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Biology in Focus - Chapter 25

- Eukaryotes originated over 1.8 billion years ago through endosymbiosis, where ancient prokaryotes lived inside early cells. - The earliest fossils of eukaryotic cells date back 1.8 billion years, and initial diversification of eukaryotes occurred between 1.8-1.3 billion years ago. - Novel features in eukaryotes like complex multicellularity, sexual reproduction and photosynthesis arose between 1.3-635 million years ago.

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CAMPBELL BIOLOGY IN FOCUS © 2014 Pearson Education, Inc. Urry • Cain • Wasserman • Minorsky • Jackson • Reece Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge 25 The Origin and Diversification of Eukaryotes
Overview: Shape Changers  Protist is the informal name of the diverse group of mostly unicellular eukaryotes  Some protists, like the ciliate Didinium, are able to perform dramatic shape changes due to the structural complexity of their cells © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.1
Concept 25.1: Eukaryotes arose by endosymbiosis more than 1.8 billion years ago  Early eukaryotes were unicellular  Eukaryotic cells have organelles and are structurally more complex than prokaryotic cells  A well-developed cytoskeleton enables eukaryotic cells to have asymmetrical forms and to change shape © 2014 Pearson Education, Inc.
The Fossil Record of Early Eukaryotes  Chemical evidence for the presence of eukaryotes dates back to 2.7 billion years ago  The earliest fossils of eukaryotic cells are 1.8 billion years old © 2014 Pearson Education, Inc.
 Initial diversification of eukaryotes occurred 1.8 to 1.3 billion years ago  Novel features of eukaryotes, including complex multicellularity, sexual life cycles, and photosynthesis, arose 1.3 billion to 635 million years ago  The first large, multicellular eukaryotes represented by the Ediacaran biota evolved 635 to 535 million years ago © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.2 4.5 bya 3.5 1.52.5 500 mya 1.8 bya 1.5 bya 1.3 bya 1.2 bya 20 µm 20µm 25 µm 25 µm (a) A 1.8-billion- year-old fossil eukaryote (b) Tappania, a 1.5-billion-year-old fossil that may represent an early alga or fungus (c) Bangiomorpha, an ancient red alga 20µm (d) Proterocladus, classified as a green alga (e) Bonneia, a vase-shaped eukaryote (f) An early member of the Ediacaran biota (g) Spriggina floundersi, an early animal with many body segments 750 mya 635 mya 600 mya 550 mya 535 mya 1 cm 0.5 cm
© 2014 Pearson Education, Inc. Figure 25.2a 4.5 bya 3.5 1.52.5 500 mya 1.8 bya 1.5 bya 20 µm 20µm (a) A 1.8-billion- year-old fossil eukaryote (b) Tappania, a 1.5-billion-year-old fossil that may represent an early alga or fungus Initial diversification
© 2014 Pearson Education, Inc. Figure 25.2aa 20 µm (a) A 1.8-billion-year-old fossil eukaryote
© 2014 Pearson Education, Inc. Figure 25.2ab (b) Tappania, a 1.5-billion-year-old fossil that may represent an early alga or fungus 20µm
© 2014 Pearson Education, Inc. Figure 25.2b 4.5 bya 3.5 1.52.5 500 mya Appearance of novel features 1.3 bya 1.2 bya 750 mya 20µm 25 µm 25 µm (c) Bangiomorpha, an ancient red alga (d) Proterocladus, classified as a green alga (e) Bonneia, a vase-shaped eukaryote
© 2014 Pearson Education, Inc. Figure 25.2ba 25 µm (c) Bangiomorpha, an ancient red alga
© 2014 Pearson Education, Inc. Figure 25.2bb 25 µm (d) Proterocladus, classified as a green alga
© 2014 Pearson Education, Inc. Figure 25.2bc 20µm (e) Bonneia, a vase-shaped eukaryote
© 2014 Pearson Education, Inc. Figure 25.2c 4.5 bya 3.5 1.52.5 500 mya Rise of large eukaryotes 635 mya 600 mya 550 mya 535 mya 1 cm 0.5 cm (f) An early member of the Ediacaran biota (g) Spriggina floundersi, an early animal with many body segments
© 2014 Pearson Education, Inc. Figure 25.2ca 1 cm (f) An early member of the Ediacaran biota
© 2014 Pearson Education, Inc. Figure 25.2cb 0.5 cm (g) Spriggina floundersi, an early animal with many body segments
 Eukaryotic cells exhibited greater structural complexity than prokaryotic cells as early as 1.5 billion years ago  The earliest multicellular eukaryotic fossils are of red algae, which date back to 1.2 billion years ago, but large, multicellular eukaryotes did not arise until 635 million years ago  Severe ice ages from 750 to 580 million years ago may have hindered the rise of large eukaryotes © 2014 Pearson Education, Inc.
Endosymbiosis in Eukaryotic Evolution  DNA sequence data indicate that eukaryotes are “combination” organisms  Eukaryotic genes and characteristics show evidence of both archaeal and bacterial origins  Evidence of mixed origins may be a consequence of endosymbiosis, a symbiotic relationship in which one organism lives inside the body or cell of another organism © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Table 25.1
Origin of Mitochondria and Plastids  Endosymbiont theory proposes that mitochondria and plastids were formerly small prokaryotes that began living within larger cells  An endosymbiont is a cell that lives within a host cell  Prokaryote ancestors to mitochondria and plastids probably entered the host cell as undigested prey or internal parasites © 2014 Pearson Education, Inc.
 The relationship between endosymbiont and host cells was mutually beneficial  Anaerobic host cells benefited from endosymbionts’ ability to take advantage of an increasingly aerobic world  Heterotrophic host cells benefited from the nutrients produced by photosynthetic endosymbionts  In the process of becoming more interdependent, the host and endosymbionts would have become a single organism © 2014 Pearson Education, Inc.
 Serial endosymbiosis supposes that mitochondria evolved before plastids through a sequence of endosymbiotic events © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.3 Cytoplasm DNA Nucleus Engulfing of aerobic bacterium Engulfing of photo- synthetic bacterium Mitochondrion Mito- chondrion Plastid Plasma membrane Endoplasmic reticulum Nuclear envelope Ancestral prokaryote Ancestral heterotrophic eukaryote Ancestral photosynthetic eukaryote
 Key evidence supporting an endosymbiotic origin of mitochondria and plastids:  Inner membranes are similar to plasma membranes of prokaryotes  Division is similar in these organelles and some prokaryotes  DNA structure is similar to that of prokaryotes  These organelles transcribe and translate their own DNA  Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes © 2014 Pearson Education, Inc.
 DNA sequence analysis indicates that mitochondria arose from an alpha proteobacterium  Eukaryotic mitochondria descended from a single common ancestor  Plastids arose from an engulfed cyanobacterium  Some photosynthetic protists may have been engulfed to become endosymbionts themselves © 2014 Pearson Education, Inc.
 The ancestral host cell may have been an archaean or a “protoeukaryote,” from a lineage related to, but diverged from, archaeal ancestors © 2014 Pearson Education, Inc.
Plastid Evolution: A Closer Look  There is now considerable evidence that much protist diversity has its origins in endosymbiosis  Mitochondria arose first through descent from a bacterium that was engulfed by a cell from an archaeal lineage  The plastid lineage evolved later from a photosynthetic cyanobacterium that was engulfed by a heterotrophic eukaryote © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.4 Cyano- bacterium Membranes are represented as dark lines in the cell. Red alga Primary endo- symbiosis 1 2 3 Nucleus Heterotrophic eukaryote One of these membranes was lost in red and green algal descendants. Green alga Secondary endo- symbiosis Secondary endo- symbiosis Plastid Euglenids Chlorarachniophytes Stramenopiles Plastid Secondary endo- symbiosis Dinoflagellates
© 2014 Pearson Education, Inc. Figure 25.4a Cyano- bacterium Membranes are represented as dark lines in the cell. Red alga Primary endosymbiosis 1 2 3 Nucleus Heterotrophic eukaryote One of these membranes was lost in red and green algal descendants. Green alga
© 2014 Pearson Education, Inc. Figure 25.4b Secondary endosymbiosis Red alga Plastid Dinoflagellates Stramenopiles
© 2014 Pearson Education, Inc. Figure 25.4c Secondary endosymbiosis Plastid Euglenids Green alga Chlorarachniophytes
 The plastid-bearing lineage of protists evolved into red and green algae  Like cyanobacteria, plastids of red algae and green algae have two membranes  Transport proteins in the membranes of red and green algae are homologous to those found in cyanobacteria  On several occasions during eukaryotic evolution, red and green algae underwent secondary endosymbiosis, in which they were ingested by a heterotrophic eukaryote © 2014 Pearson Education, Inc.
Concept 25.2: Multicellularity has originated several times in eukaryotes  The evolution of eukaryotic cells allowed for a greater range of unicellular forms  A second wave of diversification occurred when multicellularity evolved and gave rise to algae, plants, fungi, and animals © 2014 Pearson Education, Inc.
