20-3 Plantlike Protists: Unicellular...

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Copyright Pearson Prentice Hall

20-3 Plantlike Protists:

Unicellular Algae


Unicellular Algae

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Plantlike protists contain chlorophyll and carry out

photosynthesis.

Plantlike protists are commonly called “algae.”

Algae are sometimes classified with the plants.


Unicellular Algae

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The four phyla of unicellular algae are:

• euglenophytes

• chrysophytes

• diatoms

• dinoflagellates


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Chlorophyll and Accessory

Pigments

Chlorophyll and accessory pigments allow

algae to harvest and use the energy from

sunlight.


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One trait used to classify algae is the type of photosynthetic pigments they contain.

Some algae have different forms of chlorophyll—a, b, and c—that absorb different wavelengths of light.

Accessory pigments absorb light at different wavelengths than chlorophyll, giving algae a variety of colors.

Chlorophyll and Accessory

Pigments


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Euglenophytes

Euglenophytes are plantlike protists that

have two flagella but no cell wall.


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Euglena

Euglenophytes

Gullet

Flagella

Eyespot

Pellicle

Contractile vacuole Carbohydrate

storage bodies

Chloroplast

Nucleus


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Two flagella emerge from

a gullet in the cell. The

longer of the flagella

spins so it pulls the

organism rapidly through

the water.

Euglenophytes

Gullet

Flagella


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Near the gullet is a

reddish pigment known

as the eyespot, which

helps find sunlight to

power photosynthesis.

Euglenas can also live as

heterotrophs.

Euglenophytes

Eyespot


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Euglenas store

carbohydrates in small

storage bodies.

Euglenophytes

Carbohydrate

storage bodies


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Euglenas do not have

cell walls. Instead, they

have an intricate cell

membrane called a

pellicle.

The pellicle folds into

ridges, each supported

by microtubules.

Euglenas reproduce

asexually by binary

fission.

Euglenophytes

Pellicle


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Chrysophytes

Members of the phylum Chrysophyta

are a diverse group of plantlike protists

that have gold-colored chloroplasts.


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Chrysophytes

The cell walls of some chrysophytes contain the

carbohydrate pectin rather than cellulose, and others

contain both.

Chrysophytes store food in the form of oil rather than

starch.

They reproduce both asexually and sexually.

Most are solitary, but some form threadlike colonies.


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Diatoms

Diatoms produce thin, delicate cell walls

rich in silicon (Si)—the main component of

glass.

The walls are shaped like the two sides of a

petri dish or flat pillbox, with one side fitted

snugly into the other.


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Dinoflagellates

Dinoflagellates

About half of the dinoflagellates are

photosynthetic; the other half live as

heterotrophs.


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Dinoflagellates

Dinoflagellates have two flagella that fit in grooves

between two thick plates of cellulose that protect the

cell.

Most dinoflagellates reproduce asexually by binary

fission.

Many dinoflagellates are luminescent. When they are

agitated, they give off light.


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Ecology of Unicellular Algae


Plantlike protists are important to freshwater and

marine ecosystems because they make up the

base of the food chain in many aquatic

ecosystems.


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Phytoplankton constitute the population of small,

photosynthetic organisms found near the surface of

the ocean.

Phytoplankton carry out half of Earth’s

photosynthesis. In addition, they provide nourishment

for many organisms.


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20-4 Plantlike Protists: Red,

Brown, and Green Algae


Unicellular 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


Unicellular 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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Brown algae contain chlorophyll a and c, as well as a brown accessory pigment, fucoxanthin.

Brown 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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Brown Algae

Brown Alga Structure

Blades

Bladder

Stipe

Holdfast


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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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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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Green Algae

Green algae share many characteristics with plants, including their photosynthetic pigments and cell wall composition.


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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

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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Reproduction in Chlamydomonas

• The unicellular Chlamydomonas spends most of

its life in the haploid stage.


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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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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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