Definition of a Plant: A multicellular, eukaryotic,
photosynthetic autotroph. The cell walls contain cellulose and they
store excess glucose as starch. They also exhibit alternation of
generations one will be dominant over the other. The sporophyte
generation is 2n (diploid) and the gametophyte generation is n
(haploid).
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Evolution of Plants Plants evolved from aquatic green algae
about 500 mya. Paleozoic era Adaptations to dry land Most plants
are land plants today
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Two Groups of Plants Non-vascular Bryophytes no xylem or phloem
Vascular Tracheophytes contain xylem and phloem conducting tissue
Xylem conducts water Phloem conducts dissolved sugars
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Primary Functions of Plants Absorb carbon dioxide Release
Oxygen Hold soil in place Provide for the transfer of energy from
the sun to other organisms AKA Food Provides habitats for
animals
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Division - Bryophyta Non-vascular Mosses, horn-worts,
liverworts They lack any lignin-fortified tissue so they cant grow
very tall. The gametophyte generation is dominant in bryophytes (it
is the green part that you see and the sporophyte is the stalk
coming out of the gametophyte.)
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Bryophyte continued Female gametophyte has an Archegonium that
produces the egg (n) Male gametophyte has Antheridia that produces
sperm (n)- These are motile sperm and must have water in order to
fertilize the egg. Fertilization occurs within the archegonium and
produces the zygote. The Sporophyte then grows from the zygote out
of the gametophyte and produces sporangia that produce spores.
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What do Bryophytes do? Stabilize and form soil from rocks are
pioneers in primary succession and are necessary to form the soil.
Used as fuel (peat moss) Retains moisture when mixed with soil
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Tracheophytes are: Vascular plants Xylem and Phloem used for
transport of water and sugars Xylem and Phloem contain lignin that
gives the plant support so that it can stand up against gravity
Roots absorb water and prevent desiccation (drying out), and anchor
in the soil giving extra support Leaves increase the photosynthetic
area Sporophyte is the dominant generation
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Two Groups of Tracheophytes Seedless Plants Ferns Pteridophytes
Homosporous They produce only one type of spore Stay fairly small
because they must have water to reproduce due to the fact that
sperm are flagellated and swim to get to the archegonium to
fertilize the egg. Ancient Ferns were tree size They reabsorbed so
much carbon dioxide during the Carboniferous period that the Earth
experienced Global Cooling Most turned into Coal that is now one of
the causes of Global Warming
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Life Cycle of a Fern
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Seed Plants Heterosporous Produce megaspores female gametophyte
and microspores male gametophyte Male gametophyte does not have
flagella so they dont need water Gymnosperms Cone bearing naked
seed (conifers pine, firs, redwoods, junipers, and sequoia)
long-lived organisms
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Gymnosperms First seed plants to appear Seeds are not enclosed
in a fruit Replaced the ferns because they were better adapted for
land Have needle shaped leaves with a waxy covering that helps to
prevent drying Use the wind for pollination
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Angiosperms Flowering plants seeds are enclosed in a fruit Most
diverse and abundant of all plant species Color and scent of
flowers attracts animals for pollination and dispersal of seeds
Ovary becomes the fruit (fruit is ripened ovary) Ovule becomes the
seed
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Seed/Fruit adaptations Maples have wings so that the wind can
carry them Fruit has burrs that stick to animal fur Brightly
colored and sweet so that animals eat them and then poop the seeds
with fertilizer so it grows rapidly Some float on water (coconut)
Fruit prevents drying out of seeds and protects them until they are
ready to be dispersed.
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Two types of Angiosperms Monocots have one cotyledon (seed
leaf) Scattered vascular bundles Parallel veins in the leaves
Flower parts in 3s Fibrous roots
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Dicots have two cotyledons (seed leaves) Vascular bundle is
arranged in a ring Veins are netlike or branched Flower parts are
in 4s or 5s Have taproots
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Plants: Part II How plants Grow Plants can only grow from
meristematic tissue (meristem) it is embryonic tissue (stem cell)
Located at the tip of the roots and in the buds of shoots is apical
meristem. The plants roots grow down into the soil from this tissue
and grow taller from the top of the plant.
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Primary Growth Zone of cell division apical meristem: actively
dividing cells Zone of elongation Cells are not dividing but are
getting longer and push the root cap down deeper into the soil Zone
of differentiation: Cells become specialized into three tissue
systems A. The protderm becomes the epidermis B. The ground
meristem becomes the cortex for storage C. The procambium becomes
the primary xylem and phloem.
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Vascular Cambium is what makes woody plants thicker.
Responsible for secondary growth.
Dermal Tissue 1. Covers and protects the plant. Endodermis
Epidermis Modified cells like guard cells, root hairs, and cells
that make waxy cuticle
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Vascular Tissue Xylem conducts water and dissolved minerals
(cells are dead at maturity) Consists of tracheids and vessel
elements Both types of cells are dead at maturity Tracheids long
thin cells that overlap and are tapered at the ends. Water passes
from one cell to another through pits. Cells walls are hardened
with lignin. Xylem is what makes up wood.
