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Plants #2

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Kendall Lake

on 17 May 2013

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Transcript of Plants #2

Plants #2 Plant Structure INTERACTIONS on two time scales long term: over time species can accumulate structural adaptations that enhance survival and reproduction
ex: stem is photosynthetic organ in desert plants to reduce water loss short term: individual plants respond to environment
ex: submerged abomba are feathery to extend surface area, have floating leaves plant architecture is continually shaped by genetically directed growth, along with fine tuning
basic structures reflect organisms that must inhabit and draw resources from two very different environments...
soil gives water and minerals, but air is the source of CO2! What to do?
TWO SYSTEMS: subterranean root and aerial shoot The Plant Systems Roots Shoots Organs Roots Stems Leaves would starve (no chloroplasts because there's no light) without sugar and imported nutrients
function: anchorage, absorption, storage, transport, hormones
hypocotyl, because it grows below the cotyledon meristomatic tissue is like our stem cells protects meristem cells as the root grows. worn and replaced quickly.
contains statoliths, which are starch grains that move in response to gravity and thus control root orientation absorption here because of extended surface area aka maturation, I suppose cells already have jobs cells are still growing Diagram Monocot vs. Dicot Roots Monocot has a fibrous root system, a mat of thin roots
major job: prevent soil erosion
roots extend exposure and anchor
water moves in between cells, is not filtered by membranes, but then it gets checked at the casparian strip Dicot typically taproot, with a long vertical root and many small lateral branch roots Adventitious Roots Root Types derived from any part other than radical/root tissue Arial roots Prop Roots Pneumatophores Haustoria Tuberous Roots derived from stem tissue
mostly for support, but can take up water
ex: ivy act as support for the plant, also absorb water and minerals
ex: corn, mangroves above salt water
walking palms can move up to one meter a year omg parasitic, attaches to host to absorb nutrients
may be derived from the roots or stem
ex: mistletoe, dodder a swollen root in which nutrients (usuall starch) are stored
dahlias, yams, sweet potatoes
NOT POTATOES, those are just tubers, which are made from stem tissue roots found in swampy areas where there isnt enough oxygen for the root to survive
grow towards surface and bend, forming a knob
almost hollow, allowing air to pass through living tissue
ex: cypress Root Transportation intracellular pathway: water and solutes cross barrier cell wall/membrane of epidermal cells and diffuse through the plasmodesmata before reaching xylem
extracellular: water and solutes move between cells until reaching the casparian strip before the xylem alternating system of nodes (where leaves are attached) and internodes (the stem segments in between nodes)
at each angle formed by the leaf and stem is an axillary or lateral bud, with the potential to form a vegetative brance
growth of a young shoot is usually concentrated at the apex, where there is a terminal bud with developing leaves and a compact series of nodes and internodes
depend on water and minerals absorbed by the roots Herbaceous Eudicot Stem Monocot Stem Specialization rhizomes: grow underground (horizontal), like ginger
stolons/runners: grow on the surface to asexually colonize a horizontal area by fragmentation (strawberries)
tubers: stem storage, swollen ends of rhizomes, like potatoes (the eyes are actually nodes)
bulbs: vertical underground shoots consisting mostly of the swollen bases of leaves that store food
cladophyll: flattened stem functioning as a leaf
thorns: protection Apical Dominance grows more strongly than side stems
apical bud produces hormone auxin which promotes growth but can also inhibit growth for lateral buds
pruning diverts auxin so there is less vertical, more horizontal different shapes
pine needles for cold/dry areas
often what we see as many leaves is actually one leaf diversity
cactus spines
tendrils (cucumbers) touch triggers elongation (thigmotropism)
hinged leaves (venus fly traps)
typically a flattened blade and the petiole
monocots = parallel veins, dicots = net veins Tissues ground dermal vascular all continuous throughout the plant in a leaf, the epidermis
generally a thin layer of tightly packed cells
includes stomata, which need to be open, which loses water
so, in the heat of summer, photosynthesis closes/stops
guard cells fill with water, the turgor pressue extends the thick part and curves the thin part to open it
cuticle protects xylem includes trachids (thicker) and/or vessel elements which are elongated cells that are dead at maturity
xylem is dead at maturity because water moves with capillary action
trachids and vessels have 2nd walls interrupted by pits, thinner regions
traechids: long, thin, tapered ends
has lignin, so for support as well as transport
vessel elements: short and squat phloem moves food, is alive
sieve tube members/elements
sieve plates have pores
companion cells have nucleus, may assist
plasmodesmata connects tubers to companions if it's not dermal or vascular, it's ground
in dicots, divided into pith (internal) and cortex (external)
photosynthesis, structure, and support Cells Parenchyma Collenchyma Schlerynchma cell walls thin and flexible
"typical" plant cells, least specialized
with exceptions, though, because highly specialized sieve-tubes are parenchyma
metabolic functions of the plant: photosynthesis
can be used for storage (starch) (fruit is usually parenchyma)
all cells start as parenchyma and later specialized
mature unspecialized parenchyma does not divide
most retain the ability to divide and differentiate under special conditions support the plant
very thick cell wall
dead at maturity
schlerids often pointy or jagged support the plant
thickening of the cell wall
tend to be as parts of vascular bundles or on the corners of angular stems HORMONES Auxin
promotes stem elongation and inhibits growth of lateral buds
elongates the darker side of the plants
produces a curving of the tip towards the light, a plant movement known as phototropism (+)
helps maintain apical dominance abscisic acid
promotes seed dormancy by inhibiting cell growth
involved in opening and closing stomata as leaves wilt ethylene gas produced by ripe fruits
why one ripe apple can spoil the whole bunch
used to ripen crops at the same time
spraying it on a field will cause all to ripen for harves Gibberelins Cytokenins promote cell elongation
not produced in stem tip promote cell division
used in growing areas, such as meristem at root tips Tropisms phototropism: light
geotropism: gravity
thigmotropism: touch
positive: towards
negative: away Plastids storage
chromoplasts: color
lukoplasts: starch (potatoesss)
statoliths contain starch that will get pulled down by gravity to trigger auxin Growth indeterminate: plants grow as long as they live
annuals complete in a year (wheat, corn, rice, wildflowers)
perennials complete once every two years (beets, carrots)
perennials take many years (trees, shrubs, some grasses) determinate: cease growing after a certain size (animals Primary Growth in length of the stem and root
Produces the basic tissue pattern in the stem and root
Involves mitosis of apical meristems found at the tip of a stem (in a bud) and/or root )protected by the root cap). 
Secondary growth in girth
secondary vascular tissues
mitosis of vascular cambium and cork cambium
vascular cambium: secondary vasculary
cork cambium: produces cork cells, which protect the stem and root from water loss, pathogens, and herbivorous insects. (makes wood!
Woody Twig Bark contains cork, cork cambium, and phloem
can be removed, but this hurts the tree :( due to lack or organic nutrient transport
cells impregnated with suberin, which impedes gas exchange, except at lenticels Wood secondary xylem that builds up after wear
vascular cambium dormant during winter
annual ring made of spring and summer wood
in older trees, inner annual rings (heartwood) no longer function in water transport
"earlywood" less dense, "latewood" stronger
boundary between late and early is the annual ring
exceptions: tropical trees, false rings from cold and drought
enoguh rain? wide ring. not? narrow ring
same region = semilar rings
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