life in water vs. life on land - nassau community college
TRANSCRIPT
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Origin and Evolution of Plants: Algae
• Green algae – closest relatives to
modern terrestrial plants (outgroup)
– Chlorophyll
– Cell walls composed of cellulose
– Starch = primary NRG reserve
• Photosynthetic and often multicellular
Life in Water vs. Life on Land• Life in water is pretty easy compared to life on
land…
• Why?– Bathed in fluid—don’t worry about desiccation!
– Algae are surrounded by medium from which they get nutrients and O2---no need for long distance transport in plant!
– Algae supported by surrounding water, gravity not a problem.
– Gametes and adults can disperse (or swim)
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Plant Adaptations to Life on Land
• Life on land offered new opportunities
– Unlimited sunlight
– Abundant CO2
– Initially, few pathogens or herbivores
• Land plants are a clade, defined by a set
of derived characters
– Alternation of haploid and diploid generations
–Walled spores produced in sporangia
– Male and female gametangia
– Multicellular, dependent sporophyte embryos
Today’s Goals
• Four major groups of land plants
• Origin of major plant characteristics
• Each group represents a different major evolutionary radiation associated with increasing adaptations to life on land.
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The Mosses: Bryophytes
• Exhibit two crucial adaptations to life on land
– Cuticle reduces desiccation
– Protection of the embryo: retained on the “maternal plant”
• Still restricted to moist habitats
– Lack a well developed vascular system
– Fairly little structural support
– Rely on moisture for sperm to reach the eggs
• Haploid gametophyte more conspicuous than Diploid sporophyte.
• Only plant group where dominant form is the haploid gametophyte.
• Water is required in order for the flagellated sperm to reach the egg. The sporophyte is tiny and attached to the moss plant. Water is required in order for spores to germinate and form a new gametophyte moss plant.
http://www.sbs.auckland.ac.nz/info/schools/nzplants/con_reproduction.htm
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The Ferns
(Second Radiation of Land Plants)
• Tracheophyta
– In addition to a cuticle and protected embryo, ferns have
• Well developed vascular tissues for transport within
• Vascular system invested with lignin (structural support)
• Can now get large (some early seedless plants > 40m)
– But…
• Still rely on water for transport of gametes
• Sporophyte more conspicuous than gametophyte
• Dominant form is the diploid sporophyte
• Water is required in order
for spores to germinate and form a tiny thumbnail-sized
gametophyte on the soil surface.
Water is required in order for the flagellated sperm
to locate an egg.
http://www.sbs.auckland.ac.nz/info/schools/nzplants/con_reproduction.htm
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• Seedless plants formed vast ancient forests in
low-lying wetlands during the Carboniferous
period (360–299 million years ago)
– When they died, the plants formed peat deposits that eventually formed coal
• Coal, oil, and natural gas are fossil fuels
– Oil and natural gas formed from marine organisms; coal formed from seedless plants
– Burning fossil fuels releases CO2, causing climate warming
Gymnosperms & the 3rd Radiation
• ~ 700 living species
• In addition to cuticle, protected embryo, vascular tissue for transport and support…
– Seed
• Embryo enclosed in durable, desiccation resistant seed.
Can wait for favorable conditions to develop and can be
dispersed.
– Reduced Gametophyte.
• Male gametophyte small enough to be dispersed by
wind!
• REPRODUCTION FREE FROM WATER!
• Heterosporous (Produce two types of spores)
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Sporangia producespores; spores developinto pollen grains.
Spore mother cell (2n)
Meiosis
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Sporangium (2n)
Scale
Integument
Pollination
Ovule
Meiosis
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3Pollen grains(male gameto-phytes) (n)
Ovulate conebears ovules.
Haploid (n)
Diploid (2n)
Key
Mature sporophyte
Egg (n)
Fertilization
Femalegametophyte (n)
Male gametophyte (pollen grain)
Sperm (n)
A haploid spore celldevelops into femalegametophyte, whichmakes eggs.
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Pollen growstube to eggand makesand releasessperm.
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Seed coat
Zygote(2n)
Zygote developsinto embryo, andovule becomes seed.
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Food supply
Embryo (2n)Seed
7 Seed germinates,and embryo grows into seedling.
Pollination in gymnosperms• In pollination, a pollen grain lands on a scale
in an ovulate cone and enters an ovule
• Fertilization occurs a year after pollination,
when a sperm moves down a pollen tube to the
egg to form a zygote
– The zygote develops into a sporophyte embryo, and the ovule becomes a seed, with stored food and a protective seed coat
• The seed is a key adaptation for life on land
and a major factor in the success of seed plants
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Angiosperms & the 4th Radiation
• ~250,000 living species
• Reasons for this diversification may include– A more complex and efficient vascular system
– Ovules protected in ovary
– Fruit promoting dispersal• Eat and poop – move the seeds!
