BIO Ch. 28
SAR
Names after three large and diverse clades -Stramenopiles -Alveolates -Rhizarians
SAR: Alveolates: Apicomplexans
Nearly all apicomplexans are parasites of animals The parasites spread through their host as tiny infectious cells called sporozoites. Apicomplexans are so named because one end (the apex) of the sporozoite cell contains a complex of organelles specialized for penetrating host cells and tissues. Although apicomplexans are not photosynthetic, recent data show that they retain a modified plastid (apicoplast), most likely of red algal origin. plasmodium (malaria) Complex life cycles sometime requiring two organisms
What evidence indicates that the excavates form a clade?
Unique cytoskeletal features are shared by many excavates. In addition, some members of Excavata have an "excavated" feeding groove for which the group was named. Moreover, recent genomic studies support the monophyly of the excavate supergroup.
Excavata
diplomonads, parabasalids, euglenozoans -Excavated groove on one side of the cell body (giardia)
Unikinonta
extremely diverse supergroup of eukaryotes that includes animals, fungi, and some protists two major clades of unikonts, the amoebozoans (tubulinids and close protist relatives) and the opisthokonts (animals, fungi, and closely related protist groups)
Unikonta: [Amoebozoans]: Slime Molds: Plasmodial Slime Molds
form a mass called a plasmodium, which can be many centimeters in diameter Despite its size, the plasmodium is not multicellular; it is a single mass of cytoplasm that is undivided by plasma membranes and that contains many nuclei; product of mitotic nuclear divisions that are not followed by cytokinesis the plasmodium stops growing and differentiates into fruiting bodies that function in sexual reproduction
SAR: Rhizarians: Radiolarians
have delicate, intricately symmetrical internal skeletons that are generally made of silica The pseudopodia of these mostly marine protists radiate from the central body
Photosynthetic protists
convert CO2CO2 to organic compounds Producers form the base of ecological food webs. In aquatic communities, the main producers are photosynthetic protists and prokaryotes Scientists estimate that roughly 30% of the world's photosynthesis is performed by diatoms, dinoflagellates, multicellular algae, and other aquatic protists. Photosynthetic prokaryotes contribute another 20%, and plants are responsible for the remaining 50%.
Archaeplastids, which include land plants and red and green algae, are thought to have descended from a heterotrophic protist that engulfed a(n) __________.
cyanobacterium
Alga
(plural, Algae) A general term for any species of photosynthetic protist, including both unicellular and multicellular forms. Algal species are included in three eukaryote supergroups (Excavata, SAR, Archeaplastida)
Excavata: Parabasalids
-Also have reduced mitochondria; called hydrogenosomes. These organelles generate some energy anaerobically, releasing hydrogen gas as a by-product. - Trichomonas vaginalis
Excavata: Diplomonads + Parabasalids
-Lack plastids and have highly reduced mitochondria -Most diplomonads and parabasalids are found in anaerobic environments.
Excavata: Diplomonads
-Reduced mitochondria called mitosomes - No electron transport chain, cant use oxygen to extract energy from carbs, instead use anaerobic biochemical pathways to get energy instead. -Two nuclei and multiple flagella
Excavata: Euglenazoans
-includes predatory heterotrophs, photosynthetic autotrophs, mixotrophs, and parasites -The main morphological feature that distinguishes protists in this clade is the presence of a rod with either a spiral or a crystalline structure inside each of their flagella -kinetoplastids and the euglenids
Larger size and greater complexity evolved in green algae by three different mechanisms
1. The formation of colonies of individual cells, as seen in Pediastrum (Figure 28.24a) and other species that contribute to the stringy masses known as pond scum. 2. The formation of true multicellular bodies by cell division and differentiation, as in Volvox (see Figure 28.5) and Ulva (Figure 28.24b). 3. The repeated division of nuclei with no cytoplasmic division, as in Caulerpa (Figure 28.24c).
Excavata: Euglenzoans: Euglenids
A euglenid has a pocket at one end of the cell from which one or two flagella emerge (Figure 28.10). Some euglenids are mixotrophs: They perform photosynthesis when sunlight is available, but when it is not, they can become heterotrophic, absorbing organic nutrients from their environment.
