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Q When these two protists meet, who is the prey? Although they are both protists, the round Didinium hunts live paramecia almost exclusively. Paramecia are much longer than this predator, but that doesn’t stop Didinium. It captures, paralyzes, and reels in paramecia like fish on a line. It then eats its prey whole, expanding its own body just so that its meal will fit.

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r e a d i N G T o o lb o x This reading tool can help you learn the material in the following pages.

USING LANGUAGE Your Turn General Statements A general statement summa- Use what you know about general statements to answer rizes the features of a group or describes an average the following questions. feature of the members of the group. Some individuals in 1. Write a general statement that summarizes the the group may not share all of the features. So, general features of baseballs, basketballs, tennis balls, soccer statements may be true most of the time, but not always. balls, and footballs. 2. Brainstorm exceptions to the general statement “In general, dogs have four legs, fur, and a tail and can bark.”

Chapter 19: Protists and Fungi 555 CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info” Unit 556 this section. of protists mentionedin take notes aboutthegroups Use athree-column to chart T protist VOCABULARY using ahierarchic animals bacteria, protists, fungi,plants, and taxonomic groups, including archaea, and 8 differences shared amonggroups system based onsimilarities and animal-like AKI ru ecito Examples Description Group R E N C

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Classification andDiversity B N categorize organisms 19.1 O N TE G e characteristics of S al classification TO 8b, 8c B L O o Diversity ofProtists x ki or funguslike.or Protists cananimal-like, be plantlike, can bequite complex. ing—they can carry outall life withinjustonecell. functions Asyou see, will onecell appearances, they are single-celled. That is what makes single-celled protists so amaz- might findspecimensofboth DidiniumandParamecium . Despite theirunique If you looked at adrop ofwater from apond,roadside puddle, orabird bath, you Your to World Connect Ke ngdoms. ngdoms.

y A of phyla. Members of kingdom this are often simply protists. called inkingdomclassified Protista, diverse kingdom avery that includes hundreds but are they unusual. Slime molds are one ofgroups several of living things dog vomit. mold of because its resemblance to—well, commonlya species dog-vomit called slime it was Fuligo septica, shown inFIGURE1.1, lifealien form, but aslime mold. Specifically, onseeing sunny this day in1973wasn’t an neighborhood werepeople Dallas inthe only made invaders the grow. turned on hoses their blobs, the but water andpolice firefighters. The firefighters residents neighborhood called of aDallas Afraid that was this an invasion, alien lawns and pulsing up telephone poles. out of nowhere. were They spreading across Large yellow globsof to slime come seemed ally, whereas others reproduce and asexually sexually. both around and responding to environment. the Some protists reproduce asexu- multicellular, microscopic large. or very have They different ways of moving inanythem of three kingdoms. these Protists may or single-celled be animals, plants, lack and one also fungi, they or more traits that would place generally grouped together because, share although they some features with MAI MAI C Protists Protists protist o Slime m Scie N n N ID c ID ntists came to rescue. the What the e p E E

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to members of other kingdoms than to other protists. most are only distantly related. In many fact, protists are more closely related includes many phyla. phyla These are different very from one another, and Animalia, Fungi,Eukarya: Plantae, and Protista. The kingdom Protista otes inone domain, There Eukarya. are four kingdoms within domain the prokaryotes into two domains, Archaea and and eukary- places Bacteria, all You have that learned three-domain the system of classification divides convenient way to study diversity. their evolutionaryreflect relationships, but it is a Categorizingfood. protists way inthis not does br doms, term protist the remains studying when useful group. the there is awidely accepted division of kingdom Protista into multiple king- than 15kingdoms of eukaryotes rather than four the we currently use. Until animals were as aguide for used classifying protists, we’d end up with more domain If Eukarya. genetic the differences to fungi, plants, classify used and protist kingdom eventually will divided into be kingdoms several within the genetic relationships groups between of organisms, many biologists the think definitions.fungi Now that techniques molecular biology have the revealed a kingdom for eukaryotes the that all don’t to fit animal, the seem plant, or Animal-like • Funguslike • Plantlike • MAI oad categoriesoad on how based get their they Protists divided informally can be into three Kingdom Protista considered can be junk-drawer the of kingdoms. the It is such as Euplotes the in cannot. You about learn will later fungi chapter. inthis protists can move during of part life their cycle, whereas fungi were once inkingdom classified Fungi. However, funguslike decompose organisms. dead of trait, this Because protists these celled, colonial, or multicellular. plants are multicellular, plantlike protists may either be single- plasts, do not they have roots, stems, or leaves. all And while Although protists these may have chloro- own by food photosynthesis just as plants do. Pediastrum algae the in matter how simple—are multicellular. are animals—no all single-celled, while organisms. However, animal-like all protists ero

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FIGURE 1.3 Relationships of Protists to Other Eukaryotes All protists currently belong to kingdom Protista, but some protists are more closely related to other kingdoms than to members of their own kingdom. a ae tists Fungi

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This proposed phylogenetic tree illustrates the diversity of protists. For example, slime molds are more closely related to fungi and ancestor animals than they are to other protists.

You can see the genetic relationship of protists to each other and to other kingdoms in FIGURE 1.3. For example, a comparison of RNA sequences between plants and green algae indicates that green algae are more closely related to plants than to other algae. Protist classification is a very active area of research, and in the future may provide insight into areas of study such as preventing or treating protist-caused diseases. Summarize What is the argument for placing protists in more than one kingdom? 8b, 8c

Self-check Online HMDScience.com 19.1 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. Name the three main groups within 3. Infer What observable traits might Ecology the kingdom Protista. What charac- green algae and plants share that 5. Organisms that get their teristics distinguish each group from support the molecular evidence that food by ingesting it are called the other two? 8b, 8c these two groups are closely related? heterotrophs, while those 2. Give two reasons why protists are 8c that make their own food are difficult to classify. 8B, 8c 4. Contrast At one time, scientists called autotrophs. Categorize grouped all single-celled organisms animal-like, plantlike, and together. What are the main differ- funguslike protists using ences between single-celled protists these two terms. 8b and bacteria or archaea? 8c

558 Unit 6: Classification and Diversity CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info”

©Photo Researchers, Inc. FIGURE 2.1 FIGURE cilia pseudopod protozoa VOCABULARY cation unknown) cation through fla interpr competition amongorganisms commensalism, mutualism, and predation, parasitism, organisms andecosystems and12 and disrupting thehealth ofboth microorg gella et relationships, including 11

