Multicellular
Algae – Ch.6
Kingdom Protista
Developed by Dave Werner
Video Clips
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YouTube – Plankton
YouTube – Blue Planet (Fish Larva)
YouTube – Kelp Forests
YouTube – Giant Kelp
• Great Kelp Forrest Video
Characteristics of Algae:
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Plantlike members of the kingdom Protista
Eukaryotes
Most unicellular, but some multicellular
Autotrophic – contain chlorophyll & make food by
photosynthesis
Planktonic
Produce oxygen
microscopic to seaweeds hundreds of feet in length
Do not have true roots, stems, nor leaves
Form gametes (eggs & sperm) in single-celled gametangia
(chambers) instead of multicellular gametangia like true plants
Found in freshwater, marine, and moist soil habitats
Most have flagella at some time in life cycle
Algae cells contain organelles called pyrenoids organelles that
make & store starch
Structure of Algal Cells:
• The body of algae is called the thallus
• Algae may be unicellular, colonial,
filamentous, or multicellular
• Unicellular algae are single-celled & make up
phytoplankton (a population of
photosynthetic organisms that begins many
aquatic food chains)
• Phytoplankton make much world's
carbohydrates & are the major producers of
oxygen
Structure of Seaweeds
• Filamentous algae have
slender, rod-shaped
thallus arranged in
rows joined end-to-end
• Holdfasts are
specialized structures
in some filamentous
algae that attaches the
algae so it can grow
toward sunlight at the
surface
Structure of Seaweeds:
• Multicellular
algae often have a
large, complex leaflike thallus & may
have stem-like
sections and air
bladders called
pneumatocysts
• Macrocystis is
among the largest
multicellular algae
Structure of algae vs. seagrass
Filamentous algae
Enteromorpha
Multicellular algae
Macrocystis
Classification:
• Algae are classified into 3 phyla, based
on color, type of chlorophyll, form of
food-storage substance, and cell wall
composition
• All phyla contain chlorophyll a
• Many species of algae reproduce
sexually and asexually
• Sexual reproduction in algae is often
triggered by environmental stress
Chlorophyta (green Algae): 7000
species
• May be unicellular, multicellular, or colonial
• Include Spirogyra, Ulva, & Chlamydomonas
• Contain chlorophyll a & chlorophyll b and
carotenoids (orange & yellow pigments) as
accessory pigments
• Store food as starch
• Cell = cellulose, some add CaCO3
• Habitat -freshwater, moist surfaces, or marine
environments
• Some have whip-like flagella for movement
• May live symbiotically as lichens
• Thought to have given rise to terrestrial plants
Phaeophyta (brown algae): 1500
species
• Contain chlorophyll a & chlorophyll c and
fucoxanthin (brown pigment) as accessory pigments
• Most multicellular- growing in cooler marine habitats
• Includes kelps & seaweeds
• Largest protists
• Specialized rootlike holdfasts
• Specialized air bladders
• Stemlike structures are called the stipe
• Store food as a carbohydrate called laminarin
• Include Laminaria & Fucus
Rhodophyta (red algae): 4000
species
• Multicellular algae that mainly grow deep in warm
marine waters
• Some freshwater species exist
• Highly branched thallus
• Contain chlorophyll a & phycobilins (red pigments)
to trap sunlight
• Store food as starch
• Cell walls contain cellulose and agar (used as a base
in culture dishes to grow microbes)
• Some species contain carageenan in their cell walls
used for gelatin capsules & in some cheeses
Common Marine algae of Barnegat
Bay
Enteromorpha
Ulva lactuca
(Sea Lettuce)
Agardhiella
Fucus
(rockweed)
spongomorpha
Sargassum
A closeup of a small mass of sargassum weed. The numerous small
round spheres are floats filled with carbon dioxide. These provide
buoyancy to the algae.
There are numerous types of
marine algae found throughout our
back bay areas, this has just been
a sample of what you will find.
Diatom Reproduction
fig. 5.7 (p.95)
Asexual = Cell Division into Auxospores
• Produces Blooms
Sexual = Egg & Sperm
Reproduction in Unicellular
Algae
Bio book p.510-513
Asexual Phase
• Algae absorbs its flagellum
• Haploid algal cell then divides
mitotically from 2 to 3 times
• From 4 - 8 haploid flagellated cells
called zoospores develop in this parent
cell
• Zoospores break out of the parent cell
& eventually grow to full size
Sexual Phase
• Haploid cells dividing mitotically to produce
either “plus” or “minus” gametes
• A plus gamete and a minus gamete come
into contact with one another, shed their cell
walls, and fuse to form a diploid zygote
• This resting stage of a zygote is called a
zygospore & can withstand bad
environmental conditions
• When conditions are bad, the thick wall
opens and the living zoospore emerges
Chlamydomonas (fig. 25-3)
Reproduction in Multicellular
Algae:
• Oedogonium is a multicellular, filamentous green
algae with specialized cells called gametangia that
form gametes
• The male gametangia or antheridium makes sperm,
& the female gametangia or oogonium makes eggs
• Sperm are released into the water & swim to the egg
to fertilize them
• The fertilized egg or zygote is released from the
oogonium & forms thick-walled zoospores
• Zoospores undergo meiosis so one cell attaches to
the bottom & develops a holdfast while the other
zoospores divide & form a filament
Spirogyra, another filamentous
green algae, reproduces by
conjugation
Two filaments align side by side, their adjacent cell walls dissolve, & a
conjugation tube forms between them
Fertilization occurs when a + gamete cell moves through the tube & fuses
to the - gamete cell
Zygote forms a thick walled spore (sporangium) that breaks away from
the parent & forms a new filament
Conjugation Tube between Spirogyra
Ulva fig.6.11
• The leaflike algae Ulva has a sexual
reproductive cycle characterized by a pattern
called alternation of generations
• Alternation of generations has two distinct
multicellular phases- a haploid, gameteproducing phase called a gametophyte and a
diploid, spore-producing phase called a
sporophyte
• Alternation of Generation also occurs in
more complex land plants, but the
gametophyte & sporophyte do not resemble
each other