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Transition to Land &Life Cyclesy
What does it mean to be a plant?Lecture 1
Background
• Descendants of charophytan green algae• Photosynthesis• Modular growth (mitosis & apices)• Sexual Reproduction in Eukaryotes• Three basic life cycles
Plants from Algae
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Chlorophytes never made it to land
Charophytes did
Volvox-Colonial chlorophyte
-Hollow sphere of i l l fa single layer of
500-60,000 cells-A few cells are specialized for reproduction
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CharophytesCharales (300 species)
-Macroscopic-Plant-like plasmodesmataS-Sister clade to land plants
Choleocaetales (30 species)-Microscopic-Plant-like mitosis-Next closest plant relatives
Charophytes (Cont.)
Bryophytes
Bryophytes are the closest living descendants of the first land plants.-Called nontracheophytes because they lack tracheids (specialized transport cells)lack tracheids (specialized transport cells)
Simple, but highly adapted to diverse terrestrial environments.
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Photosynthesis• Complete and balanced equation:
3CO2 + 6H2O Light
C3H6O3 + 3O2 + 3H2O
Occurs in two stages:Light & Dark Reactions
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Primary Photosynthetic Pigments
• Pigments absorb light• Chlorophyll makes leaves green, absorbs
light in the visible spectrum.R fl t li ht• Reflects green light– Therefore appears green
Primary Pigments
• Chlorophyll a– All photosynthetic eukaryotes & cyanobacteria
• Chlorophyll b– Plants green algae & euglenoid algaePlants, green algae, & euglenoid algae– Accessory pigment (not directly involved in
photosynthetic energy transduction)– Broadens the range of light for photosynthesis
• Chlorophyll c– Takes place of chlorophyll b in some algae
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Chlorophyll a
CHO
Chlorophyll b
Two other pigments
• Carotenoids (anti-oxidants protecting chlorophyll)– Red, orange, or yellow lipid-soluble pigments
• Found in chloroplasts & cyanobacteria• Hydrophobic
• Two groups– Carotenes & Xanthophylls
• Carotenoids break down giving rise to….?
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http://rawsilkandsaffron.files.wordpress.com/2010/10/fall_colors.jpg
• Phycobilins– Found in cyanobacteria & chloroplasts of red
algae– Water solubleWater soluble
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Modular Growth
• Indeterminate growth– Grow through entire life– Add new body parts
Repeated addition of– Repeated addition of same basic units
• Above ground– Bud-stem-leaf units
• Below ground– New lateral roots
Primary Growth• Plants increase in length by primary growth.• Meristems
– Group of young, undifferentiated cells– Give rise to new cells
A i l i t• Apical meristem– Increase in length
• Shoot apical meristem• Root apical meristem• Cell division results in two cell populations
– Remain undifferentiated meristematic cells– Rapidly dividing new growth descendent cells
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Eukaryotic Reproduction
Life Cycles 2
Sexual Reproduction
• Alternation between meiosis & fertilization• Meiosis = Reduction from 2n – n.• Fertilization = n + n = 2n
Meiosis
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Steps in meiosis • Prophase I: Chromosomes come together, pairs
coil, become shorter.• Metaphase I: Move to metaphase plate.• Anaphase I: Paired chromosomes move to
opposite poles.pp p• Metaphase II: Chromosomes lined up at the
equatorial plane.• Anaphase II: Centromeres separate, move toward
opposite poles of spindles.• Telophase II: Completed migration. Four new
haploid nuclei are formed.
• Meiosis differs from Mitosis in 3 ways.1. Two nuclear divisions in meiosis. In both
DNA only replicated once.2 Nuclei produced in meiosis is haploid (1/22. Nuclei produced in meiosis is haploid (1/2
the number of chromosome). 3. Meiosis results in different gene
combinations.
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Inheritance
• Allele– Alternative form of a gene.– Occupy same site on homologous
chromosomes (locus)chromosomes (locus).
Gregor Mendel
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Plant Life Cycles
Lecture III
Life Cycles
• Three types1. Gametic meiosis2. Zygotic meiosis3 Sporic meiosis3. Sporic meiosis
Gametic life cycle
• Animal kingdom (some protists & algae)– The gamete is the only haploid cell produced.
meiosis fertilization mitosis2n
multicelled1n
gamete2n
zygote2n
multicelled
meiosis fertilization mitosis
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Zygotic life cycle
• Fungi Kingdom– The zygote is the only diploid cell produced
mitosis fertilization meiosis mitosis1n
multicelled1n
gamete2n
zygote1n
spore 1nmitosis fertilization meiosis mitosis
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Allomyces arbusculus
Rhizopus stolonifer, Zygomycete
Ascomycetes
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Basidiomycota
Sporic life cycle
• Plant Kingdom– Alternation of generations (plants, many
algae)• Gametophyte = haploid gamete producing• Gametophyte = haploid, gamete-producing
generation.• Sporophyte = diploid, spore-producing
generation.
2n sporophyte
1n spore
1ngametophyte
1ngamete
2nzygote
meiosis mitosis mitosis fertilization
mitosis
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Bryophytes
Pterophytes
Gymnosperms
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Angiosperms