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Animal-like protists move ways. various in th swim. Justlike animals, animal-like protists use different ways to get around. others walk onfour. Somespendmostwhile oftheirtimeflying, others can only Think ofall theways that different animals move. Somewalk ontwo legs, while Your to World Connect Ke

described below.described manythe phyla of animal-like protists. Afew common protozoan groups are both organismsboth benefit. gellates live inside other organisms inmutualism—a relationship inwhich gens, or disease-causing parasites of humans and other animals. Some zoofla- cling nutrients through aquatic ecosystems. zooflagellates Other are patho- onfeed dissolved organic matter, thereby playing an important role inrecy- are heterotrophs. For example, some zooflagellates eat prokaryotes that but prokaryotic are flagella invisible at same the magnification. protists. You protist can easily see with aid the flagella of alight microscope, membrane. Prokaryotic are flagella much also of than smaller flagella the bundles microtubules of tubes small called and are enclosed by plasma the gellate shown inFIGURE2.1,are extensions of cytoplasm. the are They made of ofsurface cell. the In contrast, such of flagella, as those zoofla- the eukaryotic otes, different. are they very structurally Prokaryotic attach flagella to the of zooflagellates (phylum Zoomastigophora) of like look flagella the prokary- tail-like structures that help unicellular organisms Although swim. flagella the one or more at flagella some point that are life intheir cycle.flagella Recall The zooflagellates (zoh-uh-FLAJ-uh-lihts) are animal-like protists that have Protozoa Flagella with mals are multicellular. The term organization:is body their animal-like all protists are unicellular, ani- while lack chloroplasts. The key difference animal-like between protists and animals animals, can move they around, consume they other organisms, and cells their were as classified had animals many they because animal-like traits. Like dom Protista. In early the two-kingdom classification system, some protists The animal-like protists represent largest the number of king- inthe species y at can move. move. can at MAI MAI C Some Animal-like Mor o N n N ID c ID e thanof 2000 species zooflagellates exist.free-living All zooflagellates e

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559 CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info” 560

cel surround extends materials neededby thecell. for thetemporary storage of vacuole sac isafluid-filled used Structure andFunction that a Recall from thechapter Cell Ce 2.2 FIGURE Unit 6:Clas CO l. ll

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cilia all over all cilia surface, their whereas other ciliates just have clusters of cilia. andflagella found inmuch greater numbers. Some ciliates have many rows of help organism the and swim capture are Cilia food. usually much shorter than does notdoes form pseudopods. formation energy. uses When amoeba the is not moving or feeding, it to it surface the is on, and pulls rest the of toward cell the it. Pseudopod cytoplasm flows outward, forming abulge. This bulge spreads, anchors itself membrane that helps protozoa move and feed. To form cell the apseudopod, which means “false foot,” is atemporary extension of cytoplasm and plasma

zooflagellates get and meals free aplace to live. Thewood. termites get nutrition from zooflagellate’s the activity, and the is acomplex community made of zooflagellates and that bacteria can digest Cilia This group’s name, Ciliates, comes from its most obvious feature—cilia. Protozoa Cilia with form to move. pseudopods Rhizopoda) A Amoebas amoebas and foraminifera. the Two groups of protozoa that can easily change shape move as they are the Protozoa Pseudopods with exa Foraminifera without seen can be amicroscope. millimeters indiameter—a huge sizefor organism—and asingle-celled However, Pelomyxa palustris is an amoeba that can grow as large as five are free-living, but some are species parasites. Most amoebas are microscopic. pseudopods to move.pseudopods marine protozoa that, like amoeba, use Foramsspecies. make up alarge group of sand, or other materials, depending on the Their shells are made of organic matter, wordLatin foramen means “little hole.” chambered shell, shown The inFIGURE2.3. forams,called are named for multi- their Foraminifera,uh). sometimes simply Foraminifera (fuh-ram-uh-NIHF-uhr- arewith pseudopods members of phylum and digestion takesplace. Digestive enzymes enter vacuole from food the surrounding the cytoplasm, and outer the membrane of amoeba forms the then vacuole, afood or sac. of solidmaterial by acell. The amoeba surrounds with its food the pseudopod, place by process the of that phagocytosis. phagocytosis Recall is engulfing the An am Sometimes zooflagellates play role acrucial inanother organism’s life. For Amo mple, termites cannot eat. digest they Inside wood the gut the of atermite are short, hairlike structures that cover some or of and surface all cell the ebas live infresh water, salt water, and soil. The majority of amoebas

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About 8000 species of ciliates make up the phylum Figure 2.4 paramecium Ciliophora. Some ciliates are parasites that cause disease. A paramecium is a single-celled However, most ciliates are free-living cells found in fresh protist covered with thousands of water, such as the common pondwater protists in the cilia. Its organelles can be identified genus Paramecium. through its transparent cell membrane. Structures of a paramecium are shown in FIGURE 2.4. Food is swept into the oral groove by the cilia, and is sent to the gullet. Eventually the food is digested in food vacu- oles. Two organs that act like pumps, called contractile macronucleus vacuoles, control the amount of water inside the cell. An unusual trait found in paramecia and other ciliates is the presence of two types of nuclei. Each cell has one contractile food vacuole large macronucleus, but there can be many small micro- vacuole nuclei. The macronucleus controls the cell’s structures oral groove and activities. The micronuclei contain all of the cell’s chromosomes. They function only during conjugation, micronucleus a process of genetic exchange. Two paramecia unite at the oral grooves and exchange micronuclei. Some species cilia of the genus Paramecium have up to 80 micronuclei. Because micronuclei can be exchanged during conjuga- tion, having so many micronuclei allows for a huge amount of genetic variation in paramecia. Summarize What functions do the two kinds of nuclei within Paramecium perform?

colored SEM; magnification 4003 QU I CKLA B observing

Investigating Motion in Protists Materials In this investigation you will observe the movement of one or more of • 4 eyedroppers the following protists: Paramecium, Amoeba, or Euglena. • 4 drops bottled spring water • 3 microscope slides Problem What does a protist’s movement look like? • 2 cover slips 1. Make a wet mount slide of the protist. You may need to add a drop of • culture of Paramecium methylcellulose solution to the wet mount so that you can slow down the • 3 drops methylcellulose organism enough to observe. Caution: Do not use a cover slip on the solution amoeba slide, as you will crush the organism. • culture of Amoeba • culture of Euglena 2. Observe how the organism moves. Make a series of three drawings that • microscope depict the movement of the organism. 3. If time allows, repeat steps 1 and 2 with the other two protists. Analyze and Conclude 1. Analyze Describe the movement of the protist(s) you observed. 2. Analyze What structures did the protist that you observed use to move? 3. Infer Based on the structures you observed, do you think the species of protist that you observed swims in the water or crawls in the bottom sediments? Explain. (cr) ©Eric Grave/Photo Inc. Researchers,

Chapter 19: Protists and Fungi 561 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A

