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BIOL 1108: Test 2
What are the closest relatives to plants
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charophytes (green algae)
Parts: blade, stipe, and holdfast (similar to leaves, stems, and roots, but are mostly homoplasies)
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Similarities between plants and charophytes
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rosette-shaped cellulose-synthesizing complexes - cells of both have circular proteins in plasma membrane
peroxisome enzymes - contain enzymes that help minimize loss of organic products to photorespiration
structure of flagellated sperm in plants that have it closely resembles sperm of charophytes
formation of phragmoplast in dividing cells
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Four plant groups
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1. nonvascular plants (bryophytes)
2. seedless vascular
3. gymnosperms
4. angiosperms
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When did land plants originate?
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~475 million years ago
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When did vascular plants originate?
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~420 million years ago
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When did seed plants originate?
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~360 million years ago (or ~305 mya according to book)
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Why are nonvascular plants found in damp, shady locations?
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need water for fertilization
can't carry water to plant structures without vascular tissue
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Within the plant types, which two are the most closely related?
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angiosperms and gymnosperms
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What are the three basic plant organs?
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roots
stems
leaves
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Roots
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anchors plant in soil
absorbs minerals and water
stores carbohydrates
taproot and lateral (branch) roots
root hairs increase SA, primary site of absorption (short lived and constantly replaced)
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Stem
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nodes: points where leaves are attached
internodes: stem segments between nodes
auxillary buds and apical buds; apical dominance
do perform photosynthesis
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Leaves
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in most plants, the main photosynthetic organ
blade and petiole (joins leaf to stem at node)
simple leaves, compound leaves, doubly compound leaves
veins - vascular tissue
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Dermal tissue
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the plant's outer protective covering
first line of defense against physical damage and pathogens
called epidermis in non-woody plants
called peridern in woody plants
cuticle - waxy coating on surface prevents water loss
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Vascular tissue
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carries out long distance transport of materials between root and shoot systems
xylem conducts water and dissolve minerals upward from roots
phloem transports sugars from source to roots and sites of growth
stele: collective vascular tissue of a root or stem
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Ground tissue
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tissues that are neither vascular nor dermal
when external to vascular tissue: cortex
when internal to vascular tissue: pith
various functions, such as storage, photosynthesis, and support
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Primary cell wall
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fully permeable membrane
permits passage of small molecules and small proteins
key nutrients, especially water and CO2 are distributed throughout plant from cell wall to cell wall in apoplastic flow [apoplast is the continuum of cell walls plus extracellular space]
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secondary cell wall
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a thick layer formed inside primary cell wall after the cell is fully grown
not in all cell types
in xylem, secondary wall contains lignin which strengthens and waterproofs the wall
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Cuticle
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waxy coating on the epidermal surface which helps prevent water loss
evolution of this has allowed for plants to live on land
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Microphyll
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small spine shaped leaves
may have originated from sporangia
supported by single, unbranched strand of vascular tissue
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Megaphylls
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leaves with highly branched vascular systems
may have evolved from the fusion of branched stems
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Root hairs |
increase surface area for nutrient absorption
absorption of water and inorganic nutrients
anchoring the plant body to the ground
function in storage of food and nutrients
in response to the concentration of nutrients, roots also synthesize cytokinin, which acts as a signal as to how fast the shoots can grow
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How do land plants prevent dehydration?
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cuticle to reduce water loss
uptake and distribution with vascular tissue
stomata to regulate loss
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What are the three basic cell types in plants?
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parenchyma
collenchyma
sclerenchyma
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Parenchyma |
-form:
cell membrane
primary cell wall: cellulose, thin and flexible, water and gas permeable
-function
metabolic activity and storage
generally alive at maturity and many retail ability to divide and differentiate into other cell types
-examples: photosynthetic, phloem, glandular cells, epidermal cells
-relatively inexpensive to build
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Collenchyma
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-form
cell membrane
primary cell wall: still cellulose, but unevenly thickened in some places
-function
provide flexible support but still allowing growth
elongating with stems and leaves they support
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Sclerenchyma
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-form
cell membrane
primary cell wall
secondary cell wall btwn primary and membrane, thickened and generally lignified (lignin restricts water transport)
-function
usually strengthened by lignin and rigid (can not elongate)
often dead at maturity
mechanical sclerenchyma: sclerids and fibers
conducting sclerenchyma: xylem tracheids + vessel elements
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tracheids
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thin
mm in length
tapered ends
water moves from cell to cell through pits
found in all vascular plants
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vessel elements |
wider and shorter than tracheids
make up longer (sometimes m in length) open "pipes"
dead at maturity
found in most flowering plants and few others
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Phloem |
vascular tissue for sugar solution transport
sieve cells and sieve tubes
accompanied by companion cells - nonconducting cells that are connected to the sieve-tube cells by plasmodesmata; in some plants they help load sugar in the sieve tube elements
live at maturity
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At functional maturity, why is xylem dead but phloem alive?
