Division: Chlorophyta – Green Algae
Very important from an evolutionary point of view
Some formed complex multicellular bodies
Moved onto land – later to become “true” plants
• Body Construction in the Green Algae – simplest is a
motile unicellular organism – from this simple plan
several paths were taken
– Motile colonies
• Cells adhere to one another
• All cells are similar
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Division: Chlorophyta – Green Algae
– Nonmotile Colonies
• Cells either never develop
flagella or flagella is lost
• Flagella considered the
ancestral trait
– Filamentous Body
• Cells held together via middle
lamella
• Cell division transverse; if
longitudinal results in filament
branching
• Parts can be specialized
» Holdfast
» Gamete production
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Division: Chlorophyta – Green Algae
• Membranous Body
– Cell division occurs in only two
planes
• Forms a thin sheet of cells
• Easily torn by wave action
• Parenchymatous Body
– Cell division occurs in three
planes
• Cells connected by
plasmodesmata
• True parenchyma tissue is
formed
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Division: Chlorophyta – Green Algae
•
Coenocytic or Siphonous Body
– Karyokinesis without cytokinesis; results in a giant multinucleate
cell
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Life Cycles of the Green Algae
• Asexual Reproduction – ex. Euglenoids
– Cell cycle – mitosis and cytokinesis
• Sexual Reproduction
– Requires meiosis
– Requires syngamy
– Simplest form
• Dipoloid cell undergoes meiosis
– Haploid individuals produced that can reproduce via mitosis
– Some cells act as gametes and fuse
» Produces a diploid cell that can reproduce via mitosis
• Very little difference between diploid and haploid individuals
• Referred to as being DIBIONTIC (alternation of generations
between haploid and diploid)
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Life Cycles of the Green Algae
– Monobiontic Species - Only one
free-living generation
• Example #1
– Haploid phase only
represented by the individual
» Can be either uni or
multicellular
» Carries out photosynthesis
and growth
– Only diploid cell is the
zygote
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Life Cycles of the Green Algae
• Example #2
– Diploid phase represents the
individual - undergoes
vegetative growth
– Haploid cells are gametes
which undergo syngamy
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Life Cycles of the Green Algae
• Isomorphic vs Heteromorphic Generations
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Life Cycles of the Green Algae
• Gamete Development
– Early on gametes were
identical, isogamous
– Later anisogamy developed
(slight difference)
– Ultimately oogamy evolved
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Representative Genera of the Green Algae
• Unicellular Species – ex. Chlamydomonas
–
–
–
–
Chlorophylls a and b, carotenoids, xanthophylls
Starch produced in chloroplasts
Two anterior flagella (common to most motile green algae)
Reproduces via mitosis, meiosis + syngamy
•
•
•
•
Haploid resorbs flagella
Divides mitotically producing either 2, 4, 8, or 16 cells
Each new cell grows a two flagella
These cells swim and eventually meet another cell
– Plasmogamy and karyogamy produce a single large zygote
(only diploid cell)
– Becomes dormant
– Germinates via meiosis, producing four haploid individuals
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Representative Genera of the Green Algae
• Motile Colonial Species – cell closely resemble
Chlamydomonas – after zygote divides individuals are
held together by a gelatinous mass
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Representative Genera of the Green Algae
– Based upon advances
• Gonium
– Colonies small (4 – 32 cells)
– Simple organization, flagella beat in synchrony
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Representative Genera of the Green Algae
• Pandorina
– Similar in size to Gonium
– Some differentiation, anterior cells slightly different than
posterior cells, causes colony to swim in one direction
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Representative Genera of the Green Algae
• Volvox
– up to 50,000 cells (can see colony without a microscope)
– Group of anterior cells, about 50, modified for reproduction
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Representative Genera of the Green Algae
•
Filamentous Species
– Ulothrix
• Monobiontic
• A single row of cells, with terminal cell modified to a holdfast
• Zoospores can be produced mitotically
– Possess four flagella
– Settle to bottom
– Germinate into new filaments
• Some cells produce gametes
– isogamous
– Two flagella, resemble Chlamydomonas
– Fuse producing a zygote which germinates via meiosis
producing haploid zoospores
– Settle to the bottom and germinate into a filament
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Representative Genera of the Green Algae
– Syrogyra
• Very common if freshwater
environments
• Chloroplast spirally arranged
• No swimming gametes; rather
a conjugation tube
• Each filament is haploid (+ or -)
• Zygote becomes dormant and
thick walled
• Germinates into a new filament
from haploid spores
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Representative Genera of the Green Algae
• Laminar Species
– Ulva
• Similar to Ulothrix
• Cell germinate in two
planes
• Dibiontic life cycle
(alternation of isomorphic
generations)
• Separate individuals
producing different
gametes, dioecy
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Representative Genera of the Green Algae
• Coenocytic Species
– Dibiontic life cycle
– Heteromorphic generations
(initially caused real
problems)
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Representative Genera of the Green Algae
• Parcnchmatous Species – some types divide via a
phragmoplast (plants do this) possibly ancestral
– Chara – has multicellular gametangia (plant or not)
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Division Phaeophyta: Brown Algae
• Major Characteristics
– Mostly marine, in littoral zone (between high and low tides)
– Very complex anatomically and morphologically
– Similar to plants but very different
• Possess chlorophylls a and c, fucoxanthin, violaxanthin,
diatoxanthin and carotenes (implications?)
• Storage product is laminarin (glucose polymer), mannitol and fat (no
starch)
• Have a holdfast, stipe (stalk) and a blade
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Division Phaeophyta: Brown Algae
• Cell walls contain cellulose and alginic acid (used in paint an food
industry)
• Can be very large, and have developed specialized regions
– Holdfast, anchoring
– Epidermis to prevent damage from waves
– With an epidermis diffusion is impaired, need a conducting
system
» Have trumpet cells that resemble phloem (convergence)
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Division Phaeophyta Brown Algae
– Ectocarpus
• Isomorphic generations
• Diploid sporophytes possess unilocular sporangia at the ends of
small terminal branches
– First nuclear division is via meiosis (haploid)
– Zoospores germinate into gametophyte
»
»
»
»
Ends of branches are gametangia
Plurilocular gametangia
Gametes anisogamous
Settle to the bottom secrete ectocarpene, attracts opposite,
syngamy ensues
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Division Phaeophyta Brown Algae
– Fucus
•
•
•
•
Common on rocks of intertidal zone
Diploid individuals seen at low tide
Dichotomously branched blades
Ends of branches posses
receptacles that contain concepticles
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Division Rhodophyta: Red Algae
• Major Characteristics
– Large group – 3,900 sp.
– Very different from other algae and true plants
• Like cyanobacteria have phycobilin (accessory pigment)
• Typically red (phycoerythrin) can be purple, brown or black (phycocyanin),
chlorophyll a and carotenoids
• Storage product floridean starch, similar to glycogen
• Different sugars formed
• Cell wall contains cellulose and sulfated galactans (slimy mucilages) – used
to produce agar
• No plasmodesmata
• Mostly multicellular
• Life cycles poorly known
– Unique, lack any motile cells
– Lack centrioles but have polar rings for this function
– Polysiphonia – three phases to its life history
» Haploid gametophyte
» Diploid carposporophyte
» Diploid tetrasporophyte
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