Reading Essentials for Biology Glencoe (794133), страница 52
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A plasmodium isa mass of cytoplasm that contains manydiploid nuclei but no cell walls or membranes. When a plasmodial slime moldlooks like a slimy mass, it is in the feeding stage. The plasmodium eats by moving along decaying logs or leaves andsurrounding its food.
Faster plasmodiGums travel at 2.5 centimeters per hour.At that rate, a plasmodium would crossthis page in about eight hours.A plasmodium can be more than a meter in diameter. If foodand moisture become scarce, a plasmodium will change by transforming itself into many separate stalks. Each stalk is a sporeproducing structure. That means that meiosis takes place in thestalk and produces haploid spores. When the wind blows, thespores are carried away.
The illustration above shows the lifecycle of plasmodial slime.Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.How do cellular slime molds differ?Cellular slime molds have a different life cycle than plasmodialslime molds, so they have been placed in a different phyla. Cellularslime molds spend part of their life cycle as single amoeba-likecells. They feed, grow, and divide by cell division.When food becomes scarce, these independent cells join withhundreds or thousands of others to reproduce. When they gettogether, they look like a plasmodium.
However, this mass of cellsis multicellular. That means it is made up of many individual cells,each with a distinct cell membrane. This multicellular mass formsa single stalk that produces spores. You can see the process illustrated on page 220.CReproductivestagesDEFGrowthstages2. How do cellular slimemolds differ from plasmodial slime molds?________________________________________________________________________Water Molds and Downy MildewsThe third phylum of the funguslike protists contains the watermolds and downy mildews.
These organisms live in water or moistplaces. Some feed on dead organisms and others are plant parasites.READING ESSENTIALSChapter 19219NameDateClassSectionSlime Molds, Water Molds, and Downy Mildews, continuedCellsgatherSporesAmoeba-likecells releasedCells feed,grow, and divideMulticellularamoeboidlikemass formsSpore-filledcapsule on astalk formsThe sluglikestructuremigratesThe mass compactsand forms asluglike structure3. Analyze How are watermolds and downymildews different fromslime molds?________________________________________________4. What evidence suggeststhat ancient green algaewas the ancestor of modern plants?Most water molds looklike fuzzy, white growth ondecaying matter.
Theyresemble some fungi. However, at some point in theirlife cycle, water molds produce reproductive cellswith flagellates—somethingthat fungi never do.Downy mildew led to aserious famine that struckIreland in the mid 1800s.At the time, the major foodcrop for the people ofIreland was the potato. Adowny mildew destroyedmost of the potatoes. During the famine that followed, many Irish citizensmoved to other countries,including America.Origin of ProtistsNow that you have studied the various protists, you may bewondering how protists are related to the animals, plants, andfungi they resemble.Currently there is not conclusive evidence that suggests thatancient protists were the evolutionary ancestors of fungi, plants,or animals, nor is there enough evidence to say that protistsemerged as a separate evolutionary line.
However, after analyzingRNA, many biologists agree that ancient green algae were probably the ancestors to modern plants.________________________________________________220Chapter 19READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.19.3NameDateClassSection19.3Slime Molds, Water Molds, and Downy Mildews, continued◗ After You ReadMini Glossaryplasmodium: in plasmodial slime molds, the mass of cytoplasm that contains many diploid nuclei but nocell walls or membranes1. Review the term and its definition in the Mini Glossary above. Write a sentence using theterm plasmodium on the lines below.________________________________________________________________________________________________________________________________________________________________________2.
Using the idea map below and information from this section, answer the following questions.Funguslike ProtistsBreak down organic materialsto obtain energy.Three Phylaof Funguslike ProtistsCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Plasmodial Slime Molds• Live in moist, cool places• Move and engulf food likeamoebas• Form a mass that has manynuclei but no cell walls ormembranesCellular Slime Molds• Live in moist, cool places• Move and engulf food likeamoebas• Form a mass of amoeboidcells before reproducingWater Molds and Downy Mildews• Live in water or moist,cool places• Grow and feed like fungi• Some are plant parasites.a.
How are plasmodial slime molds and cellular slime molds different?________________________________________________________________________________________________________________________________________________________________________b. How are some funguslike protists harmful to plants?________________________________________________________________________________________________________________________________________________________________________Visit the Glencoe Science Web site at science.glencoe.com to find your biologybook and learn more about slime molds, water molds, and downy mildews.READING ESSENTIALSChapter 19221NameDateClassSection20.1 What is a fungus?◗ Before You ReadSC.F.1.4.2 The student knows that body structures are uniquely designed and adaptedfor their function.