• Types of fruits
• Flowers and insects (don’t have to rely on just wind)– Recruit other organisms to work for them!
• The gametophytes is even more reduced than in Gymnosperms – seeing a trend here?
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Pollination
• 90% of angiosperms use animals to transfer pollen– Birds are attracted by colorful flowers, but not
scent
– Beetles are attracted by fruity odors, but not color
– Bats are attracted by large, highly scented flowers
–Wind-pollinated flowers produce large amounts of pollen
Meiosis
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Haploid (n)
Diploid (2n)
Key
Egg (n)
Fertilization
Sperm
Seed coat
Zygote(2n)
Food supply
Embryo (2n)
Seeds
Haploid spores in anthers develop intopollen grains: male gametophytes.
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Meiosis
Pollen grains (n)
Ovule
Haploid spore in each ovuledevelops into female gameto-phyte, which produces an egg.
3 Pollination andgrowth of pollen tube
Stigma
Pollen grain
Pollen tube
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Fruit(matureovary)
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Seed5
Ovary
Ovule
Stigma
Anther
Sporophyte (2n)
Seed germinates,and embryogrows intoplant.
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Angiosperms
• Flowers contain separate male and female sporangia and gametophytes
• Flowers usually consist of sepals, petals, stamens (which produce pollen), and carpels(which produce eggs)– Sepals enclose and protect the flower before it opens
– Petals attract animal pollinators
• Stamens include a filament and anther, a sac at the top of each filament that contains male sporangia and releases pollen
Angiosperms
• The carpel is the female reproductive
structure, including the ovary
– The ovary encloses the ovules, which contain sporangia that will produce a female gametophyte
• Ovules develop into seeds; ovaries mature
into fruit
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Stamen
Anther
Filament
Petal
Receptacle
Ovule
Sepal
Stigma
Style
Ovary
Carpel
Ovary, containingovule
Mature plant withflowers, wherefertilization occurs
Fruit (mature ovary),containing seed
Embryo
Seed
Germinatingseed
Seedling
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Seeds
• The zygote divides many times via mitosis to produce the embryo
• The embryo consists of tiny root and shoot apical meristems and one or two cotyledons
• A tough seed coat develops
• Seed dormancy
– Embryo growth and development are suspended
– Allows delay of germination until conditions are favorable
Cotyledon
Cotyledons
Embryonicshoot
EmbryonicShoot
Embryonicroot
EndospermEmbryonicleaf
Fruit tissue
Seed coat
Sheath
Corn (monocot)
Common bean (eudicot)
Seed coat
Embryonicroot
Embryonicleaves
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MONOCOTS
EUDICOTS
Seed leaves Leaf veins Stems Flowers Roots
Onecotyledon Veins usually parallel
Vascular bundles in
complex arrangement
Floral parts usually
in multiples of threeFibrous
root system
Taprootusually present
Floral parts usually inmultiples of four or five
Vascular bundlesarranged in ringVeins usually branched
Twocotyledons
• Dicots—most plants• Two cotyledons
• Branched leaf
venation
• Ring of vascular bundles
• Flower parts in 4s or 5s (or multiples)
• Taproot system
– Monocots• One cotyledon
• Parallel leaf venation
• Scattered vascular
bundles
• Flower parts in 3s or multiples of 3
• Fibrous root
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Ovary, containingovule
Mature plant withflowers, wherefertilization occurs
Fruit (mature ovary),containing seed
Embryo
Seed
Germinatingseed
Seedling
Fruits
Hormonal changes induced by fertilization
trigger the ovary to develop into a fruit
• Fruits are adaptations that disperse seeds
– Some rely on wind for seed dispersal
– Some hitch a ride on animals
– Fleshy, edible fruits attract animals
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Upper partof carpel
Ovule
Ovarywall
Sepal
Seed
Pod(opened)
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• Most human food is provided by the fruits
and seeds of angiosperms
– Corn, rice, wheat, and other grains are dry fruits
– Apples, cherries, tomatoes, and squash are
fleshy fruits
– Spices such as nutmeg, cinnamon, cumin, cloves, ginger, and licorice are also angiosperm fruits
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Spores
Flagellatedsperm
Stem Leaf
Seed
Pollen
Leaf
FernStomata; roots anchor plants,absorb water; lignified cellwalls; vascular tissue;fertilization requires moisture
Roots
Stem
Roots
Pine treeStomata; roots anchor plants, absorb water; lignified cell walls; vascular tissue;fertilization does not require moisture
MossStomata only on sporophytes; primitive roots anchor plants,no lignin; no vascular tissue;fertilization requires moisture
Spores
Flagellatedsperm
Leaf
Stem
Roots
Flagellatedsperm
Vasculartissue
Key
Holdfast(anchors alga)
AlgaWater supportsalga. Whole algaperforms photo-synthesis;absorbs water,CO2, andminerals fromwater.