Multicellular Colonies  The first multicellular forms were colonies, collections of cells that are connected to one another but show little or no cellular differentiation  Multicellular colonies consist of simple filaments, balls, or cell sheets  Colonial cells may be attached by shared cell walls or, in cells that lack rigid walls, held together by proteins that physically connect adjacent cells © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.5 Pediastrum
Independent Origins of Complex Multicellularity  Multicellular organisms with differentiated cells originated multiple times over the course of eukaryotic evolution  Genetic and morphological evidence indicates that lineages of red, green, and brown algae, plants, fungi, and animals arose independently from different single-celled ancestors © 2014 Pearson Education, Inc.
 Volvox is a multicellular green algae that forms a monophyletic group with a single-celled alga (Chlamydomonas) and several colonial species  Volvox and all colonial members of this group have proteins homologous to those found in the cell wall of Chlamydomonas  Multicellularity in Volvox may have originated through evolution of increasingly complex colonial forms descended from a single-celled common ancestor © 2014 Pearson Education, Inc. Video: Chlamydomonas
© 2014 Pearson Education, Inc. Figure 25.6 Flagellum Cytoplasm Outer cell wall Inner cell wall Outer cell wall Cytoplasm Extracellular matrix (ECM) Chlamydomonas Gonium Pandorina Volvox
 Only a few novel genes account for morphological differences between Volvox and Chlamydomonas  The transition to multicellularity may result from changes in how existing genes are used rather than the origin of large numbers of novel genes © 2014 Pearson Education, Inc.
Steps in the Origin of Multicellular Animals  Choanoflagellates are the closest living relatives of animals  The common ancestor of choanoflagellates and living animals may have resembled present-day choanoflagellates © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.7 Individual choanoflagellate Choano- flagellates Other animals Collar cell (choanocyte) Sponges Animals OTHER EUKARY- OTES
 The origin of multicellularity in animals required mechanisms for cells to adhere to each other and to communicate with each other (cell signaling)  Molecular similarities in domains of proteins functioning in cell adherence (cadherins) and cell signaling have been found between modern choanoflagellates and representative animals © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.8 Hydra Mouse “CCD” domain Choano- flagellate Fruit fly
 The transition to multicellularity in animals involved new ways of using proteins encoded by genes found in choanoflagellates rather than the evolution of many novel genes © 2014 Pearson Education, Inc.
Concept 25.3: Four “supergroups” of eukaryotes have been proposed based on morphological and molecular data  Eukaryote diversity is influenced by their hybrid origins and the independent origins of complex multicellularity  One hypothesis divides all eukaryotes into four supergroups © 2014 Pearson Education, Inc.
Four Supergroups of Eukaryotes  It is no longer thought that amitochondriates (lacking mitochondria) are the oldest lineage of eukaryotes  Many have been shown to have mitochondria and have been reclassified  Our understanding of the relationships among protist groups continues to change rapidly  One hypothesis divides all eukaryotes (including protists) into four supergroups © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Video: Amoeba Pseudopodia Video: Volvox Colony Video: Amoeba Video: Volvox Female Spheroid Video: Volvox Flagella Video: Volvox Daughter Video: Volvox Inversion 1 Video: Volvox Sperm Video: Volvox Inversion 2
© 2014 Pearson Education, Inc. Figure 25.9 Stramen- opiles Diplomonads Parabasalids Euglenozoans Excavata Alveo- lates Rhiza- rians Diatoms Brown algae Dinoflagellates Apicomplexans Ciliates Forams Cercozoans “SAR”clade Green algae Amoebo- zoans Red algae Chlorophytes Charophytes Land plants Archaeplastida Opisthokonts Unikonta Gymnamoebas Slime molds Nucleariids Fungi Choanoflagellates Animals 100 µm 50 µm “SAR” Clade Excavata 5 µm Archaeplastida 20 µm 50 µm Unikonta 100 µm
© 2014 Pearson Education, Inc. Figure 25.9a Stramen- opiles Diplomonads Parabasalids Euglenozoans Excavata Alveo- lates Rhiza- rians Diatoms Brown algae Dinoflagellates Apicomplexans Ciliates Forams Cercozoans “SAR”clade Green algae Amoebo- zoans Red algae Chlorophytes Charophytes Land plants Archaeplastida Opisthokonts Unikonta Gymnamoebas Slime molds Nucleariids Fungi Choanoflagellates Animals
© 2014 Pearson Education, Inc. Figure 25.9aa Stramen- opiles Diplomonads Parabasalids Euglenozoans Excavata Alveo- lates Rhiza- rians Diatoms Brown algae Dinoflagellates Apicomplexans Ciliates Forams Cercozoans “SAR”clade
© 2014 Pearson Education, Inc. Figure 25.9ab Green algae Amoebo- zoans Red algae Chlorophytes Charophytes Land plants Archaeplastida Opisthokonts Unikonta Gymnamoebas Slime molds Nucleariids Fungi Choanoflagellates Animals
© 2014 Pearson Education, Inc. Figure 25.9b Excavata “SAR” Clade Archaeplastida 50 µm 50 µm 20 µm 5 µm Unikonta 100 µm 100 µm
© 2014 Pearson Education, Inc. Figure 25.9ba Giardia intestinalis, a diplomonad parasite 5 µm
© 2014 Pearson Education, Inc. Figure 25.9bb Diatom diversity 50 µm
© 2014 Pearson Education, Inc. Figure 25.9bc Globigerina, a rhizarian in the SAR supergroup 100 µm
© 2014 Pearson Education, Inc. Figure 25.9bca Globigerina, a rhizarian in the SAR supergroup 100 µm
© 2014 Pearson Education, Inc. Figure 25.9bcb
© 2014 Pearson Education, Inc. Figure 25.9bd Volvox, a multicellular freshwater green alga 20 µm 50 µm
© 2014 Pearson Education, Inc. Figure 25.9bda Volvox, a multicellular freshwater green alga 50 µm
© 2014 Pearson Education, Inc. Figure 25.9bdb 20 µm
© 2014 Pearson Education, Inc. Figure 25.9be 100 µm A unikont amoeba
Excavates  The supergroup Excavata is characterized by its cytoskeleton  Some members have a feeding groove  This monophyletic group includes the diplomonads, parabasalids, and euglenozoans © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.UN02 Diplomonads Parabasalids Euglenozoans Excavata SAR clade Archaeplastida Unikonta
Diplomonads and Parabasalids  These two groups lack plastids and have modified mitochondria, and most live in anaerobic environments  Diplomonads  Have reduced mitochondria called mitosomes  Derive energy from anaerobic biochemical pathways  Are often parasites, for example, Giardia intestinalis  Move using multiple flagella © 2014 Pearson Education, Inc.
 Parabasalids  Have reduced mitochondria called hydrogenosomes that generate some energy anaerobically  Include Trichomonas vaginalis, a sexually transmitted parasite © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.10 The parabasalid parasite, Trichomonas vaginalis (colorized SEM) Undulating membrane Flagella 5µm
Euglenozoans  Euglenozoa is a diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and parasites  The main feature distinguishing them as a clade is a spiral or crystalline rod inside their flagella  This clade includes the euglenids and kinetoplastids © 2014 Pearson Education, Inc. Video: Euglena Motion Video: Euglena
© 2014 Pearson Education, Inc. Figure 25.11 Euglenozoan flagellum Ring of microtubules (cross section) Crystalline rod (cross section) 8 µm 0.2 µm Flagella
© 2014 Pearson Education, Inc. Figure 25.11a Ring of microtubules (cross section) Crystalline rod (cross section) 0.2 µm
 Euglenids have one or two flagella that emerge from a pocket at one end of the cell  Some species can be both autotrophic and heterotrophic © 2014 Pearson Education, Inc.
 Kinetoplastids have a single mitochondrion with an organized mass of DNA called a kinetoplast  They include free-living consumers of prokaryotes in aquatic ecosystems and parasites of animals, plants, and other protists  This group includes Trypanosoma, which causes sleeping sickness in humans © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.12 Trypanosoma, the kinetoplastid that causes sleeping sickness 9 µm
The “SAR” Clade  The “SAR” clade is a diverse monophyletic supergroup named for the first letters of its three major clades, stramenopiles, alveolates, and rhizarians © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.UN03 Archaeplastida Unikonta SARclade Rhizarians Alveolates Stramenopiles Excavata Diatoms Brown algae Dinoflagellates Apicomplexans Ciliates Forams Cercozoans
Stramenopiles  The subgroup stramenopiles includes the most important photosynthetic organisms on Earth  Diatoms and brown algae are members of the stramenopiles clade  Diatoms are highly diverse, unicellular algae with a unique two-part, glass-like wall of silicon dioxide © 2014 Pearson Education, Inc. Video: Various Diatoms Video: Diatoms Moving
© 2014 Pearson Education, Inc. Figure 25.13 The diatom Triceratium morlandii (colorized SEM) 40µm
 Brown algae are the largest and most complex algae  All are multicellular, and most are marine  Brown algae include many species commonly called “seaweeds” © 2014 Pearson Education, Inc.
