apple spoils the whole bunch… AP Biology Fruit ripening Adaptation 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 AP Biology Apoptosis in plants 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 AP Biology shedding of autumn leaves What is the evolutionary advantage of loss of leaves in autumn?