Transcript PLANT DIVERSITY II

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 Get onto land, plants had to evolve
a way to keep from drying out and
stand upright.
 Have to be able to transport
nutrients, water over long short
distances.
 Plant structures divided into 2
systems: root system (below
ground), shoot system (above
ground).
 Systems rely on one another; roots
require shoots to photosynthesize.
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 Water and mineral salts from soil
enter plant through epidermis
(outer layer) of roots, cross root
cortex, pass into stele (where
xylem is), flow up xylem vessels to
shoot system.
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Fig. 36.7
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
 Most absorption of water and
minerals occurs near root tips,
epidermis is permeable to water and
root hairs are located.
 Root hairs allow for maximum uptake.
 Most plants form partnerships with
symbiotic fungi for absorbing water
and minerals from soil.
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 Water and minerals in root cortex
cannot be transported to rest of
plant until they enter xylem in
stele.
 Endodermis surrounds stele and is
last checkpoint for absorption into
vascular tissue.
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 Some plants have adventitious
roots that arise aboveground from
stems or even from leaves.
 Seen in corn - help keep plant
upright.
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 1Stems have nodes (leaves attached)
internodes (spaces between nodes)
 Where leaves meet stems are axillary
buds - vegetative branch could form.
 Terminal bud - growth of young shoot
is concentrated - growth happens
vertically (apical dominance)
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Modified shoots
 1Stolons - “runners” of strawberry
plants - grow on surface so parent
plant can asexually reproduce in
large numbers.
 2Rhizomes – ginger - horizontal
stems that grow underground.
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Rhizomes
 3Tubers – potatoes - swollen ends
of rhizomes specialized for food
storage.
 4Bulbs – onions - vertical,
underground shoots consisting
mostly of swollen bases of leaves
that store food.
Tubers
Bulbs
 2Leaves consist of a flattened
blade and a petiole (stalk)
 Some leaves have evolved other
purposes - spines of cacti for
defense, leaves modified for water
storage, brightly colored leaves
that attract pollinators.
 3Flowers – discussed later
 Each organ has 3 tissues: dermal,
vascular, and ground.
 Dermal tissue - epidermis (covers
and protects)
 Epidermis of leaves and most stems
secretes waxy coating, cuticle, that
helps parts of plant retain water.
 Land plants - true roots, stems,
leaves.
 Xylem carry water, minerals up from
roots - dead at maturity.
 Phloem - living tissue - distribute
sugars, amino acids, other organic
products.
http://www.bbc.co.uk/schools/gcsebitesize/img/bixylemphloem.gif
 2 types of xylem cells: vessel
elements, tracheids.
 Both dead at maturity - help thicken
walls to promote water flow.
 1Tracheids - long, thin cells with
tapered ends.
 2Vessel elements - wider, shorter,
thinner walled, less tapered than
tracheids.
 2 types of phloem cells - companion
cells and sieve tube members.
 1Sieve tube members - tubes that
material moves through.
 2Companion cells assist sieve tube
members.
 Xylem sap flows into veins of leaf
providing them with water.
 Plants lose water through
transpiration (water is replaced
through water transport)
 Xylem sap must rise against gravity
through pumping system.
 Accumulation of minerals in stele
lowers water potential, generating
positive pressure (root pressure) forces fluid up xylem.
 Plants rely on osmosis.
 Direction of water movement depends
on solute concentration and physical
pressure (water potential)
 Water moves from high water
potential to low water potential.
 Water potential is measured in MPa,
abbreviated psi.
 Pressure to water can reverse
movement of water would normally
move.
 Using syringe (negative pressure) can
force water to move upwards.
 Combined effects of pressure and
solute concentrations on water
potential: psi = psiP + psis
 psiP - pressure potential psis - solute
potential (or osmotic potential).
 Flaccid cell, psip = 0.
 If placed in solution with lower psi,
water will leave cell - will
plasmolyze, by shrinking and pulling
away from wall.
 As cell begins to swell pushes
against wall (turgor pressure)
 Placed in pure water - cell will have
lower water potential due to
solutes; water will enter cell.
 Become turgid (firm)
 Simple diffusion is not efficient
enough.
 Water and solutes move through
xylem vessels and sieve tubes by
bulk flow - movement of fluid
driven by pressure.
 Tension allows for transport of
materials.
 Transpiration forces water to move
up plant in stream (negative
pressure) - allows materials to move
in bulk.
 Larger diameter of stem = faster
material can move.
 Other items regulate water flow.