SC.F.2.4.1 The student understands the mechanisms of asexual andsexual reproduction and knows the different genetic advantages and disadvantages ofasexual and sexual reproduction.You have studied three of the six kingdoms so far, archaebacteria, eubacteria, and protists. In thenext two sections, you will learn about the kingdom Fungi. Fungus is the singular of fungi. Mushrooms are types of fungi. Think about places you have seen mushrooms growing. What do thoseplaces have in common? Were they hot, dry, cool, or damp? Did the mushrooms appear suddenly orgrow slowly over time? Write your thoughts on the lines below.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnIdentify MainIdeas As you read the section, draw a line from theword or phrase in the text tothe figure that illustrates it.SporeGerminatingsporeHyphaFood sourceA germinating fungal spore produces hyphaethat branch to form mycelium.222Chapter 20Fungi are everywhere.
They are in your backyard, in air andwater, on damp walls, on food, and sometimes even on your body.Some fungi are large, bright, and colorful. Most grow best inmoist, warm environments. However, you may have opened yourrefrigerator and seen leftovers covered with mold. These moldsgrow at lower temperatures.Fungi used to be classified in the plant kingdom because, likeplants, many fungi grow in soil and have cell walls. However, themore biologists studied fungi, the more they realized that fungibelong in their own kingdom. Although many fungi have cellwalls, the cell walls in fungi are made of chitin (KI tun), a complex carbohydrate. Plants have cell walls made of cellulose.MyceliumWhat is the structure of fungi?There are a few unicellular fungisuch as yeasts.
Most fungi, however,are multicellular. The basic structuralunits of multicellular fungi are long,threadlike filaments called hyphae(HI fee) (singular, hypha). The hyphaegrow from the spore of a fungus. Asthey grow, they branch to form a network of filaments called a mycelium(mi SEE lee um).
The illustrationto the left shows the spore, hyphae,and mycelium.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.The Characteristics of FungiNameDateClassSection20.1What is a fungus?, continuedWhat is it like inside the hyphae?There are different types of hyphae in themycelium. The differences are based on function. Some hyphae anchor the fungus, someenter into the food source, and others areformed only for the purpose of reproduction.Hyphae are made of cytoplasm containingmany nuclei. If you looked at a hypha undera microscope, you would see hundreds ofnuclei streaming along in a continuous flowof cytoplasm.
The flow of cytoplasm sendsnutrients throughout the fungus. Somehyphae have walls called septa that dividethe hypha into cells with one or morenuclei. The septa are usually porous, whichmeans cytoplasm, organelles, and nutrientscan pass through them.A Septa divide thehyphae of manytypes of fungiinto cells.SeptumNucleiCytoplasm NucleiCell wallCytoplasmB Hyphae withoutsepta look likebranching,multinucleatecells.Cell wallCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Adaptations in FungiSome fungi cause food to spoil, others cause diseases, and someare even poisonous. However, fungi are important and beneficial.Without fungi, the world would be overrun with huge amounts ofwaste, dead organisms, and dead plants.
Thanks to many fungi,some bacteria, and protists, the organic material is broken down andrecycled into the raw materials that other living organisms need.How do fungi get food?Fungi cannot make their ownfood. They are heterotrophs.Fungi use a process called extracellular digestion to obtain nutrients. This means food is digestedoutside a fungus’s cells and thenthe digested food is absorbed.For example, some hyphae of afungus will grow into an orange.They release digestive enzymesinto the orange that break downthe large organic molecules intosmaller molecules. These smallmolecules are absorbed into thehyphae and move into the flowing cytoplasm.READING ESSENTIALS1. The structural units of a fungusare hyphae.
The cell walls ofhyphae are made of chitin.Large foodmoleculeSmall foodmoleculeEnzyme2. The hyphae releaseenzymes into a foodsource.3. The enzymes breakdown large foodmolecules into smallfood molecules.4. The small foodmolecules move intothe hyphae.Chapter 20223NameDateClassSection20.1What is a fungus?, continued1. Identify the fungal groupthat has a symbioticrelationship.________________________________________________________________________Fungi have different types of food sources.
In fact, scientistshave given special names to fungi depending on their food source.Fungi that feed on waste and dead organic material are calledsaprophytes. Fungi that have a symbiotic (cooperative) relationship with another organism, such as algae, are mutualists. Thetwo work together to get food. There also are parasitic fungi.Parasites absorb nutrients from the cells of their hosts, often killingthe host. Parasitic fungi have special hyphae called haustoria(huh STOR ee uh) that grow directly into the host’s cells wherethey absorb nutrients and minerals from the host.________________________Every time you dig in the garden, you are helping fungi in thesoil reproduce by fragmentation.
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