 Brown algal seaweeds have plantlike structures: the rootlike holdfast, which anchors the alga, and a stemlike stipe, which supports the leaflike blades  Similarities between algae and plants are examples of analogous structures © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.14 Blade Stipe Holdfast
Alveolates  The alveolates are a subgroup of the SAR clade that have membrane-bounded sacs (alveoli) just under the plasma membrane  Dinoflagellates and ciliates are members of the alveolata clade © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.15 Flagellum Alveoli Alveolate 0.2µm
© 2014 Pearson Education, Inc. Figure 25.15a Flagellum Alveoli 0.2µm
 Dinoflagellates have two flagella, and each cell is reinforced by cellulose plates  They are abundant components of both marine and freshwater phytoplankton  They are a diverse group of aquatic phototrophs, mixotrophs, and heterotrophs  Toxic “red tides” are caused by dinoflagellate blooms © 2014 Pearson Education, Inc. Video: Dinoflagellate
© 2014 Pearson Education, Inc. Figure 25.16 Flagella Pfiesteria shumwayae, a dinoflagellate 3µm
 Ciliates, a large varied group of protists, are named for their use of cilia to move and feed  Most ciliates are predators of bacteria or small protists © 2014 Pearson Education, Inc. Video: Paramecium Cilia Video: Paramecium Vacuole Video: Vorticella Cilia Video: Vorticella Habitat Video: Vorticella Detail
© 2014 Pearson Education, Inc. Figure 25.17 Contractile vacuole Cilia Oral groove Cell mouth Micronucleus Food vacuolesMacronucleus 50 µm
© 2014 Pearson Education, Inc. Figure 25.17a 50 µm
 Many species of rhizarians are amoebas  Amoebas move and feed by pseudopodia; some but not all belong to the clade Rhizaria  Forams and cercozoans are members of the rhizarian clade Rhizarians © 2014 Pearson Education, Inc.
 Foraminiferans, or forams, are named for porous shells, called tests  Pseudopodia extend through the pores in the test  Many forams have endosymbiotic algae  Forams include both marine and freshwater species © 2014 Pearson Education, Inc.
 Cercozoans include amoeboid and flagellated protists with threadlike pseudopodia  They are common in marine, freshwater, and soil ecosystems  Most are heterotrophs, including parasites and predators © 2014 Pearson Education, Inc.
 Paulinella chromatophora is an autotroph with a unique photosynthetic structure called a chromatophore  This structure evolved from a different cyanobacterium than the plastids of other photosynthetic eukaryotes © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.18 5 µm Chromatophore
Archaeplastids  Plastids arose when a heterotrophic protist acquired a cyanobacterial endosymbiont  The photosynthetic descendants of this ancient protist evolved into red algae and green algae  Land plants are descended from the green algae  Archaeplastida is the supergroup that includes red algae, green algae, and land plants © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.UN04 Archaeplastida Unikonta SAR clade Excavata Chlorophytes Charophytes Red algae Green algae Land plants
Red Algae  Red algae are reddish in color due to an accessory pigment called phycoerythrin, which masks the green of chlorophyll  The color varies from greenish-red in shallow water to dark red or almost black in deep water  Red algae are usually multicellular; the largest are seaweeds  Red algae are the most abundant large algae in coastal waters of the tropics  Red algae reproduce sexually © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.19 Bonnemaisonia hamifera 8 mm Red algae Nori
© 2014 Pearson Education, Inc. Figure 25.19a Bonnemaisonia hamifera 8 mm
© 2014 Pearson Education, Inc. Figure 25.19b Nori
© 2014 Pearson Education, Inc. Figure 25.19c
Green Algae  Green algae are named for their grass-green chloroplasts  Plants are descended from the green algae  Green algae are a paraphyletic group  The two main groups are charophytes and chlorophytes  Charophytes are most closely related to land plants © 2014 Pearson Education, Inc.
 Most chlorophytes live in fresh water, although many are marine and some are terrestrial  Nearly all species of chlorophytes reproduce sexually  Some unicellular chlorophytes are free-living while others live symbiotically within other eukaryotes  Larger size and greater complexity are found in multicellular species including Volvox and Ulva © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.20 (a) Ulva, or sea lettuce (b) Caulerpa, an intertidal chlorophyte Multicellular chlorophytes 2 cm
© 2014 Pearson Education, Inc. Figure 25.20a (a) Ulva, or sea lettuce 2 cm
© 2014 Pearson Education, Inc. Figure 25.20b (b) Caulerpa, an intertidal chlorophyte
Unikonts  The supergroup Unikonta includes animals, fungi, and some protists  This group includes two clades: the amoebozoans and the opisthokonts (animals, fungi, and related protists)  The root of the eukaryotic tree remains controversial  It is unclear whether unikonts separated from other eukaryotes relatively early or late © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.UN05 Unikonta Archaeplastida SAR clade Excavata Gymnamoebas Slime molds Nucleariids Fungi Animals Choanoflagellates
© 2014 Pearson Education, Inc. Figure 25.21 Results Common ancestor of all eukaryotes Choanoflagellates Animals Fungi Amoebozoans Unikonta Excavata Diplomonads SAR clade Euglenozoans Stramenopiles Alveolates Rhizarians Plants Green algae Red algae Archaeplastida DHFR-TS gene fusion
Amoebozoans  Amoebozoans are amoebas that have lobe- or tube-shaped, rather than threadlike, pseudopodia  Most amoebozoans are free-living, but those that belong to the genus Entamoeba are parasites © 2014 Pearson Education, Inc.
 Slime molds are free-living amoebozoans that were once thought to be fungi  DNA sequence analyses indicate that slime molds belong in the clade Amoebozoa © 2014 Pearson Education, Inc.
 Dictyostelium is an example of a cellular slime mold  Cellular slime molds consist of solitary cells that feed individually but can aggregate to form a fruiting body © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.22 Spores (n) Fruiting bodies (n) Emerging amoeba (n) Solitary amoebas (feeding stage) (n) ASEXUAL REPRODUCTION SEXUAL REPRODUCTION MEIOSIS FERTILIZATION Zygote (2n) Amoebas (n) Aggregated amoebas 600 µm Migrating aggregate 200 µm Key Haploid (n) Diploid (2n)
© 2014 Pearson Education, Inc. Figure 25.22a-1 Solitary amoebas (feeding stage) (n) SEXUAL REPRODUCTION FERTILIZATION Zygote (2n) Key Haploid (n) Diploid (2n)
© 2014 Pearson Education, Inc. Figure 25.22a-2 Solitary amoebas (feeding stage) (n) SEXUAL REPRODUCTION MEIOSIS FERTILIZATION Zygote (2n) Amoebas (n) Key Haploid (n) Diploid (2n)
© 2014 Pearson Education, Inc. Figure 25.22a-3 Solitary amoebas (feeding stage) (n) ASEXUAL REPRODUCTION SEXUAL REPRODUCTION MEIOSIS FERTILIZATION Zygote (2n) Amoebas (n) Aggregated amoebas Key Haploid (n) Diploid (2n)
© 2014 Pearson Education, Inc. Figure 25.22a-4 Fruiting bodies (n) Solitary amoebas (feeding stage) (n) ASEXUAL REPRODUCTION SEXUAL REPRODUCTION MEIOSIS FERTILIZATION Zygote (2n) Amoebas (n) Aggregated amoebas Migrating aggregate Key Haploid (n) Diploid (2n)
© 2014 Pearson Education, Inc. Figure 25.22a-5 Spores (n) Fruiting bodies (n) Emerging amoeba (n) Solitary amoebas (feeding stage) (n) ASEXUAL REPRODUCTION SEXUAL REPRODUCTION MEIOSIS FERTILIZATION Zygote (2n) Amoebas (n) Aggregated amoebas Migrating aggregate Key Haploid (n) Diploid (2n)
© 2014 Pearson Education, Inc. Figure 25.22b 200 µm
© 2014 Pearson Education, Inc. Figure 25.22c 600 µm
Opisthokonts  Opisthokonts include animals, fungi, and several groups of protists © 2014 Pearson Education, Inc.
Concept 25.4: Single-celled eukaryotes play key roles in ecological communities and affect human health  The majority of the eukaryotic lineages are composed of protists  Protists exhibit a wide range of structural and functional diversity © 2014 Pearson Education, Inc.
Structural and Functional Diversity in Protists  Single-celled protists can be very complex, as all biological functions are carried out by organelles in each individual cell © 2014 Pearson Education, Inc.
 Protists are found in diverse aquatic environments  Some protists reproduce asexually, while others reproduce sexually, or by the sexual processes of meiosis and fertilization © 2014 Pearson Education, Inc.
 Protists show a wide range of nutritional diversity, including  Photoautotrophs, which contain chloroplasts  Heterotrophs, which absorb organic molecules or ingest larger food particles  Mixotrophs, which combine photosynthesis and heterotrophic nutrition © 2014 Pearson Education, Inc.
Photosynthetic Protists  Many protists are important producers that obtain energy from the sun  In aquatic environments, photosynthetic protists and prokaryotes are the main producers  In aquatic environments, photosynthetic protists are limited by nutrients  These populations can explode when limiting nutrients are added © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.23 Other consumers Herbivorous plankton Carnivorous plankton Protistan producers Prokaryotic producers
 Diatoms are a major component of the phytoplankton  After a diatom population has bloomed, many dead individuals fall to the ocean floor undecomposed  This removes carbon dioxide from the atmosphere and “pumps” it to the ocean floor © 2014 Pearson Education, Inc.
 The biomass and growth of photosynthetic protists and prokaryotes have declined as sea surface temperature has increased  Warmer surface temperatures may prevent nutrient upwelling, a process critical to the growth of marine producers © 2014 Pearson Education, Inc.