 1Aquaporins - specific transport
proteins that aid in passive
movement of water.
 2Tonoplast (membrane that bounds
vacuole), regulates molecular traffic
between cytosol and contents of vacuole
(cell sap)
 3Plasmodesmata (connections between
cells) connect symplast (cytoplasm
stream)
 Cell walls of adjacent plant cells apoplast.
 Leaf epidermis composed of cells tightly
locked together.
 Full of stomata - openings that allow
diffusion of carbon dioxide, water vapor,
and oxygen between leaf and air.
 Size of stomata controlled by guard cells open and close opening using turgor
pressure.
 Guard cells open during day to allow
CO2 for photosynthesis; close at night
to limit loss of water vapor through
transpiration (evaporation of water
from leaves)
 Decreased turgor pressure causes
guard cells to close (need to conserve
water)
 Absorption of sunlight drives
transpiration by causing water to
evaporate from mesophyll cells and
by maintaining high humidity in air
spaces in a leaf.
 Sunlight drives transport of water.
 Root pressure causes guttation
(oozing of water droplets in
morning on tips of grass blades)
 Roots accumulate water during
night, transpiration is low, so water
enters leaf at faster rate.
 Xylem sap pulled through plant
creating stream of water that cannot
be broken.
 Cavitation (formation of water vapor
pockets in xylem vessel) breaks chain.
 Occurs when xylem sap freezes in
water.
 Cannot be fixed in trees, but stream
can form around it.
 When transpiration exceeds delivery of
water by xylem, (soil begins to dry out)
leaves wilt as cells lose turgor pressure.
 Guard cells control diameter of stomata
by changing shape, widening or
narrowing gap between the 2 cells.
 Potassium helps in regulation of
guard cells.
 Their opening is regulated in 3
ways.
 1Blue-red wavelengths signal plant
to start photosynthesizing.
 2Depletion of CO2.
 3Internal clock in plant cues plant to
start photosynthesizing - started at
dawn.
 Opening and closing cycle of stomata is
circadian rhythm, cycles that have
intervals of approximately 24 hours.
 Plants adapted to arid climates
(xerophytes) have leaf modifications
that reduce rate of transpiration.
 Some - smaller, thicker leaves.
 Some shed leaves during extremely
dry months.
 Some - stomata concentrated on
lower (shady) leaf surface.
Phloem sap
 Phloem transports organic products
of photosynthesis throughout plant
via translocation.
 Phloem sap - aqueous solution sugar, mostly sucrose - is most
abundant solute.
 Xylem - unidirectional movement;
phloem movement variable.
 Sieve tubes carry food from sugar
source to sugar sink.
 Sugar source - plant organ (especially
mature leaves) where sugar is being
produced by photosynthesis or
breakdown of starch.
 Sugar sink - organ (growing roots, shoots,
or fruit) that is net consumer or storer of
sugar.
 Storage organ (like a tuber) can be sink in
summer (storing for winter) but source
during in beginning of spring
 http://www.pearsoned.ca/school/science11/biology1
1/sugartransport.html
 Neither dermal tissue nor vascular
tissue.
 In dicot stems, ground tissue
divided into pith, internal to
vascular tissue, and cortex,
external to the vascular tissue.
 3 different types of plant cells:
parenchyma, collenchyma, and
sclerenchyma.
 1Parenchyma cells have walls that
are thin and flexible; typical plant
cells (sieve-tube members)
 2Collenchyma cells - thicker walls
than parenchyma cells.
 Used for support in growing plants.
 3Sclerenchyma cells function as
supporting elements of plant.
 Annual plants complete life cycle in
single year or less.
 Biennial plants - two years.
 Plants that live many years, including
trees, shrubs, and some grasses, are
perennials.
 Growth in plants due to embryonic
(undifferentiated) cells meristems.
 Can undergo cell division to produce
new organs through life of plant.
 Elongate and differentiate into cell
types depending on tissue of plant.
 Apical meristems found at tips of
roots and stems.
 Allow for growth in length – only
happens at tips of roots and stems.
 Primary growth – lengthwise,
secondary growth - widthwise.
 Lateral meristems - secondary
growth.
 Root tip protected by root cap to
protect meristem.
Lateral meristems
 2 cambiums responsible for secondary
growth.
 1Vascular cambium - meristem to
produce secondary xylem and secondary
phloem.
 2Cork cambium - meristem for tough,
thick covering for stems and roots replaces epidermis.
 As secondary growth continues
over years, layer upon layer of
secondary xylem accumulates,
producing wood - actually dead
cells.
