Reading Essentials for Biology Glencoe (794133), страница 48
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What are the three environments where archaebacteria live?________________________________________________________________________200Chapter 18Archaebacteria live mainly in extreme habitats where there isusually no free oxygen supply. There are three different types ofarchaebacteria. The first type lives in oxygen-free environmentsand produces methane gas.
They live in marshes, lake bottoms,and the digestive tracts of some mammals, such as cows. Theyalso are found at sewage disposal plants, where they help with thebreakdown of sewage.A second type of archaebacterium lives only in water with highconcentrations of salt, such as in Utah’s Great Salt Lake and theMiddle East’s Dead Sea. A third type lives in the hot, acidicwaters of sulphur springs and thrives near cracks deep in theocean floor.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Diversity of ProkaryotesNameDateClassSection18.2Archaebacteria and Eubacteria, continuedWhat are eubacteria?Eubacteria, the other kingdom of bacteria, live in less severeplaces than do archaebacteria. When people speak of bacteria,they are usually referring to the more common eubacteria.
Onetype of eubacteria is heterotrophic. Remember that a heterotrophicorganism cannot make its own food. Heterotrophic eubacterialive almost everywhere and use organic molecules as their foodsource. Some bacterial heterotrophs are parasites, obtainingtheir nutrients from living organisms. Others are saprophytes—organisms that feed on dead organisms or organic waste.A second type of eubacterium is the photosynthetic autotroph.These eubacteria use the sun’s energy to make food for themselves.Cyanobacteria are photosynthetic autotrophs. They can be foundin ponds, streams, and moist areas of land.A third type of eubacterium is the chemosynthetic autotroph.These bacteria also make organic molecules that are their food,but they do not need sunlight to do so. Instead, they breakdown and release the energy of inorganic compounds containingsulfur and nitrogen.
This process is called chemosynthesis(kee moh SIHN thuh sus).2. Identify the process thatbacteria use to make foodfrom the breakdown ofinorganic compounds.________________________________________________________________________Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What is a bacterium?Although tiny, a bacterial cell has all the structures necessary tocarry out its life functions. The illustration on page 202 showsmany of the important parts of a cell. One of the most importantparts might be the cell wall.
The cell wall protects the bacteriumby preventing it from bursting.Most bacteria live in an environment where there are morewater molecules outside the cell than inside the cell. That meanswater is always trying to get inside the bacterial cell. If there isan opening in the cell wall, water enters the cell and it bursts.Scientists have used that important fact to develop medicines thatfight bacterial infections.If you have a bacterial infection, a doctor will often give youan antibiotic. Some antibiotics work by preventing bacteria frommaking cell walls. Water enters the cells, and they burst and die.The first antibiotic discovered was penicillin.READING ESSENTIALSChapter 18201NameDateClassSection18.2Archaebacteria and Eubacteria, continuedB Cell wallA cell wall surrounds the plasma C Chromosomemembrane.
It gives the cell itsA single DNA molecule, arrangedshape and prevents osmosis fromas a circular chromosome and notbursting the cell.enclosed in a nucleus, containsmost of the bacterium’s genes.A CapsuleSome bacteria have a sticky gelatinouscapsule around the cell wall. A bacteriumwith a capsule is more likely to causedisease than a bacterium without a capsule.D FlagellumSome bacteria have long,whiplike protrusions calledflagella (singular, flagellum)that enable them to move.G Plasma membraneA plasma membrane surroundsthe cell and regulates whatenters and leaves the cell.E PlasmidA few genes are located in asmall circular chromosomepiece called a plasmid.
A bacteriummay have one or more plasmids.Some bacteria have pili—extensionsof their plasma membranes. A hairlikepilus helps a bacterium stick to a surface.It is also like a bridge through or on whichtwo bacteria can exchange DNA.How can different bacteria be identified?Scientists use different ways to identify bacteria. From a medical point of view, it is important to identify bacteria because someantibiotics can destroy only particular bacteria. Gram staining is acommon method of identifying bacteria by checking for differencesin the structure of their cell walls. When bacteria are Gram stained,some will turn purple and others will turn pink.
Bacterial cells thatturn purple are called Gram-positive. Gram-negative cells turnpink. Based on the results, doctors know which antibiotic to use.Shape is another way to identify bacteria. The three most common shapes are spheres, rods, and spirals. The scientific term fora sphere-shaped bacterium is coccus; for a rod-shaped bacterium,bacillus; and a spiral-shaped bacterium, spirillum.Scientists also use the growth pattern of bacterial cells to identifythem. They use the prefix diplo– to refer to cells that grow in pairs.202Chapter 18READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.F PilusNameDateClassSection18.2