 If sea surface temperature continues to warm due to global warming, this could have large effects on  Marine ecosystems  Fishery yields  The global carbon cycle © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.24 NI SI S SP SA EA NA AEPNP Sea-surface temperature (SST) change (°C) −2.50 −1.25 0.00 1.25 2.50 (a) (b) Southern (S) South Pacific (SP) Equatorial Pacific (EP) North Pacific (NP) South Indian (SI) North Indian (NI) South Atlantic (SA) Equatorial Atlantic (EA) North Atlantic (NA) Arctic (A) Chlorophyll change (mg/m2 • yr) −0.02 −0.01 0.00 0.01 0.02
© 2014 Pearson Education, Inc. Figure 25.24a Sea-surface temperature (SST) change (°C) −2.50 −1.25 0.00 1.25 2.50 SA SP EA NA AEPNP NI SI S (a)
© 2014 Pearson Education, Inc. Figure 25.24b −0.02 −0.01 0.00 0.01 0.02 Southern (S) South Pacific (SP) Equatorial Pacific (EP) North Pacific (NP) South Indian (SI) North Indian (NI) South Atlantic (SA) Equatorial Atlantic (EA) North Atlantic (NA) Arctic (A) Chlorophyll change (mg/m2 • yr) (b)
Symbiotic Protists  Some protist symbionts benefit their hosts  Dinoflagellates nourish coral polyps that build reefs  Wood-digesting protists digest cellulose in the gut of termites © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. 10µm Figure 25.25
 Some protists are parasitic  Plasmodium causes malaria  Pfiesteria shumwayae is a dinoflagellate that causes fish kills  Phytophthora ramorum causes sudden oak death  Phytophthora infestans causes potato late blight © 2014 Pearson Education, Inc.
Effects on Human Health  Protists that cause infectious disease can pose major challenges to human immune systems and public health  Trypanosoma is an excavate that causes sleeping sickness in humans © 2014 Pearson Education, Inc.
 Trypanosomes evade immune responses by switching surface proteins  A cell produces millions of copies of a single protein  The new generation produces millions of copies of a different protein  These frequent changes prevent the host from developing immunity © 2014 Pearson Education, Inc.
 Entamoebas are amoebozoan parasites of vertebrates and some invertebrates  Entamoeba histolytica causes amebic dysentery, the third-leading cause of human death due to eukaryotic parasites © 2014 Pearson Education, Inc.
 Apicomplexans are alveolate parasites of animals, and some cause serious human diseases  Most have sexual and asexual stages that require two or more different host species for completion © 2014 Pearson Education, Inc.
 The apicomplexan Plasmodium is the parasite that causes malaria  Plasmodium requires both mosquitoes and humans to complete its life cycle  Approximately 900,000 people die each year from malaria  Efforts are ongoing to develop vaccines that target this pathogen © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc. Figure 25.26 0.5 µm Apex Red blood cell Merozoite Liver Liver cell Red blood cells Merozoite (n) Zygote (2n) Oocyst MEIOSIS Sporozoites (n) Inside mosquito Inside human FERTILIZATION Gametes Gametocytes (n) Key Haploid (n) Diploid (2n)
© 2014 Pearson Education, Inc. Figure 25.26a 0.5 µm Apex Red blood cell Merozoite
© 2014 Pearson Education, Inc. Figure 25.UN01
© 2014 Pearson Education, Inc. Figure 25.UN06

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Biology in Focus - Chapter 25

  • 1.
    CAMPBELL BIOLOGY INFOCUS © 2014 Pearson Education, Inc. Urry • Cain • Wasserman • Minorsky • Jackson • Reece Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge 25 The Origin and Diversification of Eukaryotes
  • 2.
    Overview: Shape Changers Protist is the informal name of the diverse group of mostly unicellular eukaryotes  Some protists, like the ciliate Didinium, are able to perform dramatic shape changes due to the structural complexity of their cells © 2014 Pearson Education, Inc.
  • 3.
    © 2014 PearsonEducation, Inc. Figure 25.1
  • 4.
    Concept 25.1: Eukaryotesarose by endosymbiosis more than 1.8 billion years ago  Early eukaryotes were unicellular  Eukaryotic cells have organelles and are structurally more complex than prokaryotic cells  A well-developed cytoskeleton enables eukaryotic cells to have asymmetrical forms and to change shape © 2014 Pearson Education, Inc.
  • 5.
    The Fossil Recordof Early Eukaryotes  Chemical evidence for the presence of eukaryotes dates back to 2.7 billion years ago  The earliest fossils of eukaryotic cells are 1.8 billion years old © 2014 Pearson Education, Inc.
  • 6.
     Initial diversificationof eukaryotes occurred 1.8 to 1.3 billion years ago  Novel features of eukaryotes, including complex multicellularity, sexual life cycles, and photosynthesis, arose 1.3 billion to 635 million years ago  The first large, multicellular eukaryotes represented by the Ediacaran biota evolved 635 to 535 million years ago © 2014 Pearson Education, Inc.
  • 7.
    © 2014 PearsonEducation, Inc. Figure 25.2 4.5 bya 3.5 1.52.5 500 mya 1.8 bya 1.5 bya 1.3 bya 1.2 bya 20 µm 20µm 25 µm 25 µm (a) A 1.8-billion- year-old fossil eukaryote (b) Tappania, a 1.5-billion-year-old fossil that may represent an early alga or fungus (c) Bangiomorpha, an ancient red alga 20µm (d) Proterocladus, classified as a green alga (e) Bonneia, a vase-shaped eukaryote (f) An early member of the Ediacaran biota (g) Spriggina floundersi, an early animal with many body segments 750 mya 635 mya 600 mya 550 mya 535 mya 1 cm 0.5 cm
  • 8.
    © 2014 PearsonEducation, Inc. Figure 25.2a 4.5 bya 3.5 1.52.5 500 mya 1.8 bya 1.5 bya 20 µm 20µm (a) A 1.8-billion- year-old fossil eukaryote (b) Tappania, a 1.5-billion-year-old fossil that may represent an early alga or fungus Initial diversification
  • 9.
    © 2014 PearsonEducation, Inc. Figure 25.2aa 20 µm (a) A 1.8-billion-year-old fossil eukaryote
  • 10.
    © 2014 PearsonEducation, Inc. Figure 25.2ab (b) Tappania, a 1.5-billion-year-old fossil that may represent an early alga or fungus 20µm
  • 11.
    © 2014 PearsonEducation, Inc. Figure 25.2b 4.5 bya 3.5 1.52.5 500 mya Appearance of novel features 1.3 bya 1.2 bya 750 mya 20µm 25 µm 25 µm (c) Bangiomorpha, an ancient red alga (d) Proterocladus, classified as a green alga (e) Bonneia, a vase-shaped eukaryote
  • 12.
    © 2014 PearsonEducation, Inc. Figure 25.2ba 25 µm (c) Bangiomorpha, an ancient red alga
  • 13.
    © 2014 PearsonEducation, Inc. Figure 25.2bb 25 µm (d) Proterocladus, classified as a green alga
  • 14.
    © 2014 PearsonEducation, Inc. Figure 25.2bc 20µm (e) Bonneia, a vase-shaped eukaryote
  • 15.
    © 2014 PearsonEducation, Inc. Figure 25.2c 4.5 bya 3.5 1.52.5 500 mya Rise of large eukaryotes 635 mya 600 mya 550 mya 535 mya 1 cm 0.5 cm (f) An early member of the Ediacaran biota (g) Spriggina floundersi, an early animal with many body segments
  • 16.
    © 2014 PearsonEducation, Inc. Figure 25.2ca 1 cm (f) An early member of the Ediacaran biota
  • 17.
    © 2014 PearsonEducation, Inc. Figure 25.2cb 0.5 cm (g) Spriggina floundersi, an early animal with many body segments
  • 18.
     Eukaryotic cellsexhibited greater structural complexity than prokaryotic cells as early as 1.5 billion years ago  The earliest multicellular eukaryotic fossils are of red algae, which date back to 1.2 billion years ago, but large, multicellular eukaryotes did not arise until 635 million years ago  Severe ice ages from 750 to 580 million years ago may have hindered the rise of large eukaryotes © 2014 Pearson Education, Inc.
  • 19.
    Endosymbiosis in EukaryoticEvolution  DNA sequence data indicate that eukaryotes are “combination” organisms  Eukaryotic genes and characteristics show evidence of both archaeal and bacterial origins  Evidence of mixed origins may be a consequence of endosymbiosis, a symbiotic relationship in which one organism lives inside the body or cell of another organism © 2014 Pearson Education, Inc.
  • 20.
    © 2014 PearsonEducation, Inc. Table 25.1
  • 21.
    Origin of Mitochondriaand Plastids  Endosymbiont theory proposes that mitochondria and plastids were formerly small prokaryotes that began living within larger cells  An endosymbiont is a cell that lives within a host cell  Prokaryote ancestors to mitochondria and plastids probably entered the host cell as undigested prey or internal parasites © 2014 Pearson Education, Inc.
  • 22.
     The relationshipbetween endosymbiont and host cells was mutually beneficial  Anaerobic host cells benefited from endosymbionts’ ability to take advantage of an increasingly aerobic world  Heterotrophic host cells benefited from the nutrients produced by photosynthetic endosymbionts  In the process of becoming more interdependent, the host and endosymbionts would have become a single organism © 2014 Pearson Education, Inc.