 Growth in areas like Maine occur in
cycles through dormancy then
growth which produce growth rings.
 Bark - all tissues external to vascular
cambium (secondary phloem, cork
cambium, and cork)
 2 types of secondary phloem:
heartwood and sapwood.
 Heartwood (hardwood) no longer
conducts water (responsible for
strength in old trees) while sapwood
(softwood) functions in transport of
water and minerals.
 4 groups of land plants: bryophytes,
pteridophytes, gymnosperms, and
angiosperms.
 Bryophytes - mosses.
 Pteridophytes - ferns.
 Gymnosperms – pines, conifers.
 Angiosperms - flowering plants.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
 Bryophytes - offspring remain
attached to parent plant.
 Non-vascular plants.
 Vascular plants - vascular tissues,
cells join into tubes that transport
water, nutrients throughout plant
body.
http://www.science.siu.edu/landplants/Bryophyta/images/Physcomitrium.JPEG
 Ferns - seedless plants.
 Seed - plant embryo packaged along with
food supply within protective coat.
 Early seed plants gave rise to diversity
of present-day gymnosperms, including
conifers.
 Modern plants angiosperms.
http://www.rockhillridge.com/images/hayes/Ferns,%20Hayes%20Tract%206%2003-web.jpg
Fern
 Plant evolution:
 1Origin of bryophytes from algal
ancestors.
 2Origin, diversification of vascular
plants.
 3Origin of seeds.
 4Evolution of flowers.
 Plants – multicellular, derive energy and
nutrition through photosynthesis.
 Plant cell walls - cellulose.
 Different from algae - apical meristems,
alternation of generations, sporangia
that produce walled spores.
http://www.botany.hawaii.edu/faculty/webb/BOT311/bot311-00/PlantCellWalls00/CellWallHemiLab.jpg
 Plants need to grow to maximize
absorption.
 Done through apical meristems undifferentiated cells that divide
when needed.
 Located at tips of roots, shoots.
 Multicellular plant embryos develop
from zygotes - stay in tissues of
female parent.
 Land plants - embryophytes.
 Parent provides nutrients to
embryo.
 Alternation of generations -
gametophyte produces haploid
gametes through mitosis that get
fertilized (by other gametes); form
a diploid zygote that will grow into
mature sporophyte.
http://fig.cox.miami.edu/~cmallery/150/mitosis/sf9x7c.jpg
 Sporophyte produces haploid
single-celled spores - reproductive
cells - grow into gametophyte by
mitosis.
 Size of sporophyte and
gametophyte differ in plant
species.
 Bryophytes - gametophyte
dominant generation.
 Pteridophytes, gymnosperms, and
angiosperms - sporophyte dominant
generation.
http://www.sbs.auckland.ac.nz/info/schools/nzplants/images/moss/moss_major_parts1.jpg
 Spores - covered by sporopollenin –
resistant to outside stress.
 Sporangia found on sporophyte produce spores.
Sporopollenin
 Female gametangium (gamete
producing organ) – archegonium produces single egg cell in vase shaped organ.
 Male gametangia – antheridia produce many sperm cells released to
environment.
 Sperm fuses with egg in archegonium.
Female
Fusion of sperm and egg
 Land plants have cuticle – protects
from drying out, microbes.
 Stomata allow exchange of carbon
dioxide and oxygen between outside
and interior.
 Plants also produce secondary
compounds - alkaloids, tannins, and
phenolics such as flavonoids bitter tastes, strong odors, or
toxic effects (protection for plant)
 Some used for medicinal purposes.
http://www.naturalproductsmarketplace.com/articles/i461a12.jpg
Origin of land plants
 Chloroplasts of land plants most
similar to plastids of green algae.
 In both - cellulose comprises 2026% of cell wall.
http://www.rsbs.anu.edu.au/profiles/Brian_Gunning/Web%20PCB/Ch%2010%20Plastids/Topic%2005%20Chloroplasts-Charophyceae/10%2005%2010.jpg
Bryophytes
 3 phyla - 1phylum Hepatophyta –
liverworts, 2phylum Anthocerophyta
– hornworts, 3phylum Bryophyta –
mosses.
 Gametophytes dominant phase of
life cycle.
 Bryophytes anchored by tubular
cells or filaments of cells rhizoids.
 No conducting tissues (xylem,
phloem) to distribute water and
organic compounds within
gametophyte – so very small.
http://userwww.sfsu.edu/~biol240/labs/lab_10plantoverview/media/rhizoids.jpg
 Most mosses lack cuticle, only 1 cell
thick – quick absorption from
surroundings.