Unikonta
Also called amorphea, includes amoebas that have lobe, or tube shaped pseudopodia, as well as animals, fungi, and non-amoeba protists that are closely related to animals and fungi. According to one hypothesis, were the first to diverge from all of Eukaryotes.
SAR: Stramenopiles: Brown Algae
All are multicellular, and most are marine. Brown algae are especially common along temperate coasts that have cold-water currents. They owe their characteristic brown or olive color to the carotenoids in their plastids Many of the species commonly called "seaweeds" are brown algae
Contrast the pseudopodia of amoebozoans and forams.
Amoebozoans have lobe- or tube-shaped pseudopodia, whereas forams have threadlike pseudopodia.
Protist
An informal term applied to any eukaryote that is not a plant, animal, or fungus. Most protists are unicellular, though some are colonial or multicellular. -The organisms in most eukaryotic lineages are protists, and -Most protists are unicellular
Archeaplastida
Archaeplastida is a monophyletic group that descended from the ancient protist that engulfed a cyanobacterium. red algae, green algae, land plants
Justify the claim that photosynthetic protists are among the biosphere's most important organisms.
Because photosynthetic protists constitute the base of aquatic food webs, many aquatic organisms depend on them for food, either directly or indirectly. (In addition, a substantial percentage of the oxygen produced by photosynthesis is made by photosynthetic protists.)
SAR: Alveolates: Dinoflagellates
Cells of many dinoflagellates are reinforced by cellulose plates. Grooves in this "armor" house two flagella, one of which causes dinoflagellates (from the Greek dinos, whirling) to spin as they move through the waters of their marine and freshwater communities red tide
Common ancestor of Mitochondria
Collectively, such studies indicate that mitochondria arose from an alpha proteobacterium (see Figure 27.17). Results from mtDNA sequence analyses also indicate that the mitochondria of protists, animals, fungi, and plants descended from a single common ancestor, thus suggesting that mitochondria arose only once over the course of evolution. Similar analyses provide evidence that plastids descended from a single common ancestor—a cyanobacterium that was engulfed by a eukaryotic host cell.
Conjugation in ciliates is...
Conjugation in ciliates is sexual, resulting in the production of two genetically novel individuals combining the genes of two parents. It is not reproduction, because no additional individuals are produced, although it is followed by reproduction. Read about ciliates.
WHAT IF? High water temperatures and pollution can cause corals to expel their dinoflagellate symbionts. How might such "coral bleaching" affect corals and other species?
Corals depend on their dinoflagellate symbionts for nourishment, so coral bleaching could cause the corals to die. As the corals die, less food would be available for fishes and other species that eat coral. As a result, populations of these species might decline, and that, in turn, might cause populations of their predators to decline.
Review Figures 9.2 and 10.5, and then summarize how CO2CO2 and O2O2 are both used and produced by chlorarachniophytes and other aerobic algae.
During photosynthesis, aerobic algae produce O2O2 and use CO2CO2. O2O2 is produced as a by-product of the light reactions, while CO2CO2 is used as an input to the Calvin cycle (the end products of which are sugars). Aerobic algae also perform cellular respiration, which uses O2O2 as an input and produces CO2CO2 as a waste product.
Four supergroups of Eukaryotes
Excavata, SAR, Archaeplastida, Unikonta
True or false? Organisms that exhibit alternation of generations reproduce sexually in the diploid stage.
False. Organisms that exhibit alternation of generations reproduce asexually in the diploid stage by producing haploid cells that form spores, which then germinate into haploid adults. The haploid adults produce haploid gametes that can then participate in sexual reproduction.
After studying Figure 28.3, predict how many distinct genomes are contained within the cell of a chlorarachniophyte. Explain.
Four. The first (and primary) genome is the DNA located in the chlorarachniophyte nucleus. A chlorarachniophyte also contain remnants of a green alga's nuclear DNA, located in the nucleomorph. Finally, mitochondria and chloroplasts contain DNA from the (different) bacteria from which they evolved. These two prokaryotic genomes comprise the third and fourth genomes contained within a chlorarachniophyte.
Archaeplastida: Green Algae (paraphyletic group)
Green algae can be divided into two main groups, the charophytes and the chlorophytes. The charophytes include the algae most closely related to plants
Difference between multicellular organisms and unicellular protists?