Figure 2.5 Life Cycle of the Malaria Parasite MAIN IDEA 11c, 12a The life cycle of the malaria Some animal-like protists When an infected parasite Plasmodium requires 1 mosquito bites a human, both a mosquito and a cause disease. it transmits Plasmodium human host. sporozoites that enter the Protists cause some of the world’s most well-known liver, where they develop. infectious diseases. The phylum Apicomplexa (a-pih- sporozoites kuhm-plehk-suh) includes about 4000 species, all of which are parasites of animals. Many members of this phylum are known as sporozoans because they human liver form sporozoites—infectious cells that have tough liver outer coats. Malaria is an example of a disease caused cells by sporozoans. It is caused by infection with the protozoan Plasmodium, shown in FIGURE 2.5. Malaria is passed to humans and other animals through the bite of the Anopheles mosquito. Symp- developed parasites toms of malaria include high fever and vomiting. In some cases, the parasite can severely affect kidney red blood and liver function, leading to coma and even death. 3 Some Plasmodium cells cells are ingested by a mos- Although the disease was once on the decline, today quito biting the infected 2 The developed parasites more than 1 million people—mostly children in leave the liver and enter human. The cells repro- developing countries—die from malaria each year. duce in the mosquito’s red blood cells, where stomach and new larvae they reproduce asexu- Mosquitoes have developed resistance to the insecti- develop, which eventually ally until the red blood cides that once would kill them, and Plasmodium cells burst. release sporozoites. species have become resistant to antimalarial drugs. Two other parasitic protists that cause disease are the zooflagellates Trypanosoma and Giardia. In Africa, several species of Trypanosoma cause the disease known as sleeping sickness in humans and Web other mammals. Trypanosomes are transmitted through the bite of the tsetse fly, and can cause coma and death. Giardia causes intestinal disease in hu- HMDScience.com mans. People can become infected with Giardia by drinking water contami- GO ONLINE nated with feces of infected animals. Campers and hikers must be careful of Sickening Protists Giardia, as even streams or rivers that appear clean could be contaminated. Compare How do the parasites Plasmodium and Giardia each infect humans? 11c, 12a Self-check Online HMDScience.com 19.2 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. Name and describe the three basic 3. Compare and Contrast In what ways Analogous means of movement used by animal- are cilia and flagella similar? How are Structures like protists. they different? 5. The flagella of eukaryotes 2. Describe how the parasite Plasmo- 4. Infer Why do amoebas form and prokaryotes serve the dium causes disease in humans. pseudopods only when they same function, but they are 11c, 12a need them? structurally very different. What does this suggest about the evolution of flagella? 8B, 8C

562 Unit 6: Classification and Diversity CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info”

©Roland Birke/Peter Arnold, Inc. algae VOCABULARY organisms andecosystems and disrupting thehealth ofboth microorganisms inboth maintaining using ahierarchic animals; 11 bacteria, protists, fungi,plants, and taxonomic groups, including archaea, 8 differences shared amonggroups; system based onsimilarities and FIGURE 3.1 FIGURE (LM; magnification 50 magnification (LM; colonies Offspring ony that hundreds C compar

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called called owntheir through food photosynthesis. Photosynthetic plantlike protists are other organisms, but most plantlike protists have chloroplasts and can produce Multicellular plantlike protists include seaweeds the or kelps. eat Some species plantlike protists, such as Volvox, shown in ofhalf oxygen the inEarth’s atmosphere. of species single-celled Several that phytoplankton form of base the aquatic chains food and provide about plantlikewhile protists may or single-celled be multicellular. samethe reproductive structures that plants have. plants All are multicellular, plants, plantlike protists do not have roots, stems, tissues, leaves, or specialized plantlike protists like look plants, are they different inmany ways. Unlike that many plantlike protists as classified plants. to be used Although many Just as animal-like protists were once as classified animals, it is not surprising together with photosynthetic are bacteria, known as many generations, colonies could have to led multicellular forms. over time, and eventually may have become dependent on each other. Over gametes. cells These and offspring their would have become more specialized probably efficient at tasks, such very certain as digesting or food producing tosingle-celled multicellular algae, some individual cells incolonies were multicellular forms inwhichcells are the In evolution the specialized. from forms, multicellular independently, acting cell forms with every and Members of order the Volvocales include three kinds of forms: single-celled It is likely that multicellular arose algae from colonies of such algae as Volvox. In distant the past,organisms single-celled combined to become multicellular. toFrom Multicellular Single-Celled y MAI MAI C Many Plantlike Man o N n N ID algae. c ID y single-celled plantlikey single-celled protists are free-living aquatic organisms that, e

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563 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A

Figure 3.2 euglena Diversity of Plantlike Protists Plantlike protists are found in most habitats on Earth. Most A euglena has both animal-like structures—such as an eyespot, contractile vacuoles, and flagella—and are aquatic organisms that live in freshwater and marine ecosys- plantlike structures, such as chloroplasts. tems. Some species live in deserts, while others live in the tundra. Despite their great diversity, plantlike protists have certain features in common, such as the chlorophyll they use for contractile photosynthesis. Also, most plantlike protists have flagella at vacuole some point in their life cycle. Although their classification will pellicle likely change, for now many biologists group the plantlike nucleus flagellum protists into several phyla based on their photosynthetic pig- ments and cell wall structure. chloroplast Euglenoids The euglenoids (phylum Euglenophyta) are a large group of single-celled organisms that swim with the aid of one eye spot or two flagella. Although most of these species are found in fresh water, some live in ocean environments. Members of this group are both animal-like and plantlike. Like animals, these protists can move around easily. Euglenoids have a pellicle, a flexible coatlike covering on their cell surface. The pellicle allows the cell to change shape. In some species, the pellicle helps the organism to creep across solid surfaces using a type of movement that resembles the inching movement of worms. Although some colorless species of euglenoids eat other organisms, most make their own food through photosynthesis. Plantlike photosynthetic euglenoids are green, such as the euglena shown in FIGURE 3.2. Their bright green color comes colored SEM; magnification 1500 from two different chlorophyll pigments, called chlorophyll a and b. Chlorophyll a is found in all photosynthesizing organ- isms. Chlorophyll b is found only in green algae and plants. R E ADI N G TO OLB ox Dinoflagellates The dinoflagellates (phylum Dinoflagellata) are single-celled. About 90 percent of dinoflagellates are marine plankton. Recall that plankton VOCABULARY are often microscopic organisms that live suspended in the water. Some The name dinoflagellates comes from the Greek word dinoflagellates are freshwater species, and a few species have even been found dinos, meaning “whirling,” in snow. About half of all marine dinoflagellates photosynthesize. and the Latin word flagrum, meaning “whip.” This name Dinoflagellates have two flagella. One flagellum extends from the rear of describes how dinoflagellates the cell and propels it forward. The other is a ribbonlike strand that circles the move. cell in a groove along its body. This flagellum allows the cell to turn over and change direction. The combination of the two flagella cause this protist to turn in a spiral as it moves forward. Some species also have a covering of stiff plates that form a protective armor. Some dinoflagellates, such as Noctiluca, are bioluminescent; that is, they HMDScience.com can produce light through internal chemical reactions. The name Noctiluca GO ONLINE means “night-light.” If you have ever visited the ocean at night, you may have Comparing Protists seen these tiny, blue glowing organisms along the surface of the water. They give off light when they are disturbed. The light may act as an alarm to help them avoid being eaten. ©Andrew Syred/Photo Inc. Researchers,

