Unit 8: Plant Biology

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114 Terms

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Xylem

Tracheids and vessel elements that transport water and minerals from roots to leaves, in vascular bundles

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Transpiration

Loss of water vapour from stems/leaves, light energy turns water into vapour which exits through the stoma, a consequence of gas exchange in the leaf

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Transpiration stream

Movement of water from roots to leaves, created by transpirational pull, results from cohesion and adhesion

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Factors affecting transpiration

Heat ( +temp = +transpiration), Light (limits photosynthesis), wind (drying of atmosphere affects concentration gradient)

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water evaporates in _______ of the leaf

spongy parenchyma (when light energy transformed into heat energy)

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Transpiration pull

  • water diffusing out of stomata creates a negative pressure gradient

  • new water absorbed at roods creates a pressure differential (high in roots low in leaves)

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Gaurd cells function

guard cells become turgid or flaccid to open or close the stomata

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abscisic acid hormone

triggers potassium efflux from guard cells, lessens water pressure, traps water in leaf, released by dehydrated mesophyll cells

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ABA released by…

dehydrated mesophyll cells

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describe xylem cells

dead cells with no protoplasm, therefore, tube-like. Cell walls stiffened with lignin (necessary to withstand negative pressure; usually lower pressure in xylem than atmosphere) and thickened cellulose

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Pits

pores in xylem/vessel elements for water transfer between cells

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roots need a large surface area because…

they uptake water and minerals from the soil

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Fibrous roots

highly branched therefore large surface area for absorption

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Tap roots

one larger root with lateral roots, penetrates deep into the soil to access reservoirs

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Root hairs

small extensions on epidermis of roots, increase SA:V

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Describe diffusion of water into the root

water diffuses into the root hair by osmosis (follows the active transport of mineral ions from soil into root), across the cortex, then moves across the Casparian strip of the endodermis through plasmodesmata

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Casparian strip

in the endodermis, impermeable to the passive flow of water and ions

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Cuticle (leaf tissue)

Traps moisture inside leaf

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Epidermis (leaf tissue)

Provides protection for the leaf

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Palisade mesophyll

Tightly packed cells which increases SA, contains many chloroplasts, a major site of photosynthesis

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Spongy mesophyll

loosely packed tissue, water vapour binds to it, major site of gas exchange

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Vascular bundles

transport tissue containing xylem, phloem, and vascular cambium (undifferentiated)

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Stomata

Pores through which water, CO2 and O2 pass

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Monocots vs Dicots comparison

single cotyledon vs double cotyledon

long narrow leaf vs broad leaf

parallel veins vs network of veins

scattered vascular bundles vs ring of vascular bundles

floral parts x3s vs floral parts x4s or 5s

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Angiosperms vs Gymnosperms comparison

flower/fruit producing vs no flower/fruit

seeds encased in fruit vs unisexual naked seeds (cones) on leaf surface

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Meristem

undifferentiated plant tissue capable of indeterminate growth

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apical meristem

perform primary/apical growth at roots and shoot tip (can become new flowers and leaves)

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lateral meristem

perform secondary growth at cambium

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apical growth

primary growth at roots and shoots tips due to cell enlargement (mitosis) and cell division (cytokinesis)

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nodes

sections of apical growth in nodes

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inactive auxilary buds

formed from apical meristem in stems not used for nodes, creates new shoots, including leaves and flowers

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shoot apex

apical meristem and surrounding tissue

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lateral growth

increases width at cambium, most active in woody or shrub plants, growth rates are not constant

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vascular cambium

gives rise to secondary xylem and phloem

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cork cambium

contributes to bark

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auxins

hormones that promote apical growth (promote cell elongation, prevents growth in axillary bulbs) and tropic responses

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abscisic acid

promotes leaf death and stomatal closures

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hormone travel in plants

directly cell to cell or through phloem

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tropism

growth in response to directional stimuli

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auxins produced in…

apical meristem

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phototropism

growth in response to movement of light

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plant stem exhibits ______ phototropism while roots exhibit ______ phototropism

positive, negative

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auxin efflux pumps

  • membrane proteins that create concentration gradients of auxin in tissues by pumping auxin out of cell, into intracellular space, to diffuse into neighbour cell

  • can change location due to the fluidity of the cell membrane

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auxin influx

movement of auxin into a cell

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indoleacetic acid

the type of auxin involved in phototropism

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explain how auxin increases flexibility of shoot cell walls

  • auxins activate a proton pump (membrane protein) which pumps H+ ions into cell wall

  • lowers pH and breaks bonds in cellulose , loosens cell wall

  • auxins also upregulate expression of expansins which increase cell wall elasticity

  • an influx of H2O, stored in vacuole, can then increase cell size

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angiosperms

flowering plants, either monocots or dicots

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methods of asexual reproduction in plants

propogation

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methods of sexual reproduction in plants

spore formation, pollen transfer

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three phases of plant reproduction

pollination, fertilization, seed dispersal

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pollination

transfer of pollen grains from stamen to stigma

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mutualistic pollinators

  • a relationship in which both the pollinator and plant benefit

  • pollinators gain nutrients and facilitate plant reproduction

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cross-pollination

sexual reproduction between two plants, preferable to self-pollination to increase genetic diversity

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monoecious plants

capable of self-pollination, have both stamen and stigma

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flowers are colourful and fragrant to…

attract pollinators

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fertilization

  • nuclei of male gamete (in pollen grains) joins with nuclei of female gamete in ovule

  • pollen attaches to sticky stigma and forms a pollen tube to deliver sperm to egg in ovule

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Cotyledon

embryonic leaves capable of photosynthesis, stores nutrients, makes up the plant seed

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Testa

a strong and protective seed coat that usually must be broken for water intake before germination occurs.