In multicellular organisms, essential biological functions are carried out by organs. Unicellular protists carry out the same essential functions, but they do so using subcellular organelles, not multicellular organs. The organelles that protists use are mostly those discussed in Figure 6.8, including the nucleus, endoplasmic reticulum, Golgi apparatus, and lysosomes.
Symbiotic Protists
Many protists form symbiotic associations with other species photosynthetic dinoflagellates are food-providing symbiotic partners of the animals (coral polyps) that build coral reefs wood-digesting protists that inhabit the gut of many termite species
Contrast red algae and brown algae.
Many red algae contain a photosynthetic pigment called phycoerythrin, which gives them a reddish color and allows them to carry out photosynthesis in relatively deep coastal water. Also unlike brown algae, red algae have no flagellated stages in their life cycle and must depend on water currents to bring gametes together for fertilization.
SAR: Rhizarians
Many species in this group are amoebas, protists that move and feed by means of pseudopodia, extensions that may bulge from almost anywhere on the cell surface Most amoebas that are rhizarians differ morphologically from other amoebas by having threadlike pseudopodia. Rhizarians also include flagellated (non-amoeboid) protists that feed using threadlike pseudopodia radiolarians, forams, and cercozoans.
Evidence for secondary Endosymbiosis
On several occasions during eukaryotic evolution, red algae and green algae underwent secondary endosymbiosis, meaning they were ingested in the food vacuoles of heterotrophic eukaryotes and became endosymbionts themselves. For example, protists known as chlorarachniophytes likely evolved when a heterotrophic eukaryote engulfed a green alga. Evidence for this process can be found within the engulfed cell, which contains a tiny vestigial nucleus, called a nucleomorph (Figure 28.4). Genes from the nucleomorph are still transcribed, and their DNA sequences indicate that the engulfed cell was a green alga.
Archaeplastida
One of the five supergroups of eukaryotes. It includes red algae, green algae, and land plants, descended from an ancient protist ancestor that engulfed a cyanobacterium. -contains key photosynthetic species that form the base of the food web in many aquatic communities Volvox
SAR: Stramenopiles: Oomycetes
Oomycetes include the water molds, the white rusts, and the downy mildews. previously classified as fungi many oomycetes have multinucleate filaments (hyphae) that resemble fungal hyphae oomycetes typically have cell walls made of cellulose, whereas the walls of fungi consist mainly of another polysaccharide, chitin.
Unikonta: [Opisthokonts]
Opisthokonts are an extremely diverse group of eukaryotes that includes animals, fungi, and several groups of protists. The nucleariids and choanoflagellates illustrate why scientists have abandoned the former kingdom Protista: A monophyletic group that includes these single-celled eukaryotes would also have to include the multicellular animals and fungi that are closely related to them
Describe three symbioses that include protists.
Protists form mutualistic and parasitic associations with other organisms. Examples include photosynthetic dinoflagellates that form a mutualistic symbiosis with coral polyps; parabasalids that form a mutualistic symbiosis with termites; and the stramenopile Phytophthora ramorum, a parasite of oak trees.
Cite at least four examples of structural and functional diversity among protists
Protists include unicellular, colonial, and multicellular organisms; photoautotrophs, heterotrophs, and mixotrophs; species that reproduce asexually, sexually, or both ways; and organisms with diverse physical forms and adaptations.
Describe similarities and differences between protists and other eukaryotes.
Protists, plants, animals, and fungi are similar in that their cells have a nucleus and other membrane-enclosed organelles, unlike the cells of prokaryotes. These membrane-enclosed organelles make the cells of eukaryotes more complex than the cells of prokaryotes. Protists and other eukaryotes also differ from prokaryotes in having a well-developed cytoskeleton that enables them to have asymmetric forms and to change in shape as they feed, move, or grow. With respect to differences between protists and other eukaryotes, most protists are unicellular, unlike animals, plants, and most fungi. Protists also have greater nutritional diversity than other eukaryotes.
