20-4 Plantlike Protists: Red,
Brown, and Green Algae
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
20-4 Plantlike Protists: Red, Brown,
and Green Algae
The three phyla of algae that are largely multicellular
are:
• red algae
• brown algae
• green algae
The most important difference among the multicellular
algae involves their photosynthetic pigments.
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Red Algae
Red Algae
Members of the phylum Rhodophyta, “red plants.”
Live at great depths due to their efficiency in
harvesting light energy.
Contain chlorophyll a and reddish accessory
pigments called phycobilins.
Phycobilins absorb blue light, enabling red algae to
live deep in the ocean.
Many red algae appear green, purple, or reddishblack.
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Red Algae
Red algae can be found from the polar regions to the
tropics.
They can grow anywhere from the ocean’s surface
down to depths of 260 meters.
Most are multicellular and all have complex life cycles.
Lack flagella and centrioles.
Help in formation of coral reefs by maintaining
equilibrium through nutrients from photosynthesis.
It also provides much of the calcium carbonate that
helps to stabilize a growing coral reef.
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Brown Algae
Brown Algae
Phylum Phaeophyta, “dusky plants.”
Brown algae contain chlorophyll a and c, as well as
a brown accessory pigment, fucoxanthin.
Dark yellow-brown color
Largest and most complex of the algae
All are multicellular, most are marine
Commonly found in cool, shallow coastal waters of
temperate or arctic areas.
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Brown Algae
Largest known alga is giant kelp, a brown alga that
can grow to more than 60 meters in length.
Another brown alga,Sargassum, forms huge floating
mats many kilometers long in an area of the Atlantic
Ocean near Bermuda known as the Sargasso Sea.
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Fucus, a common brown
alga also known as rock
weed, is made up of a
holdfast, stipes,
bladders, and blades.
Brown Algae
Blades
The holdfast attaches the
alga to rocks.
Holdfast
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Brown Algae
The body of Fucus
contains:
a flattened stemlike
structure called a stipe,
leaflike structures called
blades, and
gas-filled bladders that
keep the alga afloat and
upright.
Blades
Bladder
Stipe
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Green Algae
Green Algae
Phylum Chlorophyta, “green plants.”
Share many characteristics with plants:
•Photosynthetic pigments: Chlorophyll a and b
•Cell wall composition: Cellulose
•Store food as starch
Scientists hypothesize that the ancestors of modern
land plants looked like certain species of living
green algae.
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Green Algae
Green algae live in fresh and salt water, and moist
land areas.
Many species live most of their lives as single cells.
Others form colonies, groups of similar cells that are
joined together but show few specialized structures.
A few are multicellular and have specialized
structures.
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Green Algae
Unicellular Green Algae
Chlamydomonas is a typical single-celled green alga
Grows in ponds, ditches, and wet soil
Egg shaped cell with two flagella and a single large
cup shaped chloroplast
Lacks large vacuoles, has two small contractile
vacuoles.
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Green Algae
Colonial Green Algae
Spirogyra forms long threadlike colonies called
filaments.
Volvox colonies are more elaborate, ranging from
500 to 50,000 cells arranged to form hollow spheres.
•Cells connected by strands of cytoplasm,
enabling coordinated movement.
•A few gamete producing cells are
specialized for reproduction.
•It straddles the fence between colonial and
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multicellular.
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Green Algae
Multicellular Green Algae
Ulva, “sea lettuce,” is a true multicellular organism.
The body is only two cells thick, but is tough enough
to survive pounding shoreline waves.
A group of cells at its base forms holdfasts that attach
to rocks.
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Reproduction in Green Algae
Reproduction in Green Algae
The life cycles of many algae include both a diploid
and a haploid generation.
Switching between haploid and diploid stages during
a life cycle is known as alternation of generations.
Many alga also shift between sexual and asexual
reproduction.
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Reproduction in Green Algae
Reproduction in Chlamydomonas
Release of haploid cells
zoospores
Zygote
Pairing of plus and
minus gametes
Mature cell
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Reproduction in Green Algae
zoospores
The unicellular
Chlamydomonas
spends most of its life
in the haploid stage.
In suitable living
conditions, this haploid
cell reproduces
asexually, producing
cells called zoospores
by mitosis.
Mature
cell
Mitosis
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Reproduction in Green Algae
If conditions become unfavorable, Chlamydomonas
can also reproduce sexually.
Release of haploid cells
Zygote
Pairing of plus and
minus gametes
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Haploid cells undergo
mitosis, but release
gametes instead of
zoospores.
Reproduction in Green Algae
Pairing of plus and
minus gametes
The gametes are of
two opposite mating
types—plus (+) and
minus (-).
The gametes gather
in large groups.
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Reproduction in Green Algae
The gametes form pairs, join flagella, shed their cell
walls and fuse, forming a diploid zygote.
The zygote sinks to the bottom of the pond and
grows a thick protective wall.
Within this protective wall, Chlamydomonas can
survive conditions that otherwise would kill it:
freezing, drying, etc.
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
When conditions again
become favorable, the
zygote grows, divides
by meiosis, and
produces four
flagellated haploid cells.
Reproduction in Green Algae
Release of
haploid cells
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Reproduction in Green Algae
Reproduction in Ulva
Ulva are gametophytes, or gamete-producing plants.
The haploid phase of Ulva produces male and female
gametes.
Fertilization
Gametes
Female
gametophyte
Mitosis
Male gametophyte
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Reproduction in Green Algae
When male and female gametes fuse, they produce
a diploid zygote cell, which grows into a diploid
multicellular Ulva.
Zygote
Sporophyte
Gametes
fuse
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Reproduction in Green Algae
The diploid Ulva undergoes meiosis to produce
haploid reproductive cells called spores.
MEIOSIS
Spores
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Reproduction in Green Algae
Each spore can
grow into a new
individual without
fusing with another
cell.
MEIOSIS
Because the diploid
Ulva produces
spores it is known
as a sporophyte,
or spore-producing
organism.
Spores
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Reproduction in Green Algae
Reproduction in Ulva
Meiosis
Mitosis
Gametes fuse
Zygote
Sporophyte
Spores
Fertilization
Gametes
Female
gametophyte
Mitosis
Male gametophyte
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20-4 Plantlike Protists: Red,
Brown, and Green Algae
Ecology of Algae
Ecology of Algae
Algae produce half of Earth’s oxygen through
photosynthesis and form the base of marine food
chains.
Algae is found in sushi, ice cream, salad dressing,
pudding, candy bars, pancake syrup, eggnog and
other foods.
Chemicals from algae are used to make plastics,
waxes, transistors, deodorants, paints, lubricants,
medicines, and artificial wood.
Agar thickens nutrient mixtures in scientific labs.
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