Reading Essentials for Biology Glencoe (794133), страница 53
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In fragmentation, pieces ofhyphae break off a mycelium and grow into new mycelia. Everytime you dig in the soil, your shovel slices through mycelia,breaking, or fragmenting them.Fragmentation is one form of asexual reproduction in fungi.Another form is budding. Unicellular fungi called yeasts oftenreproduce by budding. During budding mitosis occurs and a newindividual pinches off from the parent.________________________How do fungi reproduce by spores?2. In what type of fungidoes budding occur?________________________3. What is a sporangium?________________________________________________________________________Most fungi produce spores.
A spore is a reproductive cell thatcan develop into a new organism. When a fungal spore arrives ina place with favorable growing conditions, a hypha comes out andbegins to grow into a new mycelium.After a while, specialized hyphae grow away from the rest of themycelium. These are used for reproduction. At the tip of a specialized hypha is a spore-producing sac or case called a sporangium(spuh RAN jee uhm) (plural, sporangia).
The sporangia are usuallythe only parts of a fungus you can see. However, the sporangiamake up only a small part of a fungus.Many fungi can produce two types of spores, one type by mitosis and the other by meiosis. This will happen at different timesduring their life cycles. The patterns of reproduction are one wayscientists classify fungi.Are spores an adaptive advantage?Consider the ways spores and their production give fungi anadaptive advantage. First of all, the sporangia protect the spores224Chapter 20READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Reproduction in FungiNameDateClassSection20.1What is a fungus?, continuedand keep them from drying out until they are ready to be released.Second, most fungi produce a large number of spores at one time.For example, a puffball produces about 1 trillion spores.
Producingso many spores increases the survival chances for the species.Finally, spores are small, lightweight, and can be easily carried bywind, water, and animals. Spores carried on the wind can travelhundreds of kilometers.◗ After You ReadMini Glossarybudding: type of asexual reproduction in whicha cell or group of cells pinch off from theparent to form a new individualchitin: complex carbohydrate that makes up thecell walls of fungihaustoria: in parasitic fungi, hyphae that growinto host cells and absorb nutrients andminerals from the hosthyphae: threadlike filaments that are the basicstructural units of multicellular fungimycelium: in fungi, a complex network ofbranching hyphaesporangium: in fungi, a sac or case of hyphae inwhich spores are producedCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.1.
Read the terms and the definitions in the Mini Glossary above. Circle one key term, then inthe space provided, write the definition of the term in your own words.____________________________________________________________________________________2. Write facts you have learned about fungi to complete the web diagram below.FungiStructuresSources of FoodMethods ofReproductionVisit the Glencoe Science Web site at science.glencoe.comto find your biology book and learn more about fungi.READING ESSENTIALSChapter 20225NameDateClassSection20.2 The Diversity of Fungi◗ Before You ReadSC.F.2.4.1 The student understands the mechanisms of asexual and sexual reproductionand knows the different genetic advantages and disadvantages of asexual and sexualreproduction.
SC.G.1.4.1 The student knows of the great diversity and interdependenceof living things. Also covers SC.D.1.4.4, SC.F.1.4.2Fungi face some interesting survival challenges. Like plants, they grow in one place and depend onthe dispersal of their reproductive cells to grow in new locations. Plants are usually taller than fungiand some depend on the wind to carry seeds long distances. Fungi are usually so low to the groundthat the air around them is still.
As a result, they have evolved some unusual features to get theirspores into the air. Some fungi, such as puffballs, shoot spores into the air. Truffles are undergroundfungi. They have a scent that animals love, so the animals dig into the ground to find the truffles,spreading the spores. A fungus called stinkhorn smells like rotting meat. It attracts flies that thenfly away covered with spores. As you read this section, think of the methods by which fungi spreadtheir spores.◗ Read to LearnIdentify Main Ideas As youread this section, stop afterevery few paragraphs and putwhat you have just read intoyour own words.Highlight themain idea in each paragraph.You may recall from the previous section that scientists classifyfungi according to how they reproduce.
Some fungi reproduceboth asexually and sexually during their life cycles. This sectioncovers several divisions in fungi.The first group of fungi you will learn about are the membersof the phylum Zygomycota (zy goh mi KOH tuh). There areabout 1000 species of zygomycotes. The mold that you findgrowing on bread is a zygomycote. Most zygomycotes decomposeorganic material. They reproduce asexually by producing onetype of spore and reproduce sexually by producing another typeof spore. The hyphae of zygomycotes do not have septa thatdivide them into individual cells.How do zygomycotes grow?1.
