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Biology
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20-4 Plantlike Protists: Red, Brown, and Green Algae
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20-4 Plantlike Protists: Red, Brown, and Green Algae
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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
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20-4 Plantlike Protists: Red, Brown, and Green Algae
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Red Algae
Red Algae
What are the distinguishing features of red algae?
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20-4 Plantlike Protists: Red, Brown, and Green Algae
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Red Algae
Red algae are able to live at great depths due to their efficiency in harvesting light energy.
Red algae contain chlorophyll a and reddish accessory pigments called phycobilins.
Phycobilins absorb blue light, enabling red algae to live deep in the ocean.
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20-4 Plantlike Protists: Red, Brown, and Green Algae
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Brown Algae
Brown Algae
What are the distinguishing features of brown algae?
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20-4 Plantlike Protists: Red, Brown, and Green Algae
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Brown algae contain chlorophyll a and c, as well as a brown accessory pigment, fucoxanthin.
Brown Algae
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20-4 Plantlike Protists: Red, Brown, and Green Algae
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Brown Algae
Brown algae are the largest and most complex of the algae.
All are multicellular and 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
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Brown Algae
Brown Alga Structure
Blades
Bladder
Stipe
Holdfast
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20-4 Plantlike Protists: Red, Brown, and Green Algae
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Brown Algae
Fucus, a common brown alga, is made up of a holdfast, stipes, bladders, and blades.
The holdfast attaches the alga to rocks.
Holdfast
Blades
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20-4 Plantlike Protists: Red, Brown, and Green Algae
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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
Stipe
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20-4 Plantlike Protists: Red, Brown, and Green Algae
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Green Algae
Green Algae
What are the distinguishing features of green algae?
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20-4 Plantlike Protists: Red, Brown, and Green Algae
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Green Algae
Green algae share many characteristics with plants, including their photosynthetic pigments and cell wall composition.
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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Reproduction in Green Algae
Reproduction in Green Algae
How do multicellular algae reproduce?
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20-4 Plantlike Protists: Red, Brown, and Green Algae
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Reproduction in Green Algae
The life cycles of many algae include both a diploid and a haploid generation.
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20-4 Plantlike Protists: Red, Brown, and Green Algae
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Reproduction in Green Algae
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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Reproduction in Green Algae
Reproduction in Chlamydomonas
The unicellular Chlamydomonas spends most of its life in the haploid stage.
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Reproduction in Green Algae
Reproduction in Chlamydomonaszoospores
Mature cellPairing of plus andminus gametes
Zygote
Release of haploid cells
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Reproduction in Green Algae
Asexual Reproduction in Chlamydomonas
Mature cell
zoospores
In suitable living conditions, this haploid cell reproduces asexually, producing cells called zoospores by mitosis. Mitosis
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Reproduction in Green Algae
If conditions become unfavorable, Chlamydomonas can also reproduce sexually.
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20-4 Plantlike Protists: Red, Brown, and Green Algae
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Reproduction in Green Algae
Sexual Reproduction in Chlamydomonas
Release of haploid cells
Pairing of plus and minus gametes
Zygote
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Reproduction in Green Algae
Haploid cells undergo mitosis, but release gametes instead of zoospores.
The zoospores are of two opposite mating types—plus (+) and minus (-).
Pairing of plus and minus gametes
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Reproduction in Green Algae
The plus and minus gametes form pairs and fuse, forming a diploid zygote.
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Reproduction in Green Algae
The zygote grows a thick protective wall. Within this protective wall, Chlamydomonas can survive conditions that otherwise would kill it.
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Reproduction in Green Algae
When conditions again become favorable, the zygote grows, divides by meiosis, and produces four haploid cells.
Release of haploid cells
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Reproduction in Green Algae
Reproduction in Ulva
The life cycle of the green alga Ulva involves alternation of generations.
Ulva are gametophytes, or gamete-producing plants.
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Reproduction in Green Algae
Male gametophyte
Gametes
Female gametophyte
Gametes fuse Zygote Sporophyte
Spores
Mitosis Meiosis
Fertilization
Mitosis
Reproduction in Ulva
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Reproduction in Green Algae
The haploid phase of Ulva produces male and female gametes.
Gametes
Female gametophyte
Male gametophyte
Fertilization
Mitosis
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Reproduction in Green Algae
Gametes fuse
Zygote
Sporophyte
When male and female gametes fuse, they produce a diploid zygote cell, which grows into a diploid multicellular Ulva.
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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
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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
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20-4 Plantlike Protists: Red, Brown, and Green Algae
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Ecology of Algae
Ecology of Algae
Algae produce half of Earth’s oxygen through photosynthesis.
Algae is found in sushi, ice cream, and other foods.
Chemicals from algae are used to make plastics, waxes, transistors, deodorants, paints, lubricants, and artificial wood.
Agar thickens nutrient mixtures in scientific labs.
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20-4
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20-4
Reddish accessory pigments found in red algae are known as
a. chlorophyll a.
b. phycobilins.
c. fucoxanthins.
d. chlorophyll c.
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20-4
The giant kelp belongs to the group known as
a. green algae.
b. brown algae.
c. red algae.
d. golden algae.
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20-4
The life cycles of many algae include
a. haploid generations only.
b. diploid generations only.
c. both haploid and diploid generations.
d. only asexual reproduction.
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20-4
The green alga Chlamydomonas reproduces asexually by producing
a. zygotes.
b. gametes.
c. zoospores.
d. holdfasts.
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20-4
Cells that can grow into new organisms without fusing with another cell are called
a. gametes.
b. spores.
c. gametophytes.
d. sporophytes.
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