20-3 Plantlike Protists:
Unicellular Algae
Slide
1 of 33
Copyright Pearson Prentice Hall
End Show
20-3 Plantlike Protists:
Unicellular Algae
Plantlike Protists
Plantlike protists contain chlorophyll and carry out
photosynthesis.
Plantlike protists are commonly called “algae.”
Algae are sometimes classified with the plants.
There are seven major phyla: three multicellular and
four unicellular.
Slide
2 of 33
Copyright Pearson Prentice Hall
End Show
20-3 Plantlike Protists:
Unicellular Algae
Plantlike Protists
The four phyla of unicellular algae are:
• Euglenophyta
• Chrysophyta
• Bacillariophyta
• Pyrrophyta
Slide
3 of 33
Copyright Pearson Prentice Hall
End Show
20-3 Plantlike Protists:
Unicellular Algae
Chlorophyll and Accessory
Pigments
Chlorophyll and Accessory Pigments
Allow algae to harvest and use energy from sunlight.
Life in water poses a problem for photosynthesis.
Much of light’s energy is absorbed by water.
Seawater absorbs large amounts of red and violet
wavelengths, so light becomes dimmer and bluer in
deeper waters.
Chlorophyll a is most efficient at capturing red and
violet light, so in deep waters it is ineffective for
photosynthesis.
Copyright Pearson Prentice Hall
Slide
4 of 33
End Show
20-3 Plantlike Protists:
Unicellular Algae
Chlorophyll and Accessory
Pigments
One trait used to classify algae is the type of
photosynthetic pigments they contain.
Some algae have evolved different forms of
chlorophyll—a, b, and c—that absorb different
wavelengths of light to adapt to the condition of their
watery environment.
Accessory pigments absorb light at different
wavelengths than chlorophyll, giving algae a variety of
colors.
Accessory pigments pass the energy they absorb to
the photosynthetic machinery of the algae.
Slide
5 of 33
Copyright Pearson Prentice Hall
End Show
20-3 Plantlike Protists:
Unicellular Algae
Euglenophytes
Phylum Euglenophyta: Euglenophytes
Euglenophytes are plantlike protists that have two
flagella but no cell wall.
They are closely related to the zooflagellates.
The phylum is named for the genus Euglena, which
contains organisms found in ponds and lakes
worldwide.
A typical euglena is about 50 micrometers long, and
an excellent swimmer.
Slide
6 of 33
Copyright Pearson Prentice Hall
End Show
20-3 Plantlike Protists:
Unicellular Algae
Euglenophytes
Pellicle
Euglena
Carbohydrate
storage bodies
Contractile vacuole
Chloroplast
Nucleus
Eyespot
Gullet
Flagella
Slide
7 of 33
Copyright Pearson Prentice Hall
End Show
20-3 Plantlike Protists:
Unicellular Algae
Euglenophytes
Two flagella emerge from
a gullet in the cell.
The longer of the flagella
spins so it pulls the
organism rapidly through
the water.
Gullet
Flagella
Slide
8 of 33
Copyright Pearson Prentice Hall
End Show
20-3 Plantlike Protists:
Unicellular Algae
Euglenophytes
Near the gullet is a
reddish pigment known
as the eyespot, which
helps find sunlight to
power photosynthesis.
Euglenas can also live as
heterotrophs, absorbing
nutrients from decayed
organic matter.
Eyespot
Slide
9 of 33
Copyright Pearson Prentice Hall
End Show
20-3 Plantlike Protists:
Unicellular Algae
Euglenophytes
Euglenas store
carbohydrates in small
storage bodies.
Carbohydrate
storage bodies
Euglenas reproduce
asexually by binary
fission.
Slide
10 of 33
Copyright Pearson Prentice Hall
End Show
20-3 Plantlike Protists:
Unicellular Algae
Euglenophytes
Euglenas do not have cell
walls. Instead, they have an
intricate cell membrane
called a pellicle.
Pellicle
The pellicle folds into ridges,
each supported by
microtubules.
It is tough and flexible,
allowing euglenas to crawl
through mud when there isn’t
enough water.
Copyright Pearson Prentice Hall
Slide
11 of 33
End Show
20-3 Plantlike Protists:
Unicellular Algae
Chrysophytes
Chrysophytes
Members of the phylum Chrysophyta are a diverse
group of plantlike protists including yellow-green
algae and golden-brown algae.
Their chloroplasts contain bright yellow pigments that
give the phylum its name.
Chrysophyta means “golden plants.”
Slide
12 of 33
Copyright Pearson Prentice Hall
End Show
20-3 Plantlike Protists:
Unicellular Algae
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.
Slide
13 of 33
Copyright Pearson Prentice Hall
End Show
20-3 Plantlike Protists:
Unicellular Algae
Diatoms
Diatoms
Members of the phylum Bacillariophyta.
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.
Slide
14 of 33
Copyright Pearson Prentice Hall
End Show
20-3 Plantlike Protists:
Unicellular Algae
Dinoflagellates
Dinoflagellates
Members of the phylum Pyrrophyta.
About half of the dinoflagellates are photosynthetic;
the other half live as heterotrophs.
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.
Slide
15 of 33
Copyright Pearson Prentice Hall
End Show
20-3 Plantlike Protists:
Unicellular Algae
Dinoflagellates
Many dinoflagellates are luminescent.
When they are agitated, they give off light.
Some areas of the ocean ate so filled with
dinoflagellates that the movement of a boat’s hull
will cause the dark water to shimmer with blue light.
This luminescence gives the phylum its name:
Pyrrophyta, meaning “fire plants.”
Slide
16 of 33
Copyright Pearson Prentice Hall
End Show
20-3 Plantlike Protists:
Unicellular Algae
Ecology of Unicellular Algae
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.
They make up a considerable portion of phytoplankton
found in marine ecosystems.
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
Slide
organisms.
17 of 33
Copyright Pearson Prentice Hall
End Show
20-3 Plantlike Protists:
Unicellular Algae
Ecology of Unicellular Algae
Algal Blooms
Many protists are vital in recycling sewage and
other wastes.
When waste is excessive, algae may grow into
enormous masses known as blooms, which
deplete water of nutrients and the cells die in great
numbers.
Their decomposition robs water of oxygen, killing
fish and invertebrate life and disrupting the
equilibrium of the aquatic ecosystem.
Copyright Pearson Prentice Hall
Slide
18 of 33
End Show
20-3 Plantlike Protists:
Unicellular Algae
Red Tides
Red Tide
Great blooms of certain dinoflagellates have occurred
in recent years on the east coast for unknown reasons.
These blooms are known as “red tides.”
These species produce a potentially dangerous toxin,
and when filter-feeding shellfish eat the dinoflagellates
they become filled with toxin.
Eating shellfish infected by red tides can cause serious
illness, paralysis, and even death in humans and fish.
Slide
19 of 33
Copyright Pearson Prentice Hall
End Show