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Tracheid
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Vessel Elements wider than tracheids, but also shorter than
tracheids. Aligned end to end and the ends are perforated to allow
free flow through the vessel tubes. Seedless vascular plants and
gymnosperms have only tracheids. Seed plants have both tracheids
and vessel elements.
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Comparison of Tracheid and Vessel Element
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Phloem Carries sugars from the leaves to the rest of the plant
by active transport. Made of sieve tube members (elements) with
sieve plates at the end to connect them. These cells are alive at
maturity but lack a nucleus, ribosomes and vacuoles. Companion
cells are connected to each sieve tube member and provides the
sieve tube cells with what they need.
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Ground Tissue Most common type of tissue in a plant Functions
in 1)support 2) storage 3) photosynthesis Three types of ground
tissue Parenchyma Sclerenchyma Collenchyma
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Parenchymal Cells They are like a regular plant cell but they
lack secondary cell walls Are totipotent Many contain chloroplast
and carry out photosynthesis mesophyll cells in the leaf
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Collenchymal Cells Unevenly thickened primary cell walls and
lack secondary cell walls and lignin to harden them They are alive
at maturity and function in support of the growing stem. They are
the strings in celery
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Sclerenchymal Cells Have thick primary and secondary cell walls
Function in support Two types: 1) fibers 2) sclerids Fibers in
bundles and are used in making rope Sclerids short and irregular
and make up the rough seed coat and pits. They give fruit the
gritty texture like in pears.
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Roots and their Function 1) absorb water and nutrients 2)
anchor the plant in the soil 3) store food
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Dicot Root
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Parts of the Root and their Fuctions Epidermis- covers and
protects, absorbs Root hairs increase surface area Cortex Storage
of starch and sugar Stele consists of vascular tissue and is
surrounded by the pericycle (contains meristematic tissue) Lateral
roots arise from the stele Endoderm Surrounds the vascular
cylinder
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Casparian strip a band of cell wall containing suberin and
lignin, found in the endodermis. It restricts the movement of water
across the endodermis. Suberin a waxy like substance that surrounds
the casparian strip and acts as a barrier to water and solute
movement across the casparian strip.
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Types of Roots 1) Drop Type of aerial 2) taproot 3) fibrous 4)
Adventitious roots 5) Prop 6) Aerial pneumatophores - snorkel
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The Leaf
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Parts of the leaf Cuticle covered with cutin (a wax) to prevent
water loss Guard Cells modified epidermal cells that surround the
stomata and help to control the opening and closing of the
stomates. They do contain chloroplast. Stomata Openings on the
underside of the leaf where gases, CO2 is taken in, O2 is released
and water vapor is lost by transpiration. 90% of water escapes
through the stomates
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Pallisade and spongy mesophyll pallisade is underneath the
epidermis and the spongy is in the middle of the leaf. The primary
function is photosynthesis. Vascular bundles veins located in the
mesophyll and carry water and nutrients from the soil to the leaves
and carry sugars from the leaves to the rest of the plant.
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Control of Stomata by Guard Cells In the light, guard cells
actively pump protons out, and this increases the uptake of
potassium and chloride ions. (No light, potassium and chloride
diffuse out of guard cells) Higher concentrations of potassium and
chloride gives guard cells a negative water potential. This causes
water to flow into the cells and increases the turgor pressure.
Increased turgor pressure stretches the cells and opens the stoma.
(Decreased turgor pressure (flacid), the stomata closes. Basically,
the cellulose fibers are arranged radially so that when the cells
absorb water they curve outward and open the stomata. They curve
inward when flacid and close the stomata.
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What will make the guard cells open? Decreased carbon dioxide
stimulates stomata to open. Happens when photosynthesis begins.
Increase in potassium ions in the guard cells which lowers the
water potential Stimulation of the blue light receptor Active
transport of H+ out of the guard cells
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What will make stomates close? 1. Lack of water 2. High
temperatures stimulates cellular respiration and increases carbon
dioxide 3. Abscisic acid produced by mesophyll cells in response to
dehydration and guard cells close the stomata
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Transport of Water in Plants through the Xylem Water rises in
the xylem against gravity. 2 forces accomplish this: 1) Root
Pressure 2) Transpirational Pull
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Transpirational Pull Transpiration is the evaporation of water
through the stomates in the leaves. Causes negative pressure as the
water leaves. This negative pressure is also called tension. Water
molecules cling to each other due to hydrogen bonding. This is
called cohesion and to the walls of the xylem which is called
adhesion.
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Transpirational pull-cohesion theory The negative pressure
created when water evaporates pulls other water molecules up the
xylem. This is because the water molecules are clinging to each
other. 1)Water diffuses out of the stomata by evaporation. This is
called transpiration. 2)Water evaporates from mesophyll cell walls
3)Tension pulls water from the veins into the apoplast surrounding
the mesophyll cells 4) This pulls water in the veins of the leaves
upward and outward 5)This pulls the water in the xylem of the shoot
and root upward 6)Cohesion between water molecules forms a
continuous column of water from the roots to the leaves 7)Water
enters the root and moves into the xylem by osmosis
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Apoplast and Symplast: The movement of water across a plant is
called lateral movement and it occurs along symplast and apoplast.