Shoot system
(photosyntheticcenter)
Root system(anchors,
absorbsnutrients,
and stores
food)
Root hairs
(microscopic;increase surface
area for absorption)
Leaf (mainphotosynthetic organ)
Blade
Petiole
Node
Internode
Axillary bud (produces a branch)
Stem (supports leavesand flowers)
Terminal bud (grows stem)
Flower (reproductive organ)
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Typical Plant Body
– Plants absorb water and minerals from soil through roots
– Plants absorb the sun’s energy and carbon dioxide from the air through shoots (stems and leaves)
– Plant roots depend on shoots for carbohydrates produced via photosynthesis
– Plant shoots depend on roots for water and minerals
Typical Plant Body
• Plant roots
– Anchor plant
– Absorb water and nutrients
– Store food
• Plant shoots
– Stems, leaves, and reproductive structures
– Stems provide support
– Leaves carry out photosynthesis
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Plant Body Modifications
• Modifications of plant parts are
adaptations for various functions–Food or water storage
–Asexual reproduction
–Protection
–Climbing
–Photosynthesis
Root Modifications
• Food Storage
– Large taproots store starches
– carrots, turnips, sugar beets, sweet potatoes
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Stem modifications
• Stem modifications
– Stolon: asexual reproduction
– Rhizomes: storage, asexual reproduction
– Tubers: storage, asexual reproduction
– Cactus stem: water storage
& photosynthesis
Leaf modifications
– Protection–Cactus spine
–Climbing– Pea plant tendril
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Three tissue systems in the plant body
• Dermal tissue
– Outer protective covering
– Layer of tightly packed cells called the epidermis
– First line of defense against damage and infection
– Waxy layer called cuticle reduces water loss
• Vascular tissue
– Support and long-distance transport (xylem, phloem)
• Ground tissue
– Bulk of the plant body
– Food production, storage, support
Eudicot leaf
XylemPhloem
Vein
Guardcells
Stoma
Sheath
Eudicot stemVascularbundle
Pith
Cortex
Epidermis
Eudicot root
Endodermis
Cortex
Epidermis
PhloemXylem Vascular
cylinder
Mesophyll
Cuticle
Upper epidermis
Lower epidermis
Monocot stem
Vascularbundle
Epidermis
Key
Ground tissue systemDermal tissue system
Vascular tissue system
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Xylem and Phloem
• Xylem
– Transports water throughout plant
• Phloem
– Transports food throughout plant
Plant vs. Animal cells
• Plants cells have three structures that
distinguish them from animals cells
– Chloroplasts used in photosynthesis
– A large, fluid-filled vacuole
– A cell wall composed of cellulose
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How do plants grow?