Archeaplastida: Red Algae
Red algae are abundant in the warm coastal waters of tropical oceans many are reddish, owing to the photosynthetic pigment phycoerythrin, which masks the green of chlorophyll their photosynthetic pigments, including phycoerythrin, allow them to absorb blue and green light, which penetrate relatively far into the water Most red algae are multicellular. Although none are as big as the giant brown kelps Red algae reproduce sexually and have diverse life cycles in which alternation of generations is common. However, unlike other algae, red algae do not have flagellated gametes, so they depend on water currents to bring gametes together for fertilization.
Suggest a possible reason why species in the green algal lineage may have been more likely to colonize land than species in the red algal lineage.
Red algae have no flagellated stages in their life cycle and hence must depend on water currents to bring their gametes together. This feature of their biology might increase the difficulty of reproducing on land. In contrast, the gametes of green algae are flagellated, making it possible for them to swim in thin films of water. In addition, a variety of green algae contain compounds in their cytoplasm, cell wall, or zygote coat that protect against intense sunlight and other terrestrial conditions. Such compounds may have increased the chance that descendants of green algae could survive on land.
On what basis do systematists place plants in the same supergroup (Archaeplastida) as red and green algae?
Red algae, green algae, and plants are placed in the same supergroup because considerable evidence indicates that these organisms all descended from the same ancestor, an ancient heterotrophic protist that acquired a cyanobacterial endosymbiont.
Heteromorphic
Referring to a condition in the life cycle of plants and certain algae in which the sporophyte and gametophyte generations differ in morphology.
Isomorphic
Referring to alternating generations in plants and certain algae in which the sporophytes and gametophytes look alike, although they differ in chromosome number.
eukaryotic supergroup to which ciliates belong
SAR
Describe several protists that are ecologically important.
Sample response: Ecologically important protists include photosynthetic dinoflagellates that provide essential sources of energy to their symbiotic partners, the corals that build coral reefs. Other important protistan symbionts include those that enable termites to digest wood and Plasmodium, the pathogen that causes malaria. Photosynthetic protists such as diatoms are among the most important producers in aquatic communities; as such, many other species in aquatic environments depend on them for food.
DNA sequence data for a diplomonad, a euglenid, a plant, and an unidentified protist suggest that the unidentified species is most closely related to the diplomonad. Further studies reveal that the unknown species has fully functional mitochondria. Based on these data, at what point on the phylogenetic tree in Figure 28.5 did the mystery protist's lineage probably diverge from other eukaryote lineages? Explain.
Since the unknown protist is more closely related to diplomonads than to euglenids, it must have originated after the lineage leading to the diplomonads and parabasalids diverged from the euglenozoans. In addition, since the unknown species has fully functional mitochondria—yet both diplomonads and parabasalids do not—it is likely that the unknown species originated before the last common ancestor of the diplomonads and parabasalids.
In what sense is "fungus animal" a fitting description of a slime mold? In what sense is it not fitting?
Slime molds are fungus-like in that they produce fruiting bodies that aid in the dispersal of spores, and they are animal-like in that they are motile and ingest food. However, slime molds are more closely related to tubulinids and entamoebas than to fungi or animals.
Unikonta: [Amoebozoans]: Slime Molds
Slime molds, or mycetozoans (from the Latin, meaning "fungus animals"), once were thought to be fungi because, like fungi, they produce fruiting bodies that aid in spore dispersal Slime molds have diverged into two main branches, plasmodial slime molds and cellular slime molds
Protist nutrition
Some protists are photoautotrophs and contain chloroplasts. Some are heterotrophs, absorbing organic molecules or ingesting larger food particles. Still other protists, called mixotrophs, combine photosynthesis and heterotrophic nutrition. Photoautotrophy, heterotrophy, and mixotrophy have all arisen independently in many different protist lineages.
Summarize the role of endosymbiosis in eukaryotic evolution.
Strong evidence shows that eukaryotes acquired mitochondria after a host cell (either an archaean or a cell closely related to the archaea) first engulfed and then formed an endosymbiotic association with an alpha proteobacterium. Similarly, chloroplasts in red and green algae appear to have descended from a photosynthetic cyanobacterium that was engulfed by an ancient heterotrophic eukaryote. Secondary endosymbiosis also played an important role: Various protistan lineages acquired plastids by engulfing unicellular red or green algae.