  • 23.
     Serial endosymbiosissupposes that mitochondria evolved before plastids through a sequence of endosymbiotic events © 2014 Pearson Education, Inc.
  • 24.
    © 2014 PearsonEducation, Inc. Figure 25.3 Cytoplasm DNA Nucleus Engulfing of aerobic bacterium Engulfing of photo- synthetic bacterium Mitochondrion Mito- chondrion Plastid Plasma membrane Endoplasmic reticulum Nuclear envelope Ancestral prokaryote Ancestral heterotrophic eukaryote Ancestral photosynthetic eukaryote
  • 25.
     Key evidencesupporting an endosymbiotic origin of mitochondria and plastids:  Inner membranes are similar to plasma membranes of prokaryotes  Division is similar in these organelles and some prokaryotes  DNA structure is similar to that of prokaryotes  These organelles transcribe and translate their own DNA  Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes © 2014 Pearson Education, Inc.
  • 26.
     DNA sequenceanalysis indicates that mitochondria arose from an alpha proteobacterium  Eukaryotic mitochondria descended from a single common ancestor  Plastids arose from an engulfed cyanobacterium  Some photosynthetic protists may have been engulfed to become endosymbionts themselves © 2014 Pearson Education, Inc.
  • 27.
     The ancestralhost cell may have been an archaean or a “protoeukaryote,” from a lineage related to, but diverged from, archaeal ancestors © 2014 Pearson Education, Inc.
  • 28.
    Plastid Evolution: ACloser Look  There is now considerable evidence that much protist diversity has its origins in endosymbiosis  Mitochondria arose first through descent from a bacterium that was engulfed by a cell from an archaeal lineage  The plastid lineage evolved later from a photosynthetic cyanobacterium that was engulfed by a heterotrophic eukaryote © 2014 Pearson Education, Inc.
  • 29.
    © 2014 PearsonEducation, Inc. Figure 25.4 Cyano- bacterium Membranes are represented as dark lines in the cell. Red alga Primary endo- symbiosis 1 2 3 Nucleus Heterotrophic eukaryote One of these membranes was lost in red and green algal descendants. Green alga Secondary endo- symbiosis Secondary endo- symbiosis Plastid Euglenids Chlorarachniophytes Stramenopiles Plastid Secondary endo- symbiosis Dinoflagellates
  • 30.
    © 2014 PearsonEducation, Inc. Figure 25.4a Cyano- bacterium Membranes are represented as dark lines in the cell. Red alga Primary endosymbiosis 1 2 3 Nucleus Heterotrophic eukaryote One of these membranes was lost in red and green algal descendants. Green alga
  • 31.
    © 2014 PearsonEducation, Inc. Figure 25.4b Secondary endosymbiosis Red alga Plastid Dinoflagellates Stramenopiles
  • 32.
    © 2014 PearsonEducation, Inc. Figure 25.4c Secondary endosymbiosis Plastid Euglenids Green alga Chlorarachniophytes
  • 33.
     The plastid-bearinglineage of protists evolved into red and green algae  Like cyanobacteria, plastids of red algae and green algae have two membranes  Transport proteins in the membranes of red and green algae are homologous to those found in cyanobacteria  On several occasions during eukaryotic evolution, red and green algae underwent secondary endosymbiosis, in which they were ingested by a heterotrophic eukaryote © 2014 Pearson Education, Inc.
  • 34.
    Concept 25.2: Multicellularityhas originated several times in eukaryotes  The evolution of eukaryotic cells allowed for a greater range of unicellular forms  A second wave of diversification occurred when multicellularity evolved and gave rise to algae, plants, fungi, and animals © 2014 Pearson Education, Inc.
  • 35.
    Multicellular Colonies  Thefirst multicellular forms were colonies, collections of cells that are connected to one another but show little or no cellular differentiation  Multicellular colonies consist of simple filaments, balls, or cell sheets  Colonial cells may be attached by shared cell walls or, in cells that lack rigid walls, held together by proteins that physically connect adjacent cells © 2014 Pearson Education, Inc.
  • 36.
    © 2014 PearsonEducation, Inc. Figure 25.5 Pediastrum
  • 37.
    Independent Origins ofComplex Multicellularity  Multicellular organisms with differentiated cells originated multiple times over the course of eukaryotic evolution  Genetic and morphological evidence indicates that lineages of red, green, and brown algae, plants, fungi, and animals arose independently from different single-celled ancestors © 2014 Pearson Education, Inc.
  • 38.
     Volvox isa multicellular green algae that forms a monophyletic group with a single-celled alga (Chlamydomonas) and several colonial species  Volvox and all colonial members of this group have proteins homologous to those found in the cell wall of Chlamydomonas  Multicellularity in Volvox may have originated through evolution of increasingly complex colonial forms descended from a single-celled common ancestor © 2014 Pearson Education, Inc. Video: Chlamydomonas
  • 39.
    © 2014 PearsonEducation, Inc. Figure 25.6 Flagellum Cytoplasm Outer cell wall Inner cell wall Outer cell wall Cytoplasm Extracellular matrix (ECM) Chlamydomonas Gonium Pandorina Volvox
  • 40.
     Only afew novel genes account for morphological differences between Volvox and Chlamydomonas  The transition to multicellularity may result from changes in how existing genes are used rather than the origin of large numbers of novel genes © 2014 Pearson Education, Inc.
  • 41.
    Steps in theOrigin of Multicellular Animals  Choanoflagellates are the closest living relatives of animals  The common ancestor of choanoflagellates and living animals may have resembled present-day choanoflagellates © 2014 Pearson Education, Inc.
  • 42.
    © 2014 PearsonEducation, Inc. Figure 25.7 Individual choanoflagellate Choano- flagellates Other animals Collar cell (choanocyte) Sponges Animals OTHER EUKARY- OTES
  • 43.
     The originof multicellularity in animals required mechanisms for cells to adhere to each other and to communicate with each other (cell signaling)  Molecular similarities in domains of proteins functioning in cell adherence (cadherins) and cell signaling have been found between modern choanoflagellates and representative animals © 2014 Pearson Education, Inc.
  • 44.
    © 2014 PearsonEducation, Inc. Figure 25.8 Hydra Mouse “CCD” domain Choano- flagellate Fruit fly
  • 45.
     The transitionto multicellularity in animals involved new ways of using proteins encoded by genes found in choanoflagellates rather than the evolution of many novel genes © 2014 Pearson Education, Inc.
  • 46.
    Concept 25.3: Four“supergroups” of eukaryotes have been proposed based on morphological and molecular data  Eukaryote diversity is influenced by their hybrid origins and the independent origins of complex multicellularity  One hypothesis divides all eukaryotes into four supergroups © 2014 Pearson Education, Inc.
  • 47.
    Four Supergroups ofEukaryotes  It is no longer thought that amitochondriates (lacking mitochondria) are the oldest lineage of eukaryotes  Many have been shown to have mitochondria and have been reclassified  Our understanding of the relationships among protist groups continues to change rapidly  One hypothesis divides all eukaryotes (including protists) into four supergroups © 2014 Pearson Education, Inc.
  • 48.
    © 2014 PearsonEducation, Inc. Video: Amoeba Pseudopodia Video: Volvox Colony Video: Amoeba Video: Volvox Female Spheroid Video: Volvox Flagella Video: Volvox Daughter Video: Volvox Inversion 1 Video: Volvox Sperm Video: Volvox Inversion 2
  • 49.
    © 2014 PearsonEducation, Inc. Figure 25.9 Stramen- opiles Diplomonads Parabasalids Euglenozoans Excavata Alveo- lates Rhiza- rians Diatoms Brown algae Dinoflagellates Apicomplexans Ciliates Forams Cercozoans “SAR”clade Green algae Amoebo- zoans Red algae Chlorophytes Charophytes Land plants Archaeplastida Opisthokonts Unikonta Gymnamoebas Slime molds Nucleariids Fungi Choanoflagellates Animals 100 µm 50 µm “SAR” Clade Excavata 5 µm Archaeplastida 20 µm 50 µm Unikonta 100 µm
  • 50.
    © 2014 PearsonEducation, Inc. Figure 25.9a Stramen- opiles Diplomonads Parabasalids Euglenozoans Excavata Alveo- lates Rhiza- rians Diatoms Brown algae Dinoflagellates Apicomplexans Ciliates Forams Cercozoans “SAR”clade Green algae Amoebo- zoans Red algae Chlorophytes Charophytes Land plants Archaeplastida Opisthokonts Unikonta Gymnamoebas Slime molds Nucleariids Fungi Choanoflagellates Animals
  • 51.
    © 2014 PearsonEducation, Inc. Figure 25.9aa Stramen- opiles Diplomonads Parabasalids Euglenozoans Excavata Alveo- lates Rhiza- rians Diatoms Brown algae Dinoflagellates Apicomplexans Ciliates Forams Cercozoans “SAR”clade
  • 52.
    © 2014 PearsonEducation, Inc. Figure 25.9ab Green algae Amoebo- zoans Red algae Chlorophytes Charophytes Land plants Archaeplastida Opisthokonts Unikonta Gymnamoebas Slime molds Nucleariids Fungi Choanoflagellates Animals
  • 53.