564 Unit 6: Classification and Diversity DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A

Certain other photosynthetic dinoflagellates help build coral reefs through their symbiotic partnership with corals. These dinoflagellates live in the inner tissues of the corals. In return for shelter from the corals, the dinoflagellates provide the corals with nutrients in tropical waters that are usually nutrient-poor. Some species of dinoflagellates produce toxins. A large population of these dinoflagellates can create what is known as a red tide, due to the reddish color produced by a high density of these species. Red tides, shown in FIGURE 3.3, occur when changes in ocean currents Dinoflagellates bring up nutrients from far below the ocean surface. The higher nutrient levels produce a rapid increase, or bloom, in the dino- flagellate population. A toxic bloom in the waters can kill large numbers of fish. The toxins can also build up in the tissues of shellfish, which then can be dangerous to humans who eat the contaminated seafood. Diatoms Most diatoms (phylum Bacillariophyta) are easy to recognize when viewed through a microscope. These tiny single- celled algae are covered with delicately patterned glasslike shells. The shells of diatoms serve almost as an external skeleton, helping the FIGURE 3.3 A high density of cell to hold a rigid shape. Diatom shells, such as those shown in FIGURE 3.4, dinoflagellates causes reddish are made of silica, the same brittle substance that is used to make glass. The coloration of ocean waters, called silica shell is divided into two parts that overlap each other, like the lid of a box. a red tide. The toxins produced during a red tide can kill sea life Like other autotrophs, all diatoms release oxygen into the environment. and cause illness in humans. In fact, diatoms could be considered the world champions of photosynthesis. (colored SEM; magnification about 8503) They play a critical role in the uptake of carbon dioxide on Earth and produce about half of the oxygen we breathe. Diatoms may be freshwater or marine. R E ADI N G TO OLB ox Many species are phytoplankton. Others live clinging to rocks, plants, soil, VOCABULARY and even animals—diatoms have been found growing on crustaceans, turtles, The name diatom comes from and even whales. Because of their glassy, mineralized shells, diatoms have the Greek term diatomos, been well preserved in the fossil record. Some fossil rocks consist almost meaning “cut in half.” This refers to the appearance of the entirely of diatoms. These diatom skeletons have many industrial uses, such as diatom’s overlapping shell. an ingredient in scrubbing products, because of their rough texture.

Figure 3.4 diatoms Diatoms are known for their delicate glasslike cell walls, or shells, that can have many shapes. They are common in both freshwater and marine environments.

(all colored SEMs; magnification 750; magnification 250; magnification unknown) (tr) ©Bill Bachman/Photo Inc.; Researchers, (inset) ©Steve Gschmeissner/Photo Inc.; Researchers, (bl) ©Andrew Syred/Photo Inc.; (br) Researchers, (bc), ©Susumu Nishinaga/Photo Inc. Researchers,

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FIGURE 3.7 Life Cycle of Single-Celled Green Algae Some single-celled green algae, such as Chlamydomonas, undergo sexual as well as asexual reproduction.

Meiosis occurs within the haploid zygote, producing four cells (1n) haploid cells that will grow meiosis mitosis and mature. During asexual repro- duction, the cell divides by mitosis. zygote (2n) Sexual reproduction Asexual reproduction Gametes fuse, forming a diploid zygote.

mature The daughter cells develop cell (1n) flagella and become zoo- mitosis gametes (1n) spores, which become During sexual reproduction mature haploid cells. mitosis produces many haploid gametes.

Sexual reproduction occurs in algae as well. Some species alternate genera- tions so that the offspring from sexual reproduction reproduce asexually, and the next generation then reproduces sexually. In other species, asexual repro- duction occurs for several generations until conditions change. For the single- celled Chlamydomonas, sexual reproduction is triggered by stress such as lack of moisture or food. As shown in FIGURE 3.7, it begins with cells dividing by mitosis to produce one of two types of gametes. Because the gametes look Biology IDEO identical in most species of Chlamydomonas, they are usually identified as V CLIP different mating types, labeled + and –. When the gametes come together, they HMDScience.com

join and form a diploid zygote. The zygote may develop into a zygospore by GO ONLINE making a thick wall that can protect it during unfavorable conditions. When Review of Algae favorable conditions return, meiosis occurs, producing four haploid cells. Apply Explain how sudden population increases, or “blooms,” of algae may occur. Self-check Online HMDScience.com 19.3 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. Give an example of each of the 3. Classify If a multicellular organism Ecology following: a single-celled, a colonial, contains chlorophyll c but no silica, to 5. Draw a simple food web for a and a multicellular plantlike protist. which phylum does it likely belong? marine ecosystem. Include 8b 8C dinoflagellates, fish and 2. Many plantlike protists, or algae, 4. Analyze Many biologists argue that shellfish, diving birds, and reproduce sexually when conditions the euglenoids should be classified humans in your diagram. are harsh. Why might this be benefi- as an animal-like protist rather than a What might happen if cial? plantlike protist. Explain. 8b, 8c nutrient levels in the water increased? 12c

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19.5 Diversity of Fungi

8B, 8C, 11C, Key Concept Fungi are heterotrophs that absorb their food. 12A MAIN IDEAS VOCABULARY Fungi are adapted to absorb their food from the environment. chitin Fungi come in many shapes and sizes. hyphae Fungi reproduce sexually and asexually. mycelium fruiting body mycorrhizae Connect to Your World sporangia What is the largest living thing in the world? The blue whale? A giant redwood tree? Although they are big, both species are tiny compared with a fungus growing in Oregon—a single honey mushroom, Armillaria ostoyae. Most of it is underground, 8B categorize organisms using a hierarchical classification but this mushroom could cover more than 1500 football fields. It is thought to be at system based on similarities and least 2400 years old. As amazing as it sounds, there are other fungi throughout the differences shared among groups; 8C compare characteristics of world nearly as large. taxonomic groups, including archaea, bacteria, protists, fungi, plants, and animals; 11C summarize the role of MAIN IDEA 8B, 8c microorganisms in both maintaining and disrupting the health of both Fungi are adapted to absorb their food from organisms and ecosystems; 12A interpret relationships, including the environment. predation, parasitism, commensalism, mutualism, and Despite how little most people know about fungi, they are all around us—in competition among organisms soil, water, and even in the air. Many forms live in and on plants and animals. Scientists have named about 70,000 species but estimate there may be a total of 1.5 million fungi species in the world. Comparing Fungi and Plants Members of the kingdom Fungi fall into one of three groups—the single-celled yeasts, the molds, and the true fungi. For many years, biologists classified fungi as plants. But there are a few traits that separate these two kingdoms. • FIGURE 5.1 A mushroom is Plants contain chlorophyll and photosynthesize. Fungi do not have actually just the reproductive, chlorophyll and get food by absorbing it from their environment. or fruiting, body of a fungus. • Plants have true roots, leaves, and stems, but fungi do not. Most of the fungus grows in • Plant cell walls are made of the polysaccharide cellulose. Fungal cell walls the ground, as a mycelium. are made of chitin (KYT-uhn), a tough polysaccharide that is also found fruiting body spore-producing in the shells of insects and their close relatives. structures Anatomy of Fungi With the exception of the yeasts, fungi are multicellular organisms. The bodies of multicellular fungi are made of long strands called hyphae (HY-fee). Hyphae (singular, hypha) are shown in FIGURE 5.1. Depending on the species, each hypha may consist of a chain of cells or may contain one large, long cell hyphae with many nuclei. In both cases, cytoplasm can flow freely throughout the mycelium hyphae, and each hypha is surrounded by a plasma membrane and a cell wall of chitin.