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xylem living tissue disintegrates leaving behind thickened cell walls as a nonliving transport system in which water moves laterally between pits
in phloem, pores facilitate the flow of fluid from cell to cell along sieve tube
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osmosis
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the diffusion of water across a membrane
in plant cells the well wall affects osmosis, the physical pressure of the cell wall pushes back against the parts of the cell (creates turgor)
water potential
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water potential |
a gradient in water potential is the driving force for water movement across cell membranes
increasing solutes in the water lowers solute potential
pressure increases pressure potential and tension decreases
water potential gradient = solute potential + pressure potential (units are MPa)
turgor - positive pressure potential
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3 Major pathways of water transport (soil to tissue)
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apoplastic ("non-living" space)
symplastic ("living" space)
transmembrane
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symplastic route of transport |
the cytosol of the cell is referred to as the symplast
water and solutes move continuum of cytosol withing plant tissue
minerals and water only cross the membrane ones and use plasmodesmata (narrow channels connecting cells) to move through
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apoplastic route of transport
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ions can diffuse across a tissue through the apoplast - the continuum formed by cell walls, extracellular spaces, and dead interiors of tracheids and vessels
one cross of the plasma membrane
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endodermis |
internal layer of cells in the root cortex surrounds the stele and functions as a last check point for the apoplastic route
minerals from symplast reach the the endodermis and continue through plasmodesmata of endodermal cells and pass in the stele
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casparian strip
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a belt made of suberin (impervious to water and minerals)
forces water and minerals moving through the apoplast to cross the plasma membrane of an endodermal cells and enter the stele via symplastic route
together the casparian strip and endodermis make sure not water and minerals reach the vascular tissue without crossing the plasma membrane
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Water, mineral, and sugar transport
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can occur by short-distance diffusion or active transport and by long distance bulk flow
diffusion is passive transport, uses aquaporins
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bulk flow |
driven by negative pressure - water enters through roots, and the xylem sap gets transported to leaves by bulk flow
pusing xylem up: root pressure; root cells pump minerals to lower water potential in stele; water flows from root cortex generating root pressure and pushing xylem sap
pulling xylem: the transpiration-cohesion-tension mechanism: transpirational pull - the loss of water vapor from leaf -> pulling force for upward movement, creating negative pressure
cohesion and adhesion facilitate long distance transport
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Why is the cohesion tension hypothesis the overall accepted hypothesis? |
for the most part xylem sap is not pushed from below, but pulled up by leaves using transpiration-cohesion-tension mechanism
water is constantly lost to transpiration, creating a negative pressure by surface tension, which creates a pull
cohesion makes water molecules stick together as they are pulled up
adhesion makes water stick to the cell surface as it is pulled up -> capillary action ensues
solar powered process- no energy expelled
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How do plants regulate how much water must be transported up?
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plants determine how much water needs to be transported up based on how much water has evaporated
plants regulate lose water through the stomata, which helps regulate the rate of transpiration
thick cuticles regulate water loss
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Phloem sap transported by positive pressure
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loading of sugar in sieve tube at the source lowers water potential inside the sieve tube and takes up water by osmosis
positive pressure forces sap to flow along the tube
pressure is relieved by phloem sap being unloaded at the sink (active or storage cells)
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How can water uptake be maximized by plants?
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more root surface area - root hairs
larger leaves maximizes surface area and evaporation, increasing the need and pressure for more uptake
less SA in leaves -> less water needed
some plants use fog as a leaf water source
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Why do deciduous trees drop their leaves during severe droughts?
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in order to reduce water loss from the leaves
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What structural adaptations allow cacti to live in the desert?
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smaller leaves to reduce transpiration
extremely thick cuticles to reduce water loss
some desert plants trap food in their leaves
stem photosynthesis
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How would phloem transport be different in summer vs early spring?
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phloem transport is increased in summer due to plants photosynthesizing and making sugar
in early spring it is not as hot so plants would need to produce less sugar
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For plants, meristems allow plants to grow or extend in...
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length
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What is the adaptive advantage of producing pairs of leaves on different sides of a stem?
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maximize light capture
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If the cutting takes off the bark (not just the periderm), what happens to the tree? Why?