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Epicotyl

aka plumule, embryonic shoot protected in the seed

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radicle

embryonic root protected in the seed

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Micropyle

small pore in the outer layer of the seed, allows for passage of water, also where pollen tube enters the seed

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the ovule develops a seed once it is ….

fertilised, sometimes develops a fruit around it

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seed dormancy period

a time of low metabolism and no growth/development, seed dehydrates to water content 10-15% total weight

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Germination

process by which a seed emerges from the dormancy period and begins to sprout

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essential conditions for germination

  • water - rehydrates plant tissues, triggers gibberellin

  • O2 - needed for resperation to create ATP

  • temperature - must be viable for enzyme activity

  • pH levels - must be viable for enzyme activity

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specialised conditions for germination

  • fire - must be exposed to intense heat

  • freezing - must experience and extreme cold period

  • washing - must be cleaned before germinating

  • digestion - to erode seed coat

  • scarification - seed coat weakened by physical damage

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flowering triggered by…

changes in gene expression

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Gibberellins

plant hormones that trigger stem elongation and germination of dormant seeds

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gene activation for flowering triggered by…

abiotic factors, linked to seasons when pollinators are most active, and day/night length

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Stamen composed of…

  • anther - pollen-producing organ

  • filament - stalk holding up anther so accessible to pollinators

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Pistil

female sex organ in plants

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Stamen

male sex organ in plant

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Pistil composed of…

  • stigma - sticky tip that catches pollen

  • style - elevates stigma and connects it to the ovule

  • ovule - contains female gametes, where seed develops

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Support structures/organs in plants

  • petals - attract pollinators

  • sepal - strong leaves that protect flower when in bud

  • peduncle - stalk

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photoperiodism

response of plant to lengths of light and darkness

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phytochromes

pigment in plants used to detect light and dark periods

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long-day plants

plants that flower around summer, require dark periods to be less than an uninterrupted critical night length to flower, because Pfr promotes flowering

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short-day plants

plants that flower in winter/fall, require dark periods to exceed an uninterrupted night length, because Pfr inhibits flowering

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Pr

the inactive form of phytochrome, this form is present when absorbing far red light (725 nm)

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Pfr

the active form of phytochrome, present when absorbing red light (660 nm)

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Pfr converted to Pr when it…

absorbs far red light or in sustained absence of light (darkness reversion)

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Pfr is most active during the day because…

there is an abundance of red light (660 nm) in sunlight

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Translocation

  • the movement of organic material in the phloem (sucrose, amino acids, hormones) from source to sink

  • Uses active transport

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Sugar is transported as ______ in plants because…

sucrose, soluble but metabolically inert

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Turgor pressure

water pressure in plant cells, water stored in vacuole

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Sieve tube cells

  • aka sieve tube members, long narrow cells connected to form a sieve tube

  • present in phloem

  • have few organelles and no nuclei to maximize space

  • have thick and rigid cell walls to withstand hydrostatic pressure

  • Have perforated end plates where cells fused, with holes

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sieve plate

connects sieve element cells together, porous to enable bidirectional flow, maintain pressure, and prevent congestion

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companion cells

  • present in phloem along with sieve tube members

  • provide metabolic support for sieve element cells and facilitate loading and unloading of materials at source and sink

  • possess an infolding plasma membrane, increase SA for material exchange

  • have many mitochondria to fuel active transport

  • have many transport membrane proteins to move materials

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plasmodesmata

small channels that connect the cytoplasms of sieve elements and companion cells and facilitate symplastic movement of materials

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Initial processes of seed germination

  • Water absorption

  • gibberellin is released which causes the production of amylase which hydrolyses starch → maltose → glucose

  • Glucose is used for cell resp.

  • Glucose can be converted into cellulose to produce cell walls

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Effects of light on transpiration

speeds up transpiration bo warming the leaf and opening stomata

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Effects of humidity on transpiration

decreased humidity increases transpiration bc concentration gradient of water in air vs leaf

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Effects of wind on transpiration

increases transpiration by moving humid air away from the leaf

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Effects of temperature on transpiration

high temperatures increase transpiration because more water evaporates

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Effects of soil water on transpiration

if water intake at roots is slow, turgor loss occurs and stomata close, decreasing rate of transpiration

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Effects of CO2 on transpiration

high CO2 levels in the air around the plant often cause the guard cells to lose turgor and the stomata close.

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Vessel elements

dead cells with no cytoplasm, cellulose walls reinforced by lignin

only present in angiosperms, tracheids are present in all vascular plants

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tracheids

tapered cells, exchange H2O by pits only, cellulose walls with lignin

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Negative pressure gradient in xylem

  • water is pulled from the xylem under tension (low pressure)

  • due to the adhesive attraction between H2O and leaf cell walls

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Adaptations of xerophytes

  • CAM physiology; stoma open at night, closed in the day, reducing loss of H2O by evaporation

  • reduced and rolled leaves, lower SA for evaporation and less exposure of stomata to air

  • thick cuticle to prevent water loss

  • low growth - shaded and less wind