Chapter 19: Protists and Fungi 571 CorrectionKey=B DO NOT EDIT--Changes mustbemadethrough “File info” 572

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How is the way that fungi get their food different from that of any other other any of that from different food their get fungi way that the How is u’ve ever let an orange grow moldy, you’ve chrysoge Penicillium seen i absorb from food their environment. their from can The be food a east that makes bread is Saccharomyces rise cerevisiae E A

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(t) ©Robert Marien/Corbis; (b) ©Vaughan Fleming/Photo Researchers, Inc. CorrectionKey=B DO NOT EDIT--Changes mustbemadethrough “File info”

(t) ©Kenneth H. Thomas/Photo Researchers, Inc.; (b) ©J. Forsdyke/Gene Cox/Photo Researchers, Inc. Fungi reproduce sexually and asexually. and sexually reproduce Fungi my Identify

nitrates and ammonia, whichplants the use. inorganic take they nitrogen from and soil the convert it to plants. Mycorrhizae help plants these nitrogen—that to fix is, mutualistic partnerships and fungi between roots the of certain with other haploid spores to form diploid yeast cells. may reproduce then more haploid spores through budding. Othersmay fuse undergoesascus budding, releasing each of haploid the spores. Some spores anThe haploid ascus. called nuclei it contains are of atype spore. actually The plasm dividing, it produces characteristic the saclike structure of phylum this notdoes that divide. ayeast of Recall fungi. is Instead atype sac of cyto- the meiosis, producing four haploid nuclei. However, parent the cell’s cytoplasm nucleus. When buds these reach detach and size, they acertain form acell. parent forms cell bud asmall of cytoplasm that contains also acopy of the cytoplasm divide, making two identical daughter budding, cells. During the Fission is identical to mitosis—the cell’s DNA is copied and nucleus the and simple fission or through aprocess budding, called shown inFIGURE5.4. Yeasts are fungi.reproduce single-celled They asexually, either through Fungi Single-Celled in Reproduction variety of strategies. Most reproduce fungi and through sexually asexually awide both shownPuffballs, in which are of two that types fungi inplants. cause diseases bracket, or shelf, fungi. It includes also and rusts the smuts, club-shaped. This phylum includes mushrooms, and puffballs, The club are get fungi name their bodies fruiting their because Fungi Club belongs to group. this or decaying matter. At least one group of symbiotic fungi Most members of phylum this by get food decomposing dead to ferment to used foods fungi such foods as certain soy sauce. The bread molds range from molds the you on spoiled see Molds Bread little shelf. forests, where grow they outward forming from tree trunks, a mature body. fruiting Bracket are fungi acommon sight in release spores their someone when or something strikesthe MAI corrhizae? Som N

ID What two organisms share a mutualistic partnership in the formation of of formation the in partnership amutualistic share organisms two What e yeasts undergo reproduction. sexual Adiploid yeast undergoes cell E A

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Life CycleofZygoteFungus GO ONLINE the parent. identical to each other andto The offspring are genetically involve thejoiningofgametes. single parent that doesnot creation ofoffspring from a asexual reproduction isthe Growth andDivisionthat Recall from thechapter Cell Rep A Unit 6:Clas o (Ascomycota) Sac fungi (Zygomycota) Bread molds (Basidiomycota) Club fungi Fungi F s C igure ex f ONNE r

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r TO t ep i on Biology r o duc asci Reproductive feature t iv e basidia zygospore s t ruc t ur fungi, mosses, algae, and ferns. variety of organisms, including some similar reproductive structures of a sporangium The term structures at tips the of hyphae. their spores in reproduceThey by asexually producing there when asexually is plenty of food. reproduce supply food the when sexually is low but reproduce can also cause of form structures the they reproduction. during sexual Bread molds Bread molds • • • • •

e The n The s Whe The t As inth produce more zygospores. more produce spores insporangia. may Or they reproduce sexually, by fusing hyphae to haploid spores. that can tolerate long of extreme periods conditions. different mating types. hyphae that but alike look are duction inzygote involves fungi s

n the conditionsn the become favorable, asporangium grows and produces wo types ofwo types hyphae nuclei their fuse to produce adiploid zygospore pores are released and can grow into hyphae. new ew hyphaeew inturn may reproduce asexually, by forming haploid sporangia, e club repro- fungi, sexual Examples of life cycles for two phyla of are fungi shown in The multicellular have fungi complex reproductive cycles. Fungi Multicellular in Reproduction • • • • • • reproduction.sexual fungi, other the unlike phyla, spores are most often formed by that formThey gills you within leaflike the canIn easily see. club reproduction. are Basidia found on undersides the of mushrooms. where basidia, structures spores called are produced during sexual Club fungi FIGURE 5.6.

Mem Som If th The s The zy Nuc An en as mushrooms.as formation the can trigger of aboveground such bodies fruiting mycelium underground. cells of another haploid mycelium, producing adiploid form haploid hyphae. by contact with animals. lei within the basidia fuse to formlei within fuse basidia the diploid zygotes. e spores land inafavorable environment, grow they and e cells of haploid the mycelium may with the fuse bers ofbers Zygomycota are known also as zygote be- fungi pores drop from and gills are the away carried by wind or spore-forming vironmental cue,such as rain or change intemperature, gotes undergo meiosis to form haploid spores. is used to describe to describe is used

Bas idiomycota are named for club-shaped their VISUAL VOCAB Sporangia produce spores. spores are structures that sporangia

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FIGURE 5.6 typical Life Cycles of Fungi

Reproduction in fungi can occur in several ways. Although most club fungi reproduce sexually, bread molds can reproduce both sexually and asexually.

Life cycle of club fungi meiosis basidia

zygotes Nuclei fuse within basidia to form Zygotes undergo zygotes (2n). meiosis to form n nuclei (1n) spores (1 ). Spores are Sexual reproduction dispersed by wind.

growth underground A mycelium (2n) grows Spores grow into hyphae A fruiting body, or underground. of opposite mating types mushroom, develops underground. aboveground.

life cycle of bread molds

The sporangium bursts and releases spores (1n).

Sexual reproduction Asexual reproduction A zygote Some hyphae grow produces a above ground and sporangium (1n). produce sporangia (1n). meiosis mitosis Gametes (1n) of A spore different mating produces The gametes fuse and a types form at the hyphae (1n). zygospore (2n) forms. It tip of hyphae. has a thick wall and can remain dormant for a long time. A mycelium (1n) grows.