What is the function ofrhizoids?________________________________________________________________________226Chapter 20Let’s take a closer look at the fungus that grows on bread. It iscalled Rhizopus stolonifer. When a Rhizopus spore settles on a pieceof moist bread, it germinates and hyphae begin to grow. Somehyphae called stolons (STOH lunz) grow horizontally along thesurface of the bread. They rapidly produce a mycelium. Otherhyphae form rhizoids (RI zoydz), which penetrate the food andanchor the mycelium to the bread. Rhizoids secrete enzymes forextracellular digestion. Extracellular digestion occurs whenenzymes break down large molecules of the food into small molecules that are absorbed by the hyphae.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.ZygomycotesNameDateClassSection20.2The Diversity of Fungi, continuedHow do zygomycotes reproduce asexually?Asexual reproduction begins as hyphae grow upward anddevelop sporangia at the tips.
Spores develop in the sporangia andthen are released. The spores that land on a moist food supplygerminate, form hyphae, and reproduce asexually again.How do zygomycotes reproduce sexually?What if the bread on which Rhizopus was growing began to dryout? That unfavorable condition might cause the fungus to reproduce sexually. When zygomycotes reproduce sexually, they producezygospores.
Zygospores (ZI go sporz) are spores with thick wallsthat can withstand unfavorable conditions.Sexual reproduction in Rhizopus happens when haploidhypha from two compatible mycelia, called plus and minus,fuse. Each of them forms a gametangium.
A gametangium(ga muh TAN ghee uhm) is a structure containing a haploidnucleus. When the haploid nuclei of the two gametangia fuse, adiploid zygote forms. The zygote has a thick wall and becomesa dormant zygospore. The illustration below shows the differencebetween asexual and sexual reproduction.2. Infer What adaptiveadvantages are evident ina zygospore?________________________________________________________________________Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.SporangiaSporangiumSpores (n)Spores (n)Hypha+ Mating– Matingstrain (n)strain (n)GametangiaStolonZygosporeMeiosisGerminationRhizoidsAsexual ReproductionSexual ReproductionHow long can a zygospore remain dormant?A zygospore may remain dormant for many months.
It can survive without water and through periods of cold and heat. Whenconditions become favorable again, the zygospore absorbs water,READING ESSENTIALSChapter 20227NameDateClassSection20.2The Diversity of Fungi, continuedundergoes meiosis, and produces a hypha with a sporangium. Eachhaploid spore in the sporangium can grow into a new mycelium.AscomycotesThe Ascomycota is the largest phylum of fungi. They are sometimes called sac fungi. They have tiny saclike structures, each calledan ascus, in which the sexual spores of the fungi develop. Thesexual spores are called ascospores because they are formed insidean ascus.A different kind of spore is produced during asexual reproduction. Hyphae grow up from the mycelium, becoming longer toform conidiophores (kuh NIH dee uh forz). Then chains orclusters of asexual spores called conidia develop from the tips ofthe conidiophores.
Wind, water, and animals spread the spores.________________________________________________________________________You encounter sac fungi nearly every day. Yeasts, a type of sacfungi, are anaerobes and ferment sugars to produce carbon dioxide and ethyl alcohol. They are used in bread making becausethey produce carbon dioxide, a gas that causes bread to rise andgives it a light, airy texture. Yeasts also are used to make productswith alcohol, such as wine and beer.Yeasts are used in genetic research because they have large chromosomes.
A vaccine for hepatitis B is produced by splicing humangenes with yeast cells. Because yeasts multiply rapidly, they are animportant source of the vaccine.Truffles and morels are two edible ascomycotes. Both are prizedfor their flavor.BasidiomycotesThe phylum Basidiomycota contains mushrooms, puffballs,stinkhorns, bird’s nest fungi, rust, smut, and bracket fungi.Basidiomycotes have club-shaped hyphae called basidia(buh SIHD ee uh) that produce spores and give them their common name—club fungi.
Basidia usually develop on short-livedreproductive structures that can easily be seen. The spores arecalled basidiospores.A basidiomycote, like the mushroom in the illustration onpage 229, has a complicated reproductive cycle. Study the illustration to understand this complicated cycle.228Chapter 20READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.How are sac fungi important?3. What ascomycote mightyou encounter every day?NameDateClassSection20.2The Diversity of Fungi, continuedA Stalk and capAbove ground, a mushroom consistsof a stalk that supports a cap.B GillsCapThe undersides of most caps have thinsheets of tissue, called gills, which containbasidia that produce basidiospores.Wind disperses mature spores.GillsC Spore germinationWhen a basidiospore germinates,it produces hyphae of eithermating strain + or –.StipeBasidiosporesBasidiumBasidiospore+ Mating type – Mating typeMeiosisBasidiaF Spore productionCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.In the basidia, haploidnuclei fuse.
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