    © 2014 PearsonEducation, Inc. Figure 25.9b Excavata “SAR” Clade Archaeplastida 50 µm 50 µm 20 µm 5 µm Unikonta 100 µm 100 µm
  • 54.
    © 2014 PearsonEducation, Inc. Figure 25.9ba Giardia intestinalis, a diplomonad parasite 5 µm
  • 55.
    © 2014 PearsonEducation, Inc. Figure 25.9bb Diatom diversity 50 µm
  • 56.
    © 2014 PearsonEducation, Inc. Figure 25.9bc Globigerina, a rhizarian in the SAR supergroup 100 µm
  • 57.
    © 2014 PearsonEducation, Inc. Figure 25.9bca Globigerina, a rhizarian in the SAR supergroup 100 µm
  • 58.
    © 2014 PearsonEducation, Inc. Figure 25.9bcb
  • 59.
    © 2014 PearsonEducation, Inc. Figure 25.9bd Volvox, a multicellular freshwater green alga 20 µm 50 µm
  • 60.
    © 2014 PearsonEducation, Inc. Figure 25.9bda Volvox, a multicellular freshwater green alga 50 µm
  • 61.
    © 2014 PearsonEducation, Inc. Figure 25.9bdb 20 µm
  • 62.
    © 2014 PearsonEducation, Inc. Figure 25.9be 100 µm A unikont amoeba
  • 63.
    Excavates  The supergroupExcavata is characterized by its cytoskeleton  Some members have a feeding groove  This monophyletic group includes the diplomonads, parabasalids, and euglenozoans © 2014 Pearson Education, Inc.
  • 64.
    © 2014 PearsonEducation, Inc. Figure 25.UN02 Diplomonads Parabasalids Euglenozoans Excavata SAR clade Archaeplastida Unikonta
  • 65.
    Diplomonads and Parabasalids These two groups lack plastids and have modified mitochondria, and most live in anaerobic environments  Diplomonads  Have reduced mitochondria called mitosomes  Derive energy from anaerobic biochemical pathways  Are often parasites, for example, Giardia intestinalis  Move using multiple flagella © 2014 Pearson Education, Inc.
  • 66.
     Parabasalids  Havereduced mitochondria called hydrogenosomes that generate some energy anaerobically  Include Trichomonas vaginalis, a sexually transmitted parasite © 2014 Pearson Education, Inc.
  • 67.
    © 2014 PearsonEducation, Inc. Figure 25.10 The parabasalid parasite, Trichomonas vaginalis (colorized SEM) Undulating membrane Flagella 5µm
  • 68.
    Euglenozoans  Euglenozoa isa diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and parasites  The main feature distinguishing them as a clade is a spiral or crystalline rod inside their flagella  This clade includes the euglenids and kinetoplastids © 2014 Pearson Education, Inc. Video: Euglena Motion Video: Euglena
  • 69.
    © 2014 PearsonEducation, Inc. Figure 25.11 Euglenozoan flagellum Ring of microtubules (cross section) Crystalline rod (cross section) 8 µm 0.2 µm Flagella
  • 70.
    © 2014 PearsonEducation, Inc. Figure 25.11a Ring of microtubules (cross section) Crystalline rod (cross section) 0.2 µm
  • 71.
     Euglenids haveone or two flagella that emerge from a pocket at one end of the cell  Some species can be both autotrophic and heterotrophic © 2014 Pearson Education, Inc.
  • 72.
     Kinetoplastids havea single mitochondrion with an organized mass of DNA called a kinetoplast  They include free-living consumers of prokaryotes in aquatic ecosystems and parasites of animals, plants, and other protists  This group includes Trypanosoma, which causes sleeping sickness in humans © 2014 Pearson Education, Inc.
  • 73.
    © 2014 PearsonEducation, Inc. Figure 25.12 Trypanosoma, the kinetoplastid that causes sleeping sickness 9 µm
  • 74.
    The “SAR” Clade The “SAR” clade is a diverse monophyletic supergroup named for the first letters of its three major clades, stramenopiles, alveolates, and rhizarians © 2014 Pearson Education, Inc.
  • 75.
    © 2014 PearsonEducation, Inc. Figure 25.UN03 Archaeplastida Unikonta SARclade Rhizarians Alveolates Stramenopiles Excavata Diatoms Brown algae Dinoflagellates Apicomplexans Ciliates Forams Cercozoans
  • 76.
    Stramenopiles  The subgroupstramenopiles includes the most important photosynthetic organisms on Earth  Diatoms and brown algae are members of the stramenopiles clade  Diatoms are highly diverse, unicellular algae with a unique two-part, glass-like wall of silicon dioxide © 2014 Pearson Education, Inc. Video: Various Diatoms Video: Diatoms Moving
  • 77.
    © 2014 PearsonEducation, Inc. Figure 25.13 The diatom Triceratium morlandii (colorized SEM) 40µm
  • 78.
     Brown algaeare the largest and most complex algae  All are multicellular, and most are marine  Brown algae include many species commonly called “seaweeds” © 2014 Pearson Education, Inc.
  • 79.
     Brown algalseaweeds have plantlike structures: the rootlike holdfast, which anchors the alga, and a stemlike stipe, which supports the leaflike blades  Similarities between algae and plants are examples of analogous structures © 2014 Pearson Education, Inc.
  • 80.
    © 2014 PearsonEducation, Inc. Figure 25.14 Blade Stipe Holdfast
  • 81.
    Alveolates  The alveolatesare a subgroup of the SAR clade that have membrane-bounded sacs (alveoli) just under the plasma membrane  Dinoflagellates and ciliates are members of the alveolata clade © 2014 Pearson Education, Inc.
  • 82.
    © 2014 PearsonEducation, Inc. Figure 25.15 Flagellum Alveoli Alveolate 0.2µm
  • 83.
    © 2014 PearsonEducation, Inc. Figure 25.15a Flagellum Alveoli 0.2µm
  • 84.
     Dinoflagellates havetwo flagella, and each cell is reinforced by cellulose plates  They are abundant components of both marine and freshwater phytoplankton  They are a diverse group of aquatic phototrophs, mixotrophs, and heterotrophs  Toxic “red tides” are caused by dinoflagellate blooms © 2014 Pearson Education, Inc. Video: Dinoflagellate
  • 85.
    © 2014 PearsonEducation, Inc. Figure 25.16 Flagella Pfiesteria shumwayae, a dinoflagellate 3µm
  • 86.
     Ciliates, alarge varied group of protists, are named for their use of cilia to move and feed  Most ciliates are predators of bacteria or small protists © 2014 Pearson Education, Inc. Video: Paramecium Cilia Video: Paramecium Vacuole Video: Vorticella Cilia Video: Vorticella Habitat Video: Vorticella Detail
  • 87.
    © 2014 PearsonEducation, Inc. Figure 25.17 Contractile vacuole Cilia Oral groove Cell mouth Micronucleus Food vacuolesMacronucleus 50 µm
  • 88.
    © 2014 PearsonEducation, Inc. Figure 25.17a 50 µm
  • 89.
     Many speciesof rhizarians are amoebas  Amoebas move and feed by pseudopodia; some but not all belong to the clade Rhizaria  Forams and cercozoans are members of the rhizarian clade Rhizarians © 2014 Pearson Education, Inc.
  • 90.
     Foraminiferans, orforams, are named for porous shells, called tests  Pseudopodia extend through the pores in the test  Many forams have endosymbiotic algae  Forams include both marine and freshwater species © 2014 Pearson Education, Inc.
  • 91.
     Cercozoans includeamoeboid and flagellated protists with threadlike pseudopodia  They are common in marine, freshwater, and soil ecosystems  Most are heterotrophs, including parasites and predators © 2014 Pearson Education, Inc.
  • 92.
     Paulinella chromatophorais an autotroph with a unique photosynthetic structure called a chromatophore  This structure evolved from a different cyanobacterium than the plastids of other photosynthetic eukaryotes © 2014 Pearson Education, Inc.
  • 93.
    © 2014 PearsonEducation, Inc. Figure 25.18 5 µm Chromatophore
  • 94.
    Archaeplastids  Plastids arosewhen a heterotrophic protist acquired a cyanobacterial endosymbiont  The photosynthetic descendants of this ancient protist evolved into red algae and green algae  Land plants are descended from the green algae  Archaeplastida is the supergroup that includes red algae, green algae, and land plants © 2014 Pearson Education, Inc.
  • 95.
    © 2014 PearsonEducation, Inc. Figure 25.UN04 Archaeplastida Unikonta SAR clade Excavata Chlorophytes Charophytes Red algae Green algae Land plants
  • 96.
    Red Algae  Redalgae are reddish in color due to an accessory pigment called phycoerythrin, which masks the green of chlorophyll  The color varies from greenish-red in shallow water to dark red or almost black in deep water  Red algae are usually multicellular; the largest are seaweeds  Red algae are the most abundant large algae in coastal waters of the tropics  Red algae reproduce sexually © 2014 Pearson Education, Inc.
  • 97.
    © 2014 PearsonEducation, Inc. Figure 25.19 Bonnemaisonia hamifera 8 mm Red algae Nori
  • 98.
    © 2014 PearsonEducation, Inc. Figure 25.19a Bonnemaisonia hamifera 8 mm
  • 99.
