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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