The symplast is a continuous system of interconnected cells via
plasmodesmata. The apoplast is the network of cell walls and
intercellular spaces within a plant body that allows extracellular
movement of water within a plant.
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When it gets to the endodermis it can continue to the xylem
through the symplast, but water in the apoplast must pass across
the endodermis by diffusion.
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Translocation The movement of carbohydrates and other solutes
through the plant in the phloem. Moves from sources to sinks. A
source is an organ that produces by photosynthesis sugars A sink is
an organ that uses sugars such as a flower, fruit, etc.
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Active transport of sugars
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Sources and Sinks can change roles. If photosynthesis is not
occurring then sugars can be released from the roots or stems to
the leaves for use in cellular respiration.
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Plant Reproduction Asexual vegetative propagation Stem Leaf
Root Produces an entirely new plant that is a clone Used in
grafting, cuttings, runners
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Sexual Reproduction 1. Pollination Pollen grain contains 3
monoploid nuclei, one tube nucleus and 2 sperm nuclei Lands on
stigma Pollen absorbs moisture and sprouts a pollen tube that goes
down the style 2 sperm nuclei travel down the tube to the ovary One
sperm fertilizes the egg and becomes the embryo
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Fertilization continued The other sperm fertilizes the two
polar bodies and becomes the triploid (3n) endosperm. This is
called double fertilization The endosperm becomes the food for the
developing embryo The ovule becomes the seed In dicots the food in
the endosperm is transported to the cotyledons In monocots the
endosperm is liquid
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The seed Seed coat protective outer layer Embryo hypocotyl,
epicoltyl, and radicle Radicle becomes the root Hypocotyl becomes
the lower stem and the epicotyl becomes the upper stem
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Seed Germination
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Steps in Germination 1) Seed coat imbibes water, swells and
ruptures 2) Radicle emerges 3) epicotyl elongates 4) radicle grows
down 5) epicotyl pulls plumule out from between the cotyledons
6)pulls plumule (first bud) backwards through the soil so leaves
arent damaged 7) epicotyl straightens and leaves open out
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Plant Hormones Coordinate growth, development, and response to
environmental stimuli Auxins 1) Auxin IAA Indoleacetic acid 2)
responsible for phototropism 3)Enhances apical dominance the
preferrential growth upward rather than outward (terminal bud
suppresses the lateral buds) 4) stimulates stem elongation and
growth by softening the cell wall
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First hormone discovered Synthetic Auxin is roundup a weed
killer Can also be used as a rooting powder Sprayed on tomatoes
causes fruit production without pollination produces seedless
tomatoes
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Cytokinins Stimulates cytokinesis and cell division Works with
auxins to promote growth Works against auxins in relation to apical
dominance Delays senescence (aging) by inhibiting protein breakdown
Produced in roots and travel upward in the plant
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Gibberellins Promotes stem and leaf elongation Works with
auxins to promote growth Induces bolting or rapid growth of
stalk
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Abscisic Acid 1) inhibits growth 2) Enables plants to withstand
drought 3)closes stomata during water stress 4) works in opposition
to growth promoting substances 5)Promotes seed dormancy
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Ethylene Gas 1)Promotes fruit ripening Positive feedback 2) Is
produced in times of stress in large amounts 3) promotes apoptastic
programmed cell death cell reuses chemicals from the breakdown of
cell parts to survive during stress ( drought, flood, injury,
infection)
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Promotes leaf abscission leaf falling off A scar forms where
the leaf falls off and prevents and prevents pathogens from
entering. This is due to an increase in ethylene and a decrease in
auxin. Ethylene works in opposition to auxin.
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Tropisms The growth of a plant towards or away from a stimulus
Phototropism towards light Thigmotropism towards touch
Geo/gravitropism towards or away from gravity Positive tropism
towards the stimulus Negative tropism away from the stimulus
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Phototropism due to unequal distriubution of auxins which
accumulate on the side of the plant away from the light. This side
grows longer while the top side doesnt grow, causing it to bend
toward the light. Geotropisms occur due to interaction of auxins
with statoliths which are specialized plastids with dense starch
granules.
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Signal Transduction Pathway 1) Reception 2) Transduction 3)
Response A receptor is stimulated which undergoes a conformation
change and is known as a ligand This activates a second messenger
(cyclic AMP, or cyclic GMP) and this messenger goes to the nucleus
where transcription occurs. The gene is then translated into a
response for the plant.
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Adaptations to Land 1) Cell walls support 2) Roots and root
hairs absorption of water and nutrients 3) Stomates gas exchange 4)
Waxy Cuticle 5) Gametangia prevents drying of zygote 6)
Sporopollenin a tough polymer that is resistant to environmental
damage and protects the plants in a harsh terrestrial environment
and is found in the walls of spores and pollen 7) Seeds and Pollen
protective coat that prevents drying and are how offspring are
dispersed. 8) Reduced gametophyte generation 9) xylem and phloem
10) Lignin for support