CRITICAL How are the life cycles of club fungi and bread molds similar? VIEWING How are they different? 8c (tl) ©Orla/ShutterStock; (c) ©Mauritius, GMBH/Phototake (tl) ©Orla/ShutterStock; (c) ©Mauritius,

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(magnification 400× encased inanascus. of asa the cup-shapedfruitingbody FIGURE 5.7 19.5 Unit 6:Clas 2. 3. 1. Re

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M fruiting bodyof ascospore ai ascus n I hyphae to d e as Hypothesize are conidia, which means called “dust,” travel they because easily through air. reproduction.during sexual Spores produced during reproduction asexual produce different of types spores during reproduction asexual do than they tions are favorable and reproduce conditions when sexually are harsh. They are asource also of for allergies many people worldwide. leftover cannot food avoided, be is refrigerated. food even ifthe Fungal spores spores air inthe at any given is time reason the that growth the of mold on our than 150kilometers (93mi) above The great of surface the Earth. number of from greater this height. stops climbing and remains inplace. fixed The fungus releases then its spores to climb insect the into high atree or other vegetation. Eventually, insect the grow onIn insects. penetrate some fungi the species, insect’s the brain, causing in releasing spores. their For example, members of genus fungal the Cordyceps location.new of and Some species gounusual fungi use even further strategies source. This strategyallows spores small the inair currents carried to be to a Fungi release spores their at tips the of hyphae, their above high food their Release Spores of Lik Spo e the breade the molds, usually reproduce fungi sac condi- when asexually res of and are fungi have everywhere, found even been air inthe more 5. 4. C cup-shaped collapses, body and fruiting releases spores. the body. Inside haploid ascus, the spores form. When mature, the orAn develops ascus, sac, at tip the of each hypha within fruiting the The joinedtypes. hyphae grow into aboveground the body. fruiting involves fungi sac joining the of two mycelia that are different mating in club and fungi bread molds,reproduction sexual inmulticellular Most are asci found within fungi’s the cup-shaped body. fruiting As reproduction. reproductive These structures are shown inFIGURE5.7. th Sac fungi

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The Other KINGDOM

Web BIOLOGY Sickening Protists Learn Comparing Protists Protist and Fungus Life how to diagnose and treat Run an experiment on different Cycles Build the life cycles three patients with diseases samples of protists to determine of a slime mold, a cup caused by protists. which of them are autotrophs and fungus, and brown algae. which are heterotrophs. (l) ©Eye of Science/Photo Inc. Researchers,

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pathogens or mutualists to other organisms—including humans. as decomposers act Some fungi environment. inthe as either Othersact check for and remove molds that are established homes. intheir its and walls, spores their can cause respiratory illness. Homeowners should houseswooden and boats. Molds and other inside fungi a house can weaken ever. Fungi can damage trees, cause and fruit can also damage they inside MAI MAI C Fungi Fungi o The d N n N ID ce IDEAS

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(c) ©Roger Tidman/Corbis; (b) ©Stephen Dalton/Minden Pictures fungus that is transmitted by shown elm bark beetles, in devastating inagriculture and horticulture. Dutch is caused by elm disease a Fungi and plants cine that harm cells fungal but will not damage human cells. cellulartheir similar to structure ours. is very It to develop is difficult medi- death. Fungal infections are hard to treat are fungi because eukaryotes, and so such asdiseases, some lung that illnesses, are hard to cure and can even cause But cause fungi effects. mild severe several cause and ringworm athlete’s foot, have fairly tions may grow and cause disease. human’s immune system is damaged, popula- body,the such as skinand the mouth. If a yeast Candida that of occupy parts certain healthy humans have populations of the functioning at its For best. instance, all immune the when disease system is not thrive. Typically cause harmless also fungi allowing other organisms such asto fungi human inthe bacteria digestive system, Antibiotics can destroy beneficial certain ample of how humans allow pathogens an opportunity to cause infection. Fungi andhumans infection. in the host’s body provides them an opportunity to grow unchecked and cause change host’s inthe homeostasis are opportunistic called pathogens. Achange Organisms tolead disease. that normally don’t cause aproblem until there is a However, changes inenvironmental circumstances can upset and balance this harmless, coexisting with other organisms inadelicate balance. ecological gens—the term obligate or means obliged. necessary are fungi Other normally pathogenic always fungi are causefungi These obligate disease. called patho- some pathogenic, can fungi be bacteria, Like or disease-causing. Afew Fungi as treatments if they are overused. These products should be used carefully. other fungi. Like bacteria and protists, however, fungi can develop resistance to usually come from fungi themselves, which produce them as a defense against humans, are usually treated with antifungal medications. These treatments are becoming more common. Fungal diseases in animals, including those in fungicides. Today, however, crops that are genetically engineered to resist fungi and is amajor cause of spoilage fruit during shipment and storage. produce such This fungus as strawberries. can grow even inrefrigerated fruit in millions of dollars inlosses to growers each year. Gray of mold is adisease is scab causedcrops. by peach of afungus called peaches and Adisease results Unitednorthern States. Fungi destroy also alarge portion of world’s the fruit 1930. Today, has destroyed disease the more than of half elms the in the United States, of first cases the Dutch were elm disease reported inOhio in Som Fun gal diseases in agriculture are often treated with chemical sprays called e fungal pathogens,e fungal such that as those P athogens

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T O mycelium provides habitat for thealgae. Algae cells feed thefungusthrough photosynthesis, andthefungal A lichenisasymbiotic relationship between analga andafungus. 6.3 FIGURE as tundra, where could fungi not alone. survive temperatures. This characteristic of lichens allows to them live inhabitats such are common environments. incool, dry withstand can They also severe can grow on almost any solidsurface, to from to soil rocks. tree trunks They sugars that and alga the both feed fungus. the Lichens (phylum Mycomycota) produce chemicals with antibiotic properties that help bacteria. fight harmful forneed which can fertilizers, cause and soil water pollution. Mycorrhizae also nutrients from plant. the Mycorrhizae plant can boost growth and reduce the could alone. In return, fungus the it because benefits gets sugars and other mycelium can absorb nutrients soil and water faster than plant’s the roots mycelium is much larger than root the area surface of plants, the the so colonize roots the of anearby plant. The huge area surface of fungal the mycorrhizae on roots. their Mycorrhizae form hyphae the when of a fungus are mycorrhizae. called More than 80percent of world’s the plants have Mycorrhizae antibiotic properties. pigments as dyes used intraditional cultures and compounds that have and aproducer. Lichens produce hundreds of unique chemicals, including important innutrient adecomposer as function both cycling,they because to air pollution andas indicators used can be of air quality. Lichens are also sion, can live they because on bare rock. Many of species lichens are sensitive of humans. For example, are they extremely important during succes- primary FIGURE 6.3. FIGURE Lichens form mutualistic relationships of types organisms. with several Mutualism is asymbiotic relationship organisms inwhich both Fungi benefit. Fungi Mutualists as fungal hyphaefungal that surround and grow into cells, as shown algal the in can combineria to form alichen body. itself The consists body mainly of and or algae photosynthetic fungi, algae, Only certain or bacteria. cyanobacte- Densely packed Densely packed Loosely packed Lic fungal hyphae fungal hyphae fungal hyphae Layer ofalgae hens play roles several environment inthe and lives inthe