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death
phloem layer that takes food to roots from leaves is removed, then roots die and no water is sent to leaves
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asexual reproduction
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produces exact copies of offsprings
single individual is the sole parent and passes copies of all its genes to the offspring
gives rise to clones
genetic differences come from mutations
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sexual reproduction
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2 parents give rise to the offspring
offspring vary genetically and have unique genome
2 gametes join to form zygote that is diploid
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animal reproduction
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diploid multicellular organism
meiosis produces haploid gametes (single cell)
fertilization produces a diploid zygote (single cell)
mitosis develops into organism (multicellular diploid)
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plants reproduction
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diploid multicellular organism (sporophyte)
meiosis produces haploid spores (single cell)
mitosis produces haploid multicellular organism (gametophyte)
fertilization produces 2n zygote (diploid single cell)
mitosis
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fungi reproduction
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2n zygote
meiosis splits into haploid cells (spores)
mitosis develops haploid unicellular or multicellular organism (hyphae)
organism produces gametes through mitosis
fertilization
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A life cycle with alternation of generations has:
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multicellular gametophyte and sporophyte forms
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For eukaryotes, alternation of generations is a shared derived trait for:
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land plants
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Sexual life cycles for animals, plants and fungi share which trait?
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union of gametes producing a 2n zygote
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Which type of plants display sporophyte dominance?
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all vascular plants
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Flower
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plant organ where reproduction occurs
Colorful petals used to attract insects for pollenation
stigma- sticky structure, receives pollen; part of carpal
style: structure that leads from stigma to ovary
carpal: female reproductive organs
ovary: becomes fruit; at base of carpal, contains ovules
ovule: found in the ovary and if fertilized it becomes a seed
anther: terminal sack of stamen where pollen is produced
stamen: male reproductive organs; filament and anther
pollen tube:delivers sperm to female gametophyte
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double fertilization
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2 sperms are discharged in the ovary, one fertilizes to make zygote and other combines with cell to make 3n endosperm tissue, a food source for the zygote (packaged in seed)
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fruit
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mature ovary of a flower
thickening of ovary around the seeds
protects seeds and aids in dispersal
disadvantage: takes a lot of energy to produce
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pollen and pollination
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pollen is male plant sperm
formed by the anther
in angiosperms, dispersed by wind, water, and animals
pollination is the transfer of pollen to the ovule in the ovary
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seeds
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plant embryo packaged with a food source
produced by fertilized ovary (ovule develops into seed)
disperse diploid sporophytes
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plant adaptations
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flowers attract pollinators, contain reproductive organs, located at highest point so wind disperses pollen
pollen dispersal and pollination: don't need water to disperse sperm (20% wind, 80% animals [~65% insects])
internal fertilization: embryo is safer, protected
seeds: protection of embryo and endosperm; can be dispersed long distances by various methods, higher chance of germination; dormant seeds survive harsh conditions
fruit: attract pollinators, aids in seed dispersal, long distance dispersal without water
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plant hormone
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organic compounds, either natural or synthetic, that modify or control one or more specific physiological processes within a plant
control plant growth and development
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seed dormancy
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trait evolved for seeds to remain dormant until mobilized by external trigger to make sure they germinate only in favorable conditions: enough light, temperature, and moisture for the seedlings to survive
ABA (absiciscic acid) keeps seeds dormant by lowering metabolic rate, suspending growth and development
water is often trigger, washes out ABA and seed starts to germinate
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Seed germination
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dormant seed triggered by water, water removes ABA and breaks dormancy
triggers release of Gibberllin (GA) which targets seed's outside wall
aleurone synthesizes and secretes alpha amylase - hydrolyzes nutrients in endosperm and breaks down starch to glucose
scutellum absorbs nutrients and sugars that are consumed by embryo as it grows into the seedling
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Gibberlin
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signals ovary to start thickening -> forms fruit, makes it grow larger by elongating the cells
gibberlin released during seed germination signals the aleuron to secrete the digestive enzyme and amylase that hydrolyzes the nutrients in the endosperm that will be used by the embryo while it is growing into a seedling
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Auxin
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phototrophism: as auxin moves down shoot it stimulates cell elongation
a plant stem exposed to light will have shaded and lit sides
shades side - more auxin the produce cell elongation
cells with auxin elongate while those cells on the lit side do not
causes stem to bend towards light
fruit formation: auxin is developing seed signals to ovary wall to start thickening resulting in the formation of the fruit
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Ethylene
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fruit ripeningL a burst of ethylene triggers ripening process
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