    © 2014 PearsonEducation, Inc. Figure 25.19b Nori
  • 100.
    © 2014 PearsonEducation, Inc. Figure 25.19c
  • 101.
    Green Algae  Greenalgae are named for their grass-green chloroplasts  Plants are descended from the green algae  Green algae are a paraphyletic group  The two main groups are charophytes and chlorophytes  Charophytes are most closely related to land plants © 2014 Pearson Education, Inc.
  • 102.
     Most chlorophyteslive in fresh water, although many are marine and some are terrestrial  Nearly all species of chlorophytes reproduce sexually  Some unicellular chlorophytes are free-living while others live symbiotically within other eukaryotes  Larger size and greater complexity are found in multicellular species including Volvox and Ulva © 2014 Pearson Education, Inc.
  • 103.
    © 2014 PearsonEducation, Inc. Figure 25.20 (a) Ulva, or sea lettuce (b) Caulerpa, an intertidal chlorophyte Multicellular chlorophytes 2 cm
  • 104.
    © 2014 PearsonEducation, Inc. Figure 25.20a (a) Ulva, or sea lettuce 2 cm
  • 105.
    © 2014 PearsonEducation, Inc. Figure 25.20b (b) Caulerpa, an intertidal chlorophyte
  • 106.
    Unikonts  The supergroupUnikonta includes animals, fungi, and some protists  This group includes two clades: the amoebozoans and the opisthokonts (animals, fungi, and related protists)  The root of the eukaryotic tree remains controversial  It is unclear whether unikonts separated from other eukaryotes relatively early or late © 2014 Pearson Education, Inc.
  • 107.
    © 2014 PearsonEducation, Inc. Figure 25.UN05 Unikonta Archaeplastida SAR clade Excavata Gymnamoebas Slime molds Nucleariids Fungi Animals Choanoflagellates
  • 108.
    © 2014 PearsonEducation, Inc. Figure 25.21 Results Common ancestor of all eukaryotes Choanoflagellates Animals Fungi Amoebozoans Unikonta Excavata Diplomonads SAR clade Euglenozoans Stramenopiles Alveolates Rhizarians Plants Green algae Red algae Archaeplastida DHFR-TS gene fusion
  • 109.
    Amoebozoans  Amoebozoans areamoebas that have lobe- or tube-shaped, rather than threadlike, pseudopodia  Most amoebozoans are free-living, but those that belong to the genus Entamoeba are parasites © 2014 Pearson Education, Inc.
  • 110.
     Slime moldsare free-living amoebozoans that were once thought to be fungi  DNA sequence analyses indicate that slime molds belong in the clade Amoebozoa © 2014 Pearson Education, Inc.
  • 111.
     Dictyostelium isan example of a cellular slime mold  Cellular slime molds consist of solitary cells that feed individually but can aggregate to form a fruiting body © 2014 Pearson Education, Inc.
  • 112.
    © 2014 PearsonEducation, Inc. Figure 25.22 Spores (n) Fruiting bodies (n) Emerging amoeba (n) Solitary amoebas (feeding stage) (n) ASEXUAL REPRODUCTION SEXUAL REPRODUCTION MEIOSIS FERTILIZATION Zygote (2n) Amoebas (n) Aggregated amoebas 600 µm Migrating aggregate 200 µm Key Haploid (n) Diploid (2n)
  • 113.
    © 2014 PearsonEducation, Inc. Figure 25.22a-1 Solitary amoebas (feeding stage) (n) SEXUAL REPRODUCTION FERTILIZATION Zygote (2n) Key Haploid (n) Diploid (2n)
  • 114.
    © 2014 PearsonEducation, Inc. Figure 25.22a-2 Solitary amoebas (feeding stage) (n) SEXUAL REPRODUCTION MEIOSIS FERTILIZATION Zygote (2n) Amoebas (n) Key Haploid (n) Diploid (2n)
  • 115.
    © 2014 PearsonEducation, Inc. Figure 25.22a-3 Solitary amoebas (feeding stage) (n) ASEXUAL REPRODUCTION SEXUAL REPRODUCTION MEIOSIS FERTILIZATION Zygote (2n) Amoebas (n) Aggregated amoebas Key Haploid (n) Diploid (2n)
  • 116.
    © 2014 PearsonEducation, Inc. Figure 25.22a-4 Fruiting bodies (n) Solitary amoebas (feeding stage) (n) ASEXUAL REPRODUCTION SEXUAL REPRODUCTION MEIOSIS FERTILIZATION Zygote (2n) Amoebas (n) Aggregated amoebas Migrating aggregate Key Haploid (n) Diploid (2n)
  • 117.
    © 2014 PearsonEducation, Inc. Figure 25.22a-5 Spores (n) Fruiting bodies (n) Emerging amoeba (n) Solitary amoebas (feeding stage) (n) ASEXUAL REPRODUCTION SEXUAL REPRODUCTION MEIOSIS FERTILIZATION Zygote (2n) Amoebas (n) Aggregated amoebas Migrating aggregate Key Haploid (n) Diploid (2n)
  • 118.
    © 2014 PearsonEducation, Inc. Figure 25.22b 200 µm
  • 119.
    © 2014 PearsonEducation, Inc. Figure 25.22c 600 µm
  • 120.
    Opisthokonts  Opisthokonts includeanimals, fungi, and several groups of protists © 2014 Pearson Education, Inc.
  • 121.
    Concept 25.4: Single-celledeukaryotes play key roles in ecological communities and affect human health  The majority of the eukaryotic lineages are composed of protists  Protists exhibit a wide range of structural and functional diversity © 2014 Pearson Education, Inc.
  • 122.
    Structural and FunctionalDiversity in Protists  Single-celled protists can be very complex, as all biological functions are carried out by organelles in each individual cell © 2014 Pearson Education, Inc.
  • 123.
     Protists arefound in diverse aquatic environments  Some protists reproduce asexually, while others reproduce sexually, or by the sexual processes of meiosis and fertilization © 2014 Pearson Education, Inc.
  • 124.
     Protists showa wide range of nutritional diversity, including  Photoautotrophs, which contain chloroplasts  Heterotrophs, which absorb organic molecules or ingest larger food particles  Mixotrophs, which combine photosynthesis and heterotrophic nutrition © 2014 Pearson Education, Inc.
  • 125.
    Photosynthetic Protists  Manyprotists are important producers that obtain energy from the sun  In aquatic environments, photosynthetic protists and prokaryotes are the main producers  In aquatic environments, photosynthetic protists are limited by nutrients  These populations can explode when limiting nutrients are added © 2014 Pearson Education, Inc.
  • 126.
    © 2014 PearsonEducation, Inc. Figure 25.23 Other consumers Herbivorous plankton Carnivorous plankton Protistan producers Prokaryotic producers
  • 127.
     Diatoms area major component of the phytoplankton  After a diatom population has bloomed, many dead individuals fall to the ocean floor undecomposed  This removes carbon dioxide from the atmosphere and “pumps” it to the ocean floor © 2014 Pearson Education, Inc.
  • 128.
     The biomassand growth of photosynthetic protists and prokaryotes have declined as sea surface temperature has increased  Warmer surface temperatures may prevent nutrient upwelling, a process critical to the growth of marine producers © 2014 Pearson Education, Inc.
  • 129.
     If seasurface temperature continues to warm due to global warming, this could have large effects on  Marine ecosystems  Fishery yields  The global carbon cycle © 2014 Pearson Education, Inc.
  • 130.
    © 2014 PearsonEducation, Inc. Figure 25.24 NI SI S SP SA EA NA AEPNP Sea-surface temperature (SST) change (°C) −2.50 −1.25 0.00 1.25 2.50 (a) (b) Southern (S) South Pacific (SP) Equatorial Pacific (EP) North Pacific (NP) South Indian (SI) North Indian (NI) South Atlantic (SA) Equatorial Atlantic (EA) North Atlantic (NA) Arctic (A) Chlorophyll change (mg/m2 • yr) −0.02 −0.01 0.00 0.01 0.02
  • 131.
    © 2014 PearsonEducation, Inc. Figure 25.24a Sea-surface temperature (SST) change (°C) −2.50 −1.25 0.00 1.25 2.50 SA SP EA NA AEPNP NI SI S (a)
  • 132.
    © 2014 PearsonEducation, Inc. Figure 25.24b −0.02 −0.01 0.00 0.01 0.02 Southern (S) South Pacific (SP) Equatorial Pacific (EP) North Pacific (NP) South Indian (SI) North Indian (NI) South Atlantic (SA) Equatorial Atlantic (EA) North Atlantic (NA) Arctic (A) Chlorophyll change (mg/m2 • yr) (b)
  • 133.
    Symbiotic Protists  Someprotist symbionts benefit their hosts  Dinoflagellates nourish coral polyps that build reefs  Wood-digesting protists digest cellulose in the gut of termites © 2014 Pearson Education, Inc.
  • 134.
    © 2014 PearsonEducation, Inc. 10µm Figure 25.25
  • 135.
     Some protistsare parasitic  Plasmodium causes malaria  Pfiesteria shumwayae is a dinoflagellate that causes fish kills  Phytophthora ramorum causes sudden oak death  Phytophthora infestans causes potato late blight © 2014 Pearson Education, Inc.
  • 136.