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turn on feed mycelium. fungal the leafthe pieces and absorbs nutrients from The them. ants in Next, ants the add pieces of fungus. the The fungus breaks down underground nest area, where build agarden they of leaf pieces. plants leaf pieces these back to withan jaws. their carry They grow actually they ants These them. cut tiny pieces of leaf from and are easy to culture, or raise, in the laboratory. can often applied be to multicellular organisms. Yeast are small, grow quickly, found inplants and animals. Insights gained from studies of a yeast’s genome molecular biology. Most yeasts have many of same the genes and proteins organismssingle-celled are among most the important modelsystems in used against bacteria. human digestive time, have fungi Over tract. evolved natural defenses space and nutrients. live they whether on This is aforest true or floor ina natural habitats and compete fungi bacteria for similar resources, such as knowledge is applied then to develop medicines. For useful example, intheir researching how pathogens interact with natural their environments. This industry. of Since discovery the antibiotics 1900s,scientists inthe have been and drinks insoft some candy.used Fungi care health inthe are useful also yeastthe we to use bread. bake In addition, make fungi citric acid, which is Many of species are fungi edible, such as mushrooms the we eat on pizza and and South America,shown in a mutualistic symbiosis with fungi. The leafcutter ants of Central Fungal gardens and insects

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CHAPTER 19 G N I D A E R

matches each numbered item below. In your notebook, write thevocabulary term that L

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hyphae, my fruiting body, sporangi prot mycorrhiza slime mold, wa rhizae. “root.” Explain how these meanings relate to mycor mukes, whichmeans “fungus,” and rhiza, whichmeans The term my which means “w The term hyphae comes from theGreek word huphe, pseudopod, cili to hyphae.

cilia ps protozoa algae protist ozoa, algae eudopod D Review ia X O B L O O T grams e, lichen c V celium abu corrhizae comes from theGreek words ocabulary ter mold a eb.” Explain how thismeaning relates lary 10. a Word Word and Greek 11. O ri g L ins 19.5 19.4 ati n

wa slime mold my hyphae chitin ter mold celium ­-

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Why are ye briefly describe thediseases they cause. Name two animal-lik asexual andsexual reproduction? How can thehy placing organisms inoneortheother ofthese phyla? the kingdom Fungi. What structures are thebasisfor The phyla Asc funguslike protists? one reason they are classified withwater molds as Slime molds hav When doesanamoebaform aps be thebasisfor thisreclassification. regr Explain whythephyla ofthekingdom Protista mightbe expl Give onecharacteristic ofeach typeofprotist that cia How isthedecomposing activity offungiboth benefi- fungi. Describe sexual reproduction inyeast, orsingle-celled Explain how hyphae helpafungusabsorb food. How domulticellular algae reproduce asexually? answer. or multicel Are protists classified onthebasisofbeingsingle-celled pro What are three typesofstructures that helpsome l andharmful? tists move? ouped into several kingdoms andwhat would likely ains whyitisanimal-like, plantlike, orfunguslike. HMDScience.com Interact 8b, 8c 8b, 8c 11c, 12a

lular? Give anexample to your support 19.6 asts useful to scientific research? M omycota andBasidiomycota are both in 8b, 8c AIN phae ofbread molds beinvolved inboth

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e protists that cause disease and IDEAS 11c 8b, 8c Chapter 19: Protists andFungi Chapter 19: eudopod? 8b, 8c 11c

583 CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info”

584 brown algae

Use the diagram below to answer the next two questions. I Critical 28. 26. 30. 29. 32. 27. 31. nterpreting Unit 6:Clas

P become less healthy. instead. Explain whythefarmer’s crops may actually of fungiischeaper, and thefarmer decidesto use it Butabroad-spectrumit. fungicidethat manykinds kills a fungicidethat targets only thiskindoffungusandkills with fungiandplants? relationship between fungiandanimals, ascompared Classify A A algae orplants? Explain your answer. I A one form ofacellular slimemold? Why istheterm pseudoplasmodium used to describe D What phylumwould itlikely beplaced in? marine environment, bodycovering made ofcellulose. has thefollowing characteristics: two flagella, found ina protists onland orwater? Explain your answer. Would you expectto findeach ofthese typesof have flagella, andciliates have cilia to helpthemmove. from beingclassified asanimals, plants, orfungi? nterpret redic nalyze nalyze nalyze red algae escribe t 8b, 8c 8b, 8c sification andDiversity green algae

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8b, 8c plasmodial slime molds

cellular slime molds kingdom Fungi 8b, 8c 8b, 8c kingdom Animalia the next four days and recorded their observations. Both students looked at the banana pieces every day for

Two 3-cm posing fruit would speed up the rate of decomposition. two students to determine if adding yeast to a decom- questions. The following experiment was conducted by Use the text and the data below to answer the next two A Making Connections student took one of the banana pieces home. in a different plastic bag and the bags were sealed. Each

36. 34. 35. 33. O P Student B’s banana Student A’s banana • • nalyzing er

rg bookshelf. resealed Healso thebag. puthisbananapiece ona Student Bputsome dryye your answer. feeding strategy? ageneralist feeding strategy? Explain one advantage anddisadvantage ofhaving aspecialist the Paramecium onthechapter opener. What mightbe E explains whythey can beneither plants noranimals. with plants. Includethedecisionofreferee who placed withanimals andtheother wants to be placed between two euglenoids inwhichonewants to be Write an Student Aplac Explain. the questionthat thestudentswere tryingto answer? A this experiment? E valuate xperimenta nal c anism ent yze 2 pieces of banana were cut. Each was placed 8b, 8c D

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Record your answers on a separate piece of paper. 8C, 12A MULTIPLE CHOICE 4 Most fungi are decomposers. How do their life processes affect other organisms in the community? 2C, 6H, 8C A Fungi keep other populations under control by 1 When scientists first observed protists with preying on weak organisms. chlorophyll, they thought the protists were B Fungi make stored nutrients available to other actually single-celled plants. By using more organisms. recent molecular techniques, scientists have C Fungi compete with plants for soil nutrients. determined that these organisms are genetically D Fungi compete with plants and animals for different from plants. This is an example of — space. A how scientific theories can change with the development of new technologies THINK THROUGH THE QUESTION B why scientific theories should not be If you are having a hard time answering this question influenced by new scientific evidence in terms of fungi, try to consider it based on the role of decomposers in general. C why all scientific investigations should involve genetic analysis D why protists should be classified as plants 2G

4A, 8C 5 nucleus 2 chloroplast

eukaryote: prokaryote: protists, fungi, bacteria, plants, archaea animals

A researcher discovers a new type of organism. The grouping of kingdoms into prokaryotes and Only some structures, labeled above, can be seen eukaryotes is shown in the Venn diagram above. clearly. Based on this information, the researcher One cellular characteristic that could be placed in is able to conclude that the organism — the area that overlaps both groups is — A is a protist that lives in colonies A nucleus B is a multicellular protist B organelles C can capture energy from the sun C chloroplasts D will not prey upon other organisms D cell membrane

8c 12E 6 Yeast is a single-celled fungus that can reproduce 3 Diatoms carry out a large portion of the both asexually and sexually. How is sexual photosynthesis that occurs on Earth. In which reproduction in a yeast cell different from sexual biogeochemical cycle do diatoms probably have reproduction in animals? the greatest effect? A In a yeast cell, the DNA is not copied. A phosphorus cycle B The yeast cell does not undergo meiosis. B nitrogen cycle C During meiosis, a yeast cell produces only two C carbon cycle haploid nuclei. D water cycle D During meiosis in a yeast cell, the cytoplasm does not divide.