SAR: Alveolates
The alveolates, have membrane-enclosed sacs (alveoli) just under the plasma membrane consists of flagellates (the dinoflagellates), a group of parasites (the apicomplexans), and a group of protists that move using cilia (the ciliates)
Unikonta: [Amoebozoans]
The amoebozoan clade includes many species of amoebas that have lobe- or tube-shaped pseudopodia rather than the threadlike pseudopodia found in rhizarians. Amoebozoans include tubulinids, slime molds, and entamoebas.
Unikonta: [Amoebozoans]: Slime Molds: Cellular Slime Molds
The feeding stage of these organisms consists of solitary cells that function individually, but when food is depleted, the cells form a slug-like aggregate that functions as a unit (Figure 28.28). Unlike the feeding stage (plasmodium) of a plasmodial slime mold, these aggregated cells remain separated by their individual plasma membranes. Ultimately, the aggregated cells form an asexual fruiting body
Alpha proteobacteria were used as the outgroup to estimate the tree shown in Figure 28.26. Explain why these bacteria were selected as the outgroup rather than other bacterial or archaeal lineages. (See Figure 26.12 and associated text in Concept 26.3.)
The genes used to estimate the tree shown in Figure 28.26 were transferred from an alpha proteobacterium to an early eukaryote. Based on the sequences of these genes, the eukaryotes should be more closely related to alpha proteobacteria than they are to any other lineage of prokaryotes. Thus, alpha proteobacteria are well suited as an outgroup to the eukaryotes (the group of species whose relationships we are trying to determine).
Would you expect the plastid DNA of photosynthetic dinoflagellates and diatoms to be more similar to the nuclear DNA of plants (domain Eukarya) or to the chromosomal DNA of cyanobacteria (domain Bacteria)? Explain
The plastid DNA would likely be more similar to the chromosomal DNA of cyanobacteria based on the well-supported hypothesis that eukaryotic plastids (such as those found in the eukaryotic groups listed) originated by an endosymbiosis event in which a eukaryote engulfed a cyanobacterium. If the plastid is derived from the cyanobacterium, its DNA would be derived from the bacterial DNA.
Archaeplastida: Chlorophytes
The second group, the chlorophytes (from the Greek chloros, green), includes more than 7,000 species. Most live in fresh water, but there are also many marine and some terrestrial species. The simplest chlorophytes are unicellular organisms such as Chlamydomonas, which resemble gametes of more complex chlorophytes. Various species of unicellular chlorophytes live independently in aquatic habitats as phytoplankton or inhabit damp soil Some live symbiotically within other eukaryotes, contributing part of their photosynthetic output to the food supply of their hosts Nearly all species of chlorophytes reproduce sexually by means of biflagellated gametes that have cup-shaped chloroplasts (Figure 28.25). Alternation of generations has evolved in some chlorophytes, including Ulva.
The bacterium Wolbachia is a symbiont that lives in mosquito cells and spreads rapidly through mosquito populations. Wolbachia can make mosquitoes resistant to infection by Plasmodium; researchers are seeking a strain that confers resistance and does not harm mosquitoes. Compare evolutionary changes that could occur if malaria control is attempted using such a Wolbachia strain versus using insecticides to kill mosquitoes. (Review Figure 28.18 and Concept 23.4.)
The two approaches differ in the evolutionary changes they may bring about. A strain of Wolbachia that confers resistance to infection by Plasmodium and does not harm mosquitoes would spread rapidly through the mosquito population. In this case, natural selection would favor any Plasmodium individuals that could overcome the resistance to infection conferred by Wolbachia. If insecticides are used, mosquitoes that are resistant to the insecticide would be favored by natural selection. Hence, use of Wolbachia could cause evolution in Plasmodium populations, while using insecticides could cause evolution in mosquito populations.
Describe a key feature for each of the main protist subgroups of Unikonta.
The unikonts are a diverse group of eukaryotes that includes many protists, along with animals and fungi. Most of the protists in Unikonta are amoebozoans, a clade of amoebas that have lobe- or tube-shaped pseudopodia (as opposed to the threadlike pseudopodia of rhizarians). Other protists in Unikonta include several groups that are closely related to fungi and several other groups that are closely related to animals.
Why do some biologists describe the mitochondria of diplomonads and parabasalids as "highly reduced"?