    Effects on HumanHealth  Protists that cause infectious disease can pose major challenges to human immune systems and public health  Trypanosoma is an excavate that causes sleeping sickness in humans © 2014 Pearson Education, Inc.
  • 137.
     Trypanosomes evadeimmune responses by switching surface proteins  A cell produces millions of copies of a single protein  The new generation produces millions of copies of a different protein  These frequent changes prevent the host from developing immunity © 2014 Pearson Education, Inc.
  • 138.
     Entamoebas areamoebozoan parasites of vertebrates and some invertebrates  Entamoeba histolytica causes amebic dysentery, the third-leading cause of human death due to eukaryotic parasites © 2014 Pearson Education, Inc.
  • 139.
     Apicomplexans arealveolate parasites of animals, and some cause serious human diseases  Most have sexual and asexual stages that require two or more different host species for completion © 2014 Pearson Education, Inc.
  • 140.
     The apicomplexanPlasmodium is the parasite that causes malaria  Plasmodium requires both mosquitoes and humans to complete its life cycle  Approximately 900,000 people die each year from malaria  Efforts are ongoing to develop vaccines that target this pathogen © 2014 Pearson Education, Inc.
  • 141.
    © 2014 PearsonEducation, Inc. Figure 25.26 0.5 µm Apex Red blood cell Merozoite Liver Liver cell Red blood cells Merozoite (n) Zygote (2n) Oocyst MEIOSIS Sporozoites (n) Inside mosquito Inside human FERTILIZATION Gametes Gametocytes (n) Key Haploid (n) Diploid (2n)
  • 142.
    © 2014 PearsonEducation, Inc. Figure 25.26a 0.5 µm Apex Red blood cell Merozoite
  • 143.
    © 2014 PearsonEducation, Inc. Figure 25.UN01
  • 144.
    © 2014 PearsonEducation, Inc. Figure 25.UN06

Editor's Notes

  • #4 Figure 25.1 What enables the cell on the left to engulf its prey?
  • #8 Figure 25.2 Exploring the early evolution of eukaryotes
  • #9 Figure 25.2a Exploring the early evolution of eukaryotes (part 1: initial diversification)
  • #10 Figure 25.2aa Exploring the early evolution of eukaryotes (part 1a: early eukaryote fossil)
  • #11 Figure 25.2ab Exploring the early evolution of eukaryotes (part 1b: Tappania)
  • #12 Figure 25.2b Exploring the early evolution of eukaryotes (part 2: appearance of novel features)
  • #13 Figure 25.2ba Exploring the early evolution of eukaryotes (part 2a: Bangiomorpha)
  • #14 Figure 25.2bb Exploring the early evolution of eukaryotes (part 2b: Proterocladus)
  • #15 Figure 25.2bc Exploring the early evolution of eukaryotes (part 2c: Bonneia)
  • #16 Figure 25.2c Exploring the early evolution of eukaryotes (part 3: rise of large eukaryotes)
  • #17 Figure 25.2ca Exploring the early evolution of eukaryotes (part 3a: Doushantuophyton)
  • #18 Figure 25.2cb Exploring the early evolution of eukaryotes (part 3b: Spriggina floundersi)
  • #21 Table 25.1 Inferred origins of key eukaryotic features
  • #25 Figure 25.3 A hypothesis for the origin of eukaryotes through endosymbiosis
  • #30 Figure 25.4 Diversity of plastids produced by endosymbiosis
  • #31 Figure 25.4a Diversity of plastids produced by endosymbiosis (part 1: primary endosymbiosis)
  • #32 Figure 25.4b Diversity of plastids produced by endosymbiosis (part 2: endosymbiosis of red algae)
  • #33 Figure 25.4c Diversity of plastids produced by endosymbiosis (part 3: endosymbiosis of green algae)
  • #37 Figure 25.5 Pediastrum
  • #40 Figure 25.6 Morphological change in the Volvox lineage
  • #43 Figure 25.7 Three lines of evidence that choanoflagellates are closely related to animals
  • #45 Figure 25.8 Cadherin proteins in choanoflagellates and animals
  • #50 Figure 25.9 Exploring eukaryotic diversity
  • #51 Figure 25.9a Exploring eukaryotic diversity (part 1: phylogenetic hypothesis of eukaryotic supergroups)
  • #52 Figure 25.9aa Exploring eukaryotic diversity (part 1a: phylogenetic hypothesis of eukaryotic supergroups)
  • #53 Figure 25.9ab Exploring eukaryotic diversity (part 1b: phylogenetic hypothesis of eukaryotic supergroups)
  • #54 Figure 25.9b Exploring eukaryotic diversity (part 2: micrographs)
  • #55 Figure 25.9ba Exploring eukaryotic diversity (part 2a: Excavata, SEM)
  • #56 Figure 25.9bb Exploring eukaryotic diversity (part 2b: SAR clade, Stramenopila, LM)
  • #57 Figure 25.9bc Exploring eukaryotic diversity (part 2c: SAR clade, Rhizaria)
  • #58 Figure 25.9bca Exploring eukaryotic diversity (part 2ca: SAR clade, Rhizaria, foram, LM)
  • #59 Figure 25.9bcb Exploring eukaryotic diversity (part 2cb: SAR clade, Rhizaria, foram test)
  • #60 Figure 25.9bd Exploring eukaryotic diversity (part 2d: Archaeplastida)
  • #61 Figure 25.9bda Exploring eukaryotic diversity (part 2da: Archaeplastida, Volvox containing “daughter” algae, LM)
  • #62 Figure 25.9bdb Exploring eukaryotic diversity (part 2db: Archaeplastida, Volvox wall, LM)
  • #63 Figure 25.9be Exploring eukaryotic diversity (part 2e: Unikonta)
  • #65 Figure 25.UN02 In-text figure, Excavata, p. 492
  • #68 Figure 25.10 The parabasalid parasite, Trichomonas vaginalis (colorized SEM)
  • #70 Figure 25.11 Euglenozoan flagellum
  • #71 Figure 25.11a Euglenozoan flagellum (part 1: TEM)
  • #74 Figure 25.12 Trypanosoma, the kinetoplastid that causes sleeping sickness
  • #76 Figure 25.UN03 In-text figure, the SAR clade, p. 493
  • #78 Figure 25.13 The diatom Triceratium morlandii (colorized SEM)
  • #81 Figure 25.14 Seaweeds: adapted to life at the ocean’s margins
  • #83 Figure 25.15 Alveoli
  • #84 Figure 25.15a Alveoli (TEM)
  • #86 Figure 25.16 Pfiesteria shumwayae, a dinoflagellate
  • #88 Figure 25.17 Structure and function in the ciliate Paramecium caudatum
  • #89 Figure 25.17a Structure and function in the ciliate Paramecium caudatum (LM)
  • #94 Figure 25.18 A second case of primary endosymbiosis?
  • #96 Figure 25.UN04 In-text figure, Archaeplastida, p. 495
  • #98 Figure 25.19 Red algae
  • #99 Figure 25.19a Red algae (part 1: Bonnemaisonia hamifera)
  • #100 Figure 25.19b Red algae (part 2: nori growing on nets)
  • #101 Figure 25.19c Red algae (part 3: nori in sushi)
  • #104 Figure 25.20 Multicellular chlorophytes
  • #105 Figure 25.20a Multicellular chlorophytes (part 1: sea lettuce)
  • #106 Figure 25.20b Multicellular chlorophytes (part 2: Caulerpa)
  • #108 Figure 25.UN05 In-text figure, Unikonta, p. 496
  • #109 Figure 25.21 Inquiry: Where is the root of the eukaryotic tree?
  • #113 Figure 25.22 The life cycle of Dictyostelium, a cellular slime mold
  • #114 Figure 25.22a-1 The life cycle of Dictyostelium, a cellular slime mold (part 1, step 1)
  • #115 Figure 25.22a-2 The life cycle of Dictyostelium, a cellular slime mold (part 1, step 2)
  • #116 Figure 25.22a-3 The life cycle of Dictyostelium, a cellular slime mold (part 1, step 3)
  • #117 Figure 25.22a-4 The life cycle of Dictyostelium, a cellular slime mold (part 1, step 4)
  • #118 Figure 25.22a-5 The life cycle of Dictyostelium, a cellular slime mold (part 1, step 5)
  • #119 Figure 25.22b The life cycle of Dictyostelium, a cellular slime mold (part 2: aggregate)
  • #120 Figure 25.22c The life cycle of Dictyostelium, a cellular slime mold (part 3: fruiting body)
  • #127 Figure 25.23 Protists: key producers in aquatic communities
  • #131 Figure 25.24 Effects of climate change on marine producers
  • #132 Figure 25.24a Effects of climate change on marine producers (part 1: changes in SST)
  • #133 Figure 25.24b Effects of climate change on marine producers (part 2: changes in chlorophyll concentration)
  • #135 Figure 25.25 A symbiotic protist
  • #142 Figure 25.26 The two-host life cycle of Plasmodium, the apicomplexan that causes malaria
  • #143 Figure 25.26a The two-host life cycle of Plasmodium, the apicomplexan that causes malaria (TEM)
  • #144 Figure 25.UN01 Skills exercise: interpreting comparisons of genetic sequences
  • #145 Figure 25.UN06 Summary of key concepts: supergroups