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Careers Pandemics— Bio Bytes Is the Next One

Opinion Poll on the Way? Imagine that a new virus emerges and Strange Biology people have no immunity. There is no vac- cine. If this were to happen, there could be mandatory travel restrictions, quarantines, and social distancing—including staying out of all crowded places. In the United States alone, such an outbreak could kill up to 2 million people. But how can such a virus emerge, and how can we prepare for it? (tr) ©age fotostock/SuperStock; (cr) ©Alfred Inc. Pasieka/Photo Researchers,

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If a new and deadly disease emerges today, a pandemic could rapidly result. A carrier could travel around the world in 24 hours. Several million people travel internationally by plane every year, easily reaching their destinations before they show any symptoms of carrying a disease.

The “Perfect” Virus 4C Pandemics Not every virus is well suited to cause massive human When a new virus emerges, it infects organisms that casualties. For many viruses, humans represent a have not developed immunity, or resistance, to the dead-end infection because they cannot be passed virus. If a new virus infects humans, it may spread from human to human. For other viruses, victims die easily from person to person before a vaccine can be too quickly for the virus to reproduce. Quarantines produced. A disease outbreak that affects large areas can contain this type of virus relatively easily. of the world and has a high fatality rate is called a What characteristics would make an emerging pandemic. The disease is spread very quickly through virus likely to cause a pandemic? The virus would infection—for example, by sneezing or coughing—to need to be adapted to humans as hosts and easily a great number of people. spread through casual contact. Victims would also The 1918 flu pandemic was the most devastating have to survive infection long enough without pandemic recorded in world history. This virus symptoms to go about their daily business and infect infected nearly one-fifth of the world’s population, other people. Finally, the most deadly virus would killing about 50 million people worldwide. It spread mutate rapidly, foiling the attempts of scientists to mainly along global trade routes and with the move- develop a vaccine or a drug that targets it. ment of soldiers during World War I. TECHNOLOGY

Dissecting a Virus 4C Scientists have long debated how the genetic material of influenza A viruses, RNA, is likely arranged. In 2005 virologist Yoshihiro Kawaoka and his team of researchers at the University of Wisconsin unraveled the mystery using a technique called electron tomography. Electron tomography is a way to construct a three-dimensional image from a series of electron microscope images taken at different angles. By making slices along flu virus particles that cut them into “top” and “bottom” halves, research- ers found that all influenza A viruses have a total of eight RNA strands. As shown at the right, seven strands form a circle just inside the edge of the virus particle, surrounding an eighth strand in the center. Based on this similarity in structure, the researchers concluded that all influ- enza A viruses must share a specific mechanism for packaging their genetic material. This knowledge may make it possible to engineer viruses that can be Read More >> at HMDScience.com used to mass produce vaccines to defend against these viruses, which are

(tl) ©The Art Archive/Culver (tl) Art Pictures/Picture ©The Desk; Kawaoka (tr) Noda ©Ian Yoshihiro and Miles-Flashpoint Takeshi Pictures/Alamy; (br) ©Drs. responsible for regular seasonal outbreaks as well as the avian flu.

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UNIT 6 BioZine

CAREERS

Epidemiologist in Action dr. Ben Muneta TITLE Medical Epidemiologist, Indian Health Service

EDUCATION M.D., Stanford University

In 1993, a mystery disease began to kill people in the southwestern United States. One of the experts that the Centers for Disease Control (CDC) consulted was China, Thailand, Russia, Turkey, and Pakistan are among Dr. Ben Muneta. Dr. Muneta is an epidemiologist, a the countries that have confirmed cases of avian flu in scientist who studies the causes, transmission, and poultry farms. Here, a Pakistani health worker vaccinates a healthy chicken. control of diseases within a population. He works at the Indian Health Service National Epidemiology Program in Albuquerque, New Mexico. Avian Flu H5N1 4C Dr. Muneta consulted a traditional Navajo healer. Perhaps the most familiar zoonosis is the avian flu From him, Dr. Muneta learned that the disease was virus. Sometimes called the bird flu, this virus nor- associated with extra rainfall, which had caused the mally infects wild birds such as ducks and geese as well pinon trees to produce more nuts than usual. This in as domestic birds such as chickens. Migrating birds turn had led to a population explosion among mice can carry it to other continents. that feed on these nuts. Researchers have been tracking a form of avian flu Using this lead, CDC researchers determined that called H5N1. Like other flu viruses, H5N1 mutates the disease was caused by hantavirus, a virus spread rapidly. Random mutations may or may not help the through the droppings of deer mice. With further research, Dr. Muneta confirmed that some Navajo virus adapt to new host species. However, viruses can healers had even predicted the 1993 outbreak. mutate in a faster, less random way. If an animal becomes infected with viruses from two different Read More >> at HMDScience.com species at the same time, the viruses can exchange genetic information. If this happens, the avian flu can Diseases That Jump to New Species jump the species barrier, becoming a flu virus that 4C can be transmitted from one human to another. A zoonosis is a disease that can jump between 3A, 3D species. A virus that evolves the ability to jump from Unanswered Questions a nonhuman animal species to humans will spread Despite the danger that a new virus represents, no very quickly in the human body, which has not yet one knows how the virus may mutate or whether it developed defenses. If this virus exchanges genetic will cause a pandemic. Some of the most important material with another human virus, the virus may questions include the following: become capable of spreading from person to person. • How can vaccines be developed quickly enough to The swine flu pandemic was caused by the H1N1 stop a disease that can spread in hours or days? virus that originated in pigs. In 2009, it was estimated • Can a broad-spectrum antiviral drug be developed that 22 million people were infected with the H1N1 that could target more than one flu virus? virus! World health officials urged individuals to get • What specific molecular factors allow a virus to vaccinated and educated people on its symptoms. A jump from one species to another? year later, the swine flu was officially contained.

Read More >> at HMDScience.com Ben (tl) Muneta ©Photo courtesy of of Dr. Jana Muneta; (tr) ©Ali Imam/Reuters/Corbis

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