Their mitochondria do not have an electron transport chain and so cannot function in aerobic respiration.
SAR: Stremenopiles
Their name (from the Latin stramen, straw, and pilos, hair) refers to their characteristic flagellum, which has numerous fine, hairlike projections. In most stramenopiles, this "hairy" flagellum is paired with a shorter "smooth" (nonhairy) flagellum diatoms, oomycetes, and brown algae.
Unikonta: [Amoebozoans]: Entamoebas
Whereas most amoebozoans are free-living, those that belong to the genus Entamoeba are symbiotic parasites They infect all classes of vertebrate animals as well as some invertebrates. E. histolytica causes amoebic dysentery and is spread via contaminated drinking water, food, or eating utensils. Responsible for up to 110,000 deaths worldwide every year, the disease is the third-leading cause of death due to eukaryotic parasites, after malaria (see Figure 28.18) and schistosomiasis
secondary endosymbiosis
a process in eukaryotic evolution in which a heterotrophic eukaryotic cell engulfed a photosynthetic eukaryotic cell which survived in a symbiotic relationship inside the heterotrophic cell
Biologists think that endosymbiosis gave rise to mitochondria before plastids partly because
all eukaryotes have mitochondria (or their remnants), whereas many eukaryotes do not have plastids.
SAR: Alveolates: Ciliates
large and varied group of protists named for their use of cilia to move and feed (Figure 28.19a). Most ciliates are predators, typically of bacteria or of other protists. Their cilia may completely cover the cell surface or may be clustered in a few rows or tufts. In certain species, rows of tightly packed cilia function collectively in locomotion. Other ciliates scurry about on leg-like structures constructed from many cilia bonded together
SAR: Rhizarians: Cercozoans
large group of amoeboid and flagellated protists that feed using threadlike pseudopodia Most cercozoans are heterotrophs. Many are parasites of plants, animals, or other protists; many others are predators. The predators include the most important consumers of bacteria in aquatic and soil ecosystems, along with species that eat other protists, fungi, and even small animals chlorarachniophytes (mentioned earlier in the discussion of secondary endosymbiosis), are mixotrophic: These organisms ingest smaller protists and bacteria as well as perform photosynthesis
How did plastids arise?
morphological and molecular evidence indicates that plastids arose when a heterotrophic protist acquired a cyanobacterial endosymbiont. Later, photosynthetic descendants of this ancient protist evolved into red algae and green algae (see Figure 28.3), and the lineage that produced green algae then gave rise to plants.
SAR: Rhizarians: Forams
named for their porous shells, called tests Foram tests consist of a single piece of organic material that typically is hardened with calcium carbonate. The pseudopodia that extend through the pores function in swimming, test formation, and feeding. Many forams also derive nourishment from the photosynthesis of symbiotic algae that live within the tests. ocean and fresh water. Most species live in sand or attach themselves to rocks or algae, but some live as plankton. The largest forams, though single-celled, have tests several centimeters in diameter
Excavata: Euglenazoans: Kintetoplastids
single, large mitochondrion that contains an organized mass of DNA called a kinetoplast trypanosomes change syrface protein to fool host immune system
Endosymbiosis in Eukaryotic Evolution
structural, biochemical, and DNA sequence data indicate that mitochondria and plastids are derived from bacteria that were engulfed by the ancestors of early eukaryotic cells. The evidence also suggests that mitochondria evolved before plastids. Thus, a defining moment in the origin of eukaryotes occurred when a host cell engulfed a bacterium that would later become an organelle found in all eukaryotes—the mitochondrion.
SAR: Stramenopiles: Diatoms
unicellular algae that have a unique glass-like wall made of silicon dioxide embedded in an organic matrix -shoebox structure with lid -walls provide effective protection from the crushing jaws of predators -CO2 absorbed by diatoms during photosynthesis is transported, or "pumped," to the ocean floor
Unikonta: [Amoebozoans]: Tubulinids
unicellular protists are ubiquitous in soil as well as freshwater and marine environments. Most are heterotrophs that actively seek and consume bacteria and other protists; one such tubulinid species, Amoeba proteus, is shown in Figure 28.5. Some tubulinids also feed on detritus (nonliving organic matter).