1. 20-4 Plantlike Protists: Red, Brown, and Green Algae
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2. 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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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 reddish- black.
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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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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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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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Brown Algae
Fucus, a common brown alga also known as rock weed, is made up of a holdfast, stipes, bladders, and blades.
The holdfast attaches the alga to rocks.
Blades
Brown algae contain chlorophyll a and c, plus fucoxanthin, a brown pigment.
Holdfast
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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
Brown algae contain chlorophyll a and c, plus fucoxanthin, a brown pigment.
Stipe
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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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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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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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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 multicellular.
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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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14. 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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15. Reproduction in Green Algae
Reproduction in Chlamydomonas
zoospores
Release of haploid cells
Zygote
Pairing of plus and minus gametes
Mature cell
The green alga Chlamydomonas reproduces asexually by producing zoospores and sexually by producing zygotes, which release haploid gametes.
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16. 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
The green alga Chlamydomonas reproduces asexually by producing zoospores and sexually by producing zygotes, which release haploid gametes.
Mitosis
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17. Reproduction in Green Algae
If conditions become unfavorable, Chlamydomonas can also reproduce sexually.
Release of haploid cells
Zygote
Pairing of plus and
minus gametes
The green alga Chlamydomonas reproduces asexually by producing zoospores and sexually by producing zygotes, which release haploid gametes.
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18. Reproduction in Green Algae
Haploid cells undergo mitosis, but release gametes instead of zoospores.
The gametes are of two opposite mating types—plus (+) and minus (-).
The gametes gather in large groups.
Pairing of plus and minus gametes
The green alga Chlamydomonas reproduces sexually by producing zygotes, which release haploid gametes.
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19. 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.
The green alga Chlamydomonas reproduces sexually by producing zygotes, which release haploid gametes.
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20. Reproduction in Green Algae
Release of haploid cells
When conditions again become favorable, the zygote grows, divides by meiosis, and produces four flagellated haploid cells.
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21. 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
The life cycles of most algae include both diploid and haploid generations. The multicellular green alga Ulva exhibits alternation of generations. The haploid generation produces a diploid generation. Then, the diploid generation produces a haploid generation. The two generations are multicellular and virtually indistinguishable from each other.
Male gametophyte
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22. Reproduction in Green Algae
When male and female gametes fuse, they produce a diploid zygote cell, which grows into a diploid multicellular Ulva.
The life cycles of most algae include both diploid and haploid generations. The multicellular green alga Ulva exhibits alternation of generations. The haploid generation produces a diploid generation. Then, the diploid generation produces a haploid generation. The two generations are multicellular and virtually indistinguishable from each other.
Zygote
Sporophyte
Gametes fuse
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23. Reproduction in Green Algae
The diploid Ulva undergoes meiosis to produce haploid reproductive cells called spores.
MEIOSIS
The life cycles of most algae include both diploid and haploid generations. The multicellular green alga Ulva exhibits alternation of generations. The haploid generation produces a diploid generation. Then, the diploid generation produces a haploid generation. The two generations are multicellular and virtually indistinguishable from each other.
Spores
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24. Reproduction in Green Algae
Each spore can grow into a new individual without fusing with another cell.
Because the diploid Ulva produces spores it is known as a sporophyte, or spore-producing organism.
MEIOSIS
Spores
The life cycles of most algae include both diploid and haploid generations. The multicellular green alga Ulva exhibits alternation of generations. The haploid generation produces a diploid generation. Then, the diploid generation produces a haploid generation. The two generations are multicellular and virtually indistinguishable from each other.
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25. Reproduction in Green Algae
Reproduction in Ulva
Mitosis
Meiosis
Gametes fuse
Zygote
Sporophyte
Spores
Fertilization
Gametes
The life cycles of most algae include both diploid and haploid generations. The multicellular green alga Ulva exhibits alternation of generations. The haploid generation produces a diploid generation. Then, the diploid generation produces a haploid generation. The two generations are multicellular and virtually indistinguishable from each other.
Mitosis
Female
gametophyte
Male gametophyte
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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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