Reading Essentials for Biology Glencoe (794133), страница 49
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How do bacteria helpplants?________________________________________________________________________204Chapter 18All living things need nitrogen. It is part of the proteins, DNA,RNA, and ATP of organisms. Nitrogen makes up about 80 percentof the atmosphere. Yet most living things, including plants, cannotdirectly use nitrogen from the air. This is where the bacteria comein. Some bacteria convert nitrogen from the air into ammonia. Theprocess is called nitrogen fixation. Other bacteria then convertammonia into forms of nitrogen that plants can use.
Bacteria arethe only organisms that can perform these chemical changes.Another important process that bacteria carry out is returningnutrients, both organic and inorganic, to the environment.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What happens to the endospore?NameDateClassSection18.2Archaebacteria and Eubacteria, continuedWithout bacteria to return nutrients to the environment, therewould not be any nutrients for the organisms at the bottom ofthe food chain. Recall that these autotrophs use the nutrientsin the food they make.
Without autotrophs producing oxygen asa byproduct of making food, there would not be oxygen in theatmosphere. So you can see that all of life depends on bacteria.In what other ways are bacteria helpful?Bacteria produce products that have distinctive flavors andsmells. Swiss cheese, yogurt, pickles, and sauerkraut are madewith bacteria.
Bacteria live in your intestines and produce vitamins and enzymes to help digest food.Earlier in this section you learned that antibiotics can kill bacteria that cause illnesses. Some bacteria are used to produce theantibiotics that kill other bacteria. Antibiotics have been an important factor in helping people live longer.6. Defend If someone tellsyou that bacteria are bad,how would you respond?________________________________________________Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.How does bacteria cause disease?Bacteria cause diseases in plants, animals, and humans.
Diseasecausing bacteria enter the human body through openings such asthe mouth. Bacteria are carried in air, food, and water. Sometimesbacteria enter the body through skin wounds.There are two ways bacterial diseases harm people. First, thegrowth of bacteria can interfere with the normal function of bodytissues. Second, the bacteria can release a toxin that directlyattacks the host.In the past, bacterial diseases had a greater effect on humanpopulations than they do now.
Antibiotics and improved healthcare systems have reduced the number of deaths caused by bacteria in the United States.________________________◗ After You ReadMini Glossarybinary fission: reproductive process in which onecell divides into two separate, geneticallyidentical cellschemosynthesis (kee moh SIHN thuh sus): autotrophic process in which organisms receiveenergy from the breakdown of inorganiccompounds containing sulfur and nitrogenREADING ESSENTIALSconjugation (kahn juh GAY shun): form of reproduction in some bacteria where one bacterium transfers all or part of its geneticmaterial to another through a bridge-likestructure called a pilusendospore: structure formed by bacteria duringlife-threatening conditions that containsDNA and a small amount of cytoplasm; hasa tough outer coveringChapter 18205NameDateClassSection18.2Archaebacteria and Eubacteria, continuednitrogen fixation: process by which bacteria convert nitrogen in the air into ammoniaobligate anaerobe: bacteria that die in the presence of oxygenobligate aerobe: bacteria that must have oxygento survivetoxin: poison produced by a bacterium1.
Review the terms and their definitions in the Mini Glossary. Circle the two words thatdescribe how bacteria reproduce. Then underline the word that describes the type of reproduction that results in bacteria with new genetic material. On the lines below describe howthat might be useful to bacteria.________________________________________________________________________________________________________________________________________________________________________2. Write the statements under the heading they best relate to.The Importance of BacteriaHarmfula.
Endospores germinate in human lungs.b. Provide nitrogen in a usable form for plantsc. Oxygen is a byproduct of making food.d. Cause infection in humanse. Flavor foodf. Create toxins3. Bacteria come in three different shapes: spheres, rods, and spirals. Write their scientificnames below each figure.SpheresRods1.2.12Spirals3.3Visit the Glencoe Science Web site at science.glencoe.com to findyour biology book and learn more about archaebacteria and eubacteria.206Chapter 18READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.HelpfulNameDateClassSection19.1 The World of ProtistsSC.F.1.4.2 The student knows that body structures are uniquely designed and adapted for their function.SC.G.1.4.1 The student knows of the great diversity and interdependence of living things.