• Animal growth is determinate
– Growth stops after a certain size is reached
• Plant growth is indeterminate
– Growth occurs throughout a plant’s life
– Plants are categorized based on how long they live
–Annuals complete their life cycle in one year
–Biennials complete their life cycle in two years
– Perennials live for many years
Primary Growth
• Plant growth occurs in specialized tissues called meristems– Regions of active cell division
• Apical meristems are found at the tips of roots and shoots–Where primary growth occurs
– Primary growth allows roots to push downward through the soil and shoots to grow upward toward the sun
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Primary Growth
• The apical meristems of shoot tips occur as buds at the stem tip and at the base
of leaves
• Cells produced in the shoot apical meristem differentiate into dermal, vascular and ground tissues
Axillary buds
Terminal bud
Arrows =directionof growth
Roottips
Secondary Growth
• Plants grow thicker over time
• Secondary growth occurs at lateral meristems
– areas of active cell division that exist in two cylinders that extend along the length of roots and shoots
– Vascular cambium is a lateral meristem that lies between primary xylem and phloem
– Cork cambium is a lateral meristem that lies at the outer edge
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Secondary Growth
• Vascular cambium produces cells in two directions– Secondary xylem produces wood toward the
interior of the stem
– Secondary phloem produces the inner bark toward the exterior of the stem
• Cork cambium produces cells in one direction– Cork cambium produces the outer bark
Secondary xylem(2 years’ growth)
Growth
Shedepidermis
Year 1Late Summer Key
Ground tissue system
Dermal tissue system
Vascular tissue system
GrowthGrowth
Year 2Late Summer
Year 1Early Spring
Bark
Secondaryxylem (wood)
Secondaryphloem
Corkcambium
Cork
Primaryphloem
Primaryxylem
Vascularcambium
Epidermis
Cortex
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Secondary Growth
• Most transport occurs near the vascular
cambium
– Sapwood near the vascular cambium transports water
– Heartwood stores resins and wastes
– Transport of sugars occurs in the secondary phloem near the vascular cambium
Sapwood
Heartwood
Bark
Rings
Woodrays
Heartwood
Sapwood
Vascular cambium
Secondary phloemCork cambiumCork
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Secondary Growth
• Wood annual rings show layers of secondary
xylem
– In temperate regions, periods of dormancy stop growth of secondary xylem
– Rings occur in areas when new growth starts each
year
• The bark (secondary phloem and cork) is
sloughed off over time
Reproductive structures, as in flowers,contain spores and gametes
Cuticle covering leaves and stemsreduces water loss
Stomata in leaves allow gas exchangebetween plant and atmosphere
Lignin hardens cell walls of someplant tissues
Stem supports plant; may performphotosynthesis
Vascular tissues in shoots and rootstransport water, minerals, and sugars;provide support
Leaves carry out photosynthesis
Roots anchor plant; mycorrhizae (root-fungus associations) help absorb waterand minerals from the soil
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Copyright © 2009 Pearson Education, Inc.
Plants and Fungi
– Plants and fungi colonized land together
– Mycorrhizae, mutually beneficial associations of plant roots and fungi hyphae, enabled plants to colonize land– Mycorrhizal fungi absorb water,
phosphorus, and other minerals from soil and make them available to the plant
– The sugars produced by the plant nourish the fungus
Fungi
• Fungi are absorptiveheterotrophic eukaryotes that digest their food externally and absorb the nutrients
• Most fungi consist of a mass of threadlike hyphae making up a mycelium
• Fungal hyphae are surrounded by a cell wall with chitin
Hypha
Mycelium
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Fusion of cytoplasm
Heterokaryoticstage
Spore-producingstructures
Asexualreproduction
Spores(n)
Diploid (2n)
Haploid (n)
Heterokaryotic (n + n)(unfused nuclei)
Key
Sexualreproduction
Zygote(2n)
Fusion of nuclei
Spore-producingstructures
Spores (n)
Mycelium
Meiosis
Germination
Germination
Chytrids
Zygomycetes(zygote fungi)
Glomeromycetes(arbuscularmycorrhizal fungi)
Ascomycetes(sac fungi)
Basidiomycetes(club fungi)
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Chytrids
• Chytrids, which have flagellated spores, are the earliest lineage of fungi
• In 1999, a new species was described that infects amphibians and causes a deadly disease.
• Travels easily on water and moist surfaces
• Where the fungus thrives, 50% of amphibian species and 80% of individuals can be expected to disappear within one year (Lips et al. 2006)
• 80% of plant diseases are caused by fungi– Between 10 and 50% of the world’s fruit harvest is
lost each year to fungal attack
– A variety of fungi, including smuts and rusts, infect grain crops
• Only 50 species of fungi are parasitic on animals, causing mycoses– Human infections include athlete’s foot (caused by
ringworm)
– Systemic mycoses are rare but serious fungal infections that spread through the body from inhaled spores
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Lichens
• Lichens consist of algae or cyanobacteria within a fungal network
– Many lichen associations are mutualistic
– The fungus receives food from its photosynthetic partner
– The fungal mycelium helps the alga absorb and retain water and minerals
• Lichens are important pioneers on new land, where they help to form soil
– Lichens are sensitive to air pollution, because they obtain minerals from the air
For Next Week
• Lab– Invertebrate questions due at 8:40 AM
– Bring dissecting kit and gloves to lab
• Lecture – Assignment: Collect 5 branches from trees, put in
plastic bags – For each,• Identify if it is from a gymnosperm or an angiosperm
• Try to identify the tree – common name and latin name
– Extra credit: 1-2 page earthworm paper with references