1. Protists

2. Chapter 27 Opening Roadmap.
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3. Protists All eukaryotes except land plants, fungi, and animals
Figure 27.1
Protists
All eukaryotes except land plants, fungi, and animals
Tend to live in environments where they are surrounded by water most of the time
Open ocean: Surface waters
teem with microscopic protists,
such as these diatoms.
Shallow coastal waters:
Gigantic protists, such as
these kelp, form underwater
forests.
Intertidal habitats: Protists
such as these brown algae are
particularly abundant in tidal
habitats.
Figure 27.1 Protists Are Particularly Abundant in Aquatic Environments.
1 mm
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4. Impacts on Human Health and Welfare
Several types of protists can cause human disease, and some also cause disease in our crops
Irish potato famine of 1845: caused by the protist Phytophthora infestans
Type of water mold
Led to emigration, and mass starvation caused deaths

5. Malaria is one of the world’s most chronic public health problems
Figure 27.2
Malaria is one of the world’s most chronic public health problems
Five species of the parasitic protist Plasmodium transferred to humans from mosquitoes
Haploid (n)
Plasmodium
cell type
present in
mosquito
saliva that
infects
humans
MITOSIS
MITOSIS
Diploid (2n)
Mosquito
bite
(n)
(n)
Infection of liver
cells in human
Human host
Figure 27.2 Plasmodium Lives in Mosquitoes and in Humans, Where It Causes Malaria.
Mosquito host
Infec
tion o
f gut w
all in m o
Male
gametes (n)
squito
Plasmodium
cell types
present in
human blood
that infect
mosquitoes
MEIOSIS
followed by
MITOSIS
Mosquito
bite
Zygote
SYNGAMY
(2n)
Female
gamete (n)
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6. Table 27.1 Some Human Health Problems Caused by Protists.
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7. Red tide: caused by photosynthetic dinoflagellates
Figure 27.3
Shellfish filter-feed these organisms out of the water and are not harmed.
Toxins accumulating in the shellfish poison animals including humans.
20 µm
Figure 27.3 Harmful Algal Blooms Caused by Dinoflagellates.
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8. CO2 Photosynthetic protists fix carbon from the atmosphere.
Figure 27.4
CO2
Arrows indicate movement
of carbon atoms
Photosynthetic protists fix carbon from the atmosphere.
Heterotrophic protists consume producers.
All protists eventually die.
Decomposers return carbon.
But dead cells accumulate as a carbon reserve: limestone and/or fossil fuels.
Primary producers
Primary consumers
Figure 27.4 Protists Play a Key Role in the Marine Carbon Cycle.
Decomposers and scavengers
Sinking
Sinking
Sinking
Dead cells and CaCO3 shells accumulate on bottom
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9. Flagellum Hairs on flagellum Branches on hairs 1 µm Table 27.2
Table 27.2 Distinguishing Features (Synapomorphies) of Major Lineages of Eukaryotes.
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10. Most are unicellular, most are aquatic.
Figure 27.6
Protista, a kingdom, was established in the 1900s – to contain organisms difficult to place.
Most are unicellular, most are aquatic.
Can be thought of as polyphyletic, or as monophyletic with nested kingdoms.
Bacteria
The Amoebozoa and Opisthokonta form the monophyletic group Unikonta (one tailed)
Archaea
AMOEBOZOA
Lobose amoebae
Cellular slime molds
UNIKONTA
Plasmodial slime molds
OPISTHOKONTA
Fungi
Choanoflagellates
All eukaryotes
are protists
except for the
fungi, animals,
and land plants
Animals
EXCAVATA
Parabasalids
EUKARYOTES
Diplomonads
Euglenids
Kinetoplastids
PLANTAE
The other five major lineages form the monophyletic group Bikonta (two tailed)
Glaucophyte algae
Red algae
Green algae
Green
plants
Land plants
BIKONTA
Figure 27.6 Phylogenetic Analyses Have Identified Seven Major Lineages of Eukaryotes.
RHIZARIA
Actinopods
Foraminiferans
Chlorarachniophytes
ALVEOLATA
Ciliates
Dinoflagellates
Apicomplexans
STRAMENOPILA
Water molds
Diatoms
Brown algae
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11. Related to muscle movement in animals
Figure 27.14
Amoeboid motion is a sliding movement observed in some protists that is accomplished by streaming of pseudopodia
Amoeboid motion via pseudopodia
Chaos carolinensis
Figure Amoeboid Motion Is Possible in Species That Lack Cell Walls.
0.2 mm
Requires ATP
Related to muscle movement in animals
Key immune system cells in humans use amoeboid motion
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12. Flagella and cilia have identical structures, however:
Figure 27.15
Flagella and cilia have identical structures, however:
Flagella are long and are usually found alone or in pairs
Cilia are short and numerous
(a) Swimming via flagella
(b) Swimming via cilia
Figure Many Protists Swim Using Flagella or Cilia.
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13. Protists evolved the complementary processes:
Figure 27.16a
Protists evolved the complementary processes:
mitosis, meiosis, and syngamy in their life cycles
(a) A life cycle dominated by haploid cells (species shown here is the dinoflagellate
Gyrodinium uncatenum)
Haploid (n)
Diploid (2n)
SYNGAMY
(n)
Zygote
(2n)
Sexual reproduction
(offspring produced
by meiosis)
Asexual reproduction
(offspring produced
by mitosis)
Flagella
10 µm
Fusing gamete
pair
Mature cell
Figure 27.16a Life Cycles Vary Widely among Unicellular Protists.
(n)
(n)
Gamete
Gametes
(n)
(n)
This is a unicellular life cycle which is dominated by populations of haploid cells with asexual reproduction
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14. Other protists evolved the life cycle differently:
Figure 27.16b
Other protists evolved the life cycle differently:
(b) A life cycle dominated by diploid cells (species shown here is the diatom
Thalassiosira punctigera)
In each division both
halves become the external
template of the daughter
cells, therefore one of the
daughter cells will be smaller
Haploid (n)
Diploid (2n)
Zygote
(2n)
Initial cell
Asexual reproduction
(offspring produced
by mitosis)
Sexual reproduction
(offspring produced
by meiosis)
60 µm
Mature cell
(2n)
Figure 27.16b Life Cycles Vary Widely among Unicellular Protists.
Silicon dioxide
cell wall
Sperm
MEIOSIS
SYNGAMY
(2n)
Nucleus
The smaller cells
cannot divide any more
and undergo sexual
reproduction
20 µm
Egg
MEIOSIS
Gametes
(n)
This is a unicellular life cycle which is dominated by populations of diploid cells with asexual reproduction
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15. Figure 27.17a
Yet other protists evolved with multicellular stages in their life cycles
(a) Alternation of generations in which multicellular haploid and diploid forms look
identical (Ectocarpus siliculosus)
Male and female
gametophytes
are separate
Meiosis occurs in
specialized structures
Spores (n)
100 µm
Gametes are
produced by
mitosis in
specialized
structures
Gametophytes
1 cm
(n)
Figure 27.17a Alternation of Generations Occurs in Many Multicellular Protists.
Gametes
Sporophyte
(n)
(2n)
Egg
Sperm
Haploid (n)
50 µm
Diploid (2n)
SYNGAMY
Zygote germinates and
grows into sporophyte
Zygote
(2n)
This is a diplohaplontic life cycle with multicellular diploid (sporophyte) and multicellular haploid (gametophyte) stages.
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16. Table 27.3-1 Key Lineages of Protists.
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17. Table 27.3-2 Key Lineages of Protists.
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