Also covers SC.F.2.4.1◗ Before You ReadYou have learned all life is organized into six kingdoms. Without using your notes, name all six onthe lines below. Some of the organisms you will learn about in this section are plantlike, and someare animal-like. Still others have characteristics like fungi. Some of them were placed in differentkingdoms before they were finally classified as Kingdom Protista. As you read this section keep inmind how much variety there is in the world of protists.________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What is a protist?There is no such thing as a typical protist.
In fact, KingdomProtista contains the most diverse organisms of all the kingdoms.There are single-celled (unicellular) protists as well as manycelled (multicellular) protists. Some are microscopic, others arevery large. Some can make their own food, some cannot. Protistshave only one thing in common—they are all eukaryotes. Thatmeans most of their metabolic processes (chemical reactions)take place inside their membrane-bound organelles. Other thanthat, organisms classified as protists are quite different fromeach other.Some protists, called protozoans, seem to be like animalsexcept that they only have one cell.
Others, called algae, seem tobe like plants except they do not have roots, stems, or leaves.Algae are photosynthetic and autotrophic. Unicellular algae arethe basis of aquatic food chains and produce much of the oxygenin Earth’s atmosphere. Still other protists seem to be like fungiexcept that they do not have the same kind of cell walls that fungihave. You can see why protists have been difficult to classify.READING ESSENTIALSIdentify MainIdeas As you skim the section,draw a circle around the nameof each of the four groupsthat make up the protozoans.Chapter 19207NameDateClassSection19.1The World of Protists, continuedWhat is a protozoan?A protozoan is a unicellular animal-like protist. Protozoansare found in moist environments.
If you were to pick up wetdecaying leaves from the edge of a pond and place them undera microscope, you would discover the small world inhabitedby protozoans. Protozoans are a diverse group, but all feed onother organisms or dead organic matter. This means they areall heterotrophs.1. What are protozoans?________________________________________________________________________Diversity of Protozoans2. How are protozoansgrouped?Protozoans have been separated into four groups: amoebas, flagellates, ciliates, and sporozoans. Three of the groups—amoebas,flagellates, and ciliates—are grouped according to the way theymove. The fourth group, sporozoans, are grouped togetherbecause they are parasites.________________________________________________NucleusA As an amoeba approachesfood, pseudopodia formand eventually surroundthe food.208Chapter 19CytoplasmBAmoebas send out extensions of their plasma membranesto move and feed.
These extensions are called pseudopodia(sew duh POH dee uh). Amoebas can do this because they donot have a cell wall. The shape of the amoeba changes aspseudopodia form. The illustration below shows how an amoebafeeds on small organisms. The pseudopodia surround the food.Because amoebas live in moist places, nutrients dissolved inthe water can pass directly through the cell membrane and intothe organism.
Freshwater amoebas (and other protozoans) sometimes absorb too much water. They have pumps in the cytoplasmthat collect and pump out excess water. These pumps are calledcontractile vacuoles.PseudopodiaRemember thatprotozoans are foundin moist environments.Amoebas that live inthe sea are part ofplankton. Plankton isContractilean assortment ofvacuoleorganisms, many ofFood vacuolewhich are microscopic,The food becomesenclosed in afood vacuole.CDigestive enzymesbreak down the food,and the nutrientsdiffuse into the cytoplasm.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Can amoebas change their shape?NameDateClassSection19.1The World of Protists, continuedthat float in the ocean and form the base of the ocean’s foodchain.
One group of amoebas, called radiolarians, are an important part of marine plankton.Most amoebas reproduce by asexual reproduction. In asexualreproduction, the amoeba divides into two cells, producing identical offspring.How did flagellates get their name?Flagellates (FLAJ uh luts) got their name because they areprotists that have one or more flagella. Flagella are whip-likeorganelles that move from side to side and enable the protozoansto move about. Some flagellates are parasites. One type causessleeping sickness in humans.
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