 Gametophytes produce gametes in
gametangia.
http://io.uwinnipeg.ca/~simmons/Chap29a98/img016.jpg
Bryophyte Reproduction
 Sperm swim toward archegonia,
drawn by chemical attractants.
 Zygotes and young sporophytes
retained and nourished by parent
gametophyte.
 Moss sporophytes have foot, elongated
stalk (seta), and sporangium (capsule).
 Foot gathers nutrients and water from
parent gametophyte via transfer cells.
 Stalk conducts materials to capsule.
 Capsule – disperse spores.
 Common in wetlands, wind dispersal
allows for inhabiting many different
areas.
 Some moss form deposits of undecayed
organic material – peat.
 Forms peat bogs.
Pteridophytes
 Vascular plants have food transport
tissues (phloem) and water
conducting tissues (xylem) with
lignified cells.
 1st vascular plants, pteridophytes,
were seedless.
http://www.florelaurentienne.com/flore/Groupes/Pteridophytes/images/Adiantum_pedatum_940528_21_800.jpg
Seedless Vascular Plants
 Cooksonia (extinct) - earliest known
vascular plant (400 MYA)
 2 modern phyla:
 1Phylum Lycophyta – lycophytes.
 2Phylum Pterophyta -- ferns, whisk
ferns, and horsetails.
Cooksonia
 Lycophytes - small leaves
(microphylls) with single
unbranched vein.
 Leaves of other vascular plants,
megaphylls much larger and highlybranched.
Reproduction in
Pteridophytes
 Homosporous (one sex) sporophyte
produces a single type of spore.
 Heterosporous sporophyte (two sexes)
produces 2 kinds of spores.
 Megaspores - females gametophytes.
 Microspores - male gametophytes.
Heterosporous
Fig. 29.23
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
 Modern lycophytes - tropical
species that grow on trees as
epiphytes, using trees as
substrates, not as hosts.
 Specialized leaves (sporophylls)
bear sporangia clustered to form
club-shaped cones.
http://www.tcr.gov.nl.ca/nfmuseum/images/osmundaclaytoniana3barrdharbourhilljuly122002.jpg
 Phylum Pterophyta – ferns and
relatives.
 1Psilophytes - whisk ferns.
 2Sphenophytes – horsetails - found in
marshy habitats, along
streams and sandy roadways.
 3Ferns - leaves (fronds) may be
divided into many leaflets.
 Produce clusters of sporangia (sori)
on back of green leaves
(sporophylls) or on special, nongreen leaves.
 Dispersed by wind.
Sporophylls
Sori
 Seed plants - vascular plants that
produce seeds.
 3 adaptations that seed plants
have:
 1Gametophyte more reduced.
 2Seed evolved.
 3Pollen evolved.
 Gametophytes of seed plants
almost invisible.
 Gametophytes still exist - plants
can destroy themselves at this
stage if there something wrong
with plant.
 Seed - sporophyte embryo packaged
with food supply within protective
coat.
 Seed plants - 2 different types of
sporangia – each produces different
spores: megaspores (grows into
female gametophyte) and
microspores.
 Gametophytes stay in sporophyte as
it develops.
 Ovule contains integuments
(protective covering), megaspore, and
megasporangium.
 Female gametophyte develops inside
megaspore; produces 1 + egg cells.
 Fertilized egg develops into embryo.
 Whole ovule develops into seed
 Microspores (pollen) – light, carried
through air.
 Pollen will create pollen tube - allow
sperm to travel down into female
gametophyte.
 2 groups of seed plants:
gymnosperms and angiosperms.
Gymnosperms
 4 phyla of gymnosperms still
around.
 1Phylum Ginkgophyta - Ginkgo
biloba.
 2Phylum Cycadophyta - cycads -
look like palm trees.
 3Phylum Gnetophyta – 3 different
types of plants including ephedra.
Cycad
Ephedra
 Phylum Coniferophyta - largest phyla -
includes conifers.
 Conifer because of reproductive
structure (cone)
Conifers
 Conifers - evergreen - keep leaves all
year long.
 Needles help in dry conditions.
 Conifers - pines, firs, spruces, larches,
yews, junipers, cedars, cypresses, and
redwoods.
Life cycle of gymnosperms
 Conifers - heterosporous (separate male
and female gametophytes)
 Produce both pollen cones and ovule
cones.
 During pollination, pollen falls on ovule.
 Pollen creates pollen tube - digests
through megaspore.
 Fertilized megaspore goes through
meiosis to produce 4 haploid cells.
 1 cell will turn into female gametophyte;
other 2 or 3 cells (archegonia) will
develop within gametophyte.
Angiosperms
 Angiosperms - flowering plants -
produce flowers and fruit.
 Phylum Anthophyta divided into two
groups: monocots and dicots.
 Most monocots - leaves with parallel
veins, dicots - netlike venation.
 Monocots (grasses) usually have
fibrous root systems - look like
mat.
 Dicots (flowers) have taproot
system - one large root.
 Vascular tissue runs length of stem
in vascular bundles.
 Dicots - vascular bundles arranged
in a ring; monocots - scattered.
 Angiosperms - long tracheids that help
to transport water and to support plant.
 Flower specialized for reproduction.
 Most angiosperms rely on pollination
through animals; grasses rely on random
chance.
 Flower - specialized shoot - 4 circles of
modified leaves: sepals, petals, stamens,
and carpals.
 1Sepals - base of flower - modified
leaves that enclose flower before it
opens.
 2Petals lie inside ring of sepals - usually
colorful in animal pollinated plants.
 3Stamen – male organ - thin, stalk-like
filament with sac at top (anther)
 Anther produces haploid spores that
develop into pollen grains.
 4Carpal – female organ - contains three
parts: stigma, style, ovary.
 Stigma - sticky top part of flower -
extends beyond flower, catches pollen.
 Style connects stigma to ovary at base of
pistil - allows sperm to reach ovules.
 Ovary - enlarged area at base of pistil that
contains one or more ovules.
 The entire structure is the carpal.
 An ovule contains the egg nucleus.
 Fruit - mature ovary.
 As seeds develop from ovules after
fertilization, wall of ovary thickens to form
fruit.
 Fruit helps protect seeds while they disperse.
 Some fruits, like dandelion, are modified to
catch wind.
 Burrs that stick to animals - fruits.
 After fertilization, fruit triggered to
form.
 Wall of ovary becomes pericarp
(thickened wall of fruit)
 If flower not pollinated, fruit will not
develop.
 3 different types of fruits.
 1Simple fruits - single ovary, like cherries.
 2Aggregate fruit, blackberry - single flower
with several carpals.
 3Multiple fruit, pineapple - develops a tightly
clustered group of flowers.
 Ovules (develop in ovary) contain female
gametophyte (the embryo sac)
 Angiosperm life cycle starts with
mature flower on sporophyte plant, ends
with germinating seed.
 Anther produce microspores - form
male gametophytes (pollen).
 Ovules produce megaspores - form
female gametophytes (embryo sacs).
 Pollen released from anther - carried
to sticky stigma of carpal.
 Plants can self-pollinate; crosspollination is better.
 Pollen grain begins growing from stigma
toward ovary.
 Discharges 2 sperm cells into female
gametophyte.
 1 sperm fuses with egg nucleus to form
diploid zygote - develops into embryo.
 Embryo has rudimentary root and 1 (in
monocots) or 2 seed leaves (in dicots),
(cotyledons)
 Other sperm nucleus fuses with 2 polar bodies to
form endosperm, (triploid or 3n) in monocots.
 Dicots - nutrition goes directly to cotyledons.
 As ovules develop into seeds, ovary develops into
fruit.
 Conditions favorable, germination occurs - seed
coat ruptures and embryo emerges as seedling.
 Seedling uses food stored in either
endosperm (monocot) or cotyledon
(dicot) to start growth.
 As seed develops, enters dormancy
allows it to survive until conditions
are favorable.
 1st organ to emerge from germinating
seed is radicle (embryonic root)
Asexual reproduction
 Plants can clone themselves - vegetative
reproduction.
 Fragmentation - parent plant separates
into parts that reform whole plants.
Co-evolution
 Because certain animals only eat certain
plants, actually have forced evolution of
one another.
 Plants have evolved special fragrances,
that forced evolution of specific animals
to pollinate these plants.
Plants and human welfare
 All our fruit and vegetable crops are
angiosperms.
 Corn, rice, wheat, and other grain are
grass fruits.
 Plants for medicinal purposes; more than
25% of our prescriptions come from
plants.
 Destroying these plants may mean
destroying possible cures.
Biotechnology
 Selective breeding has allowed humans
to spread plants that could not survive
for very long (i.e. maize).
 Scientists use transgenic plants,
(genetically engineered to express
foreign gene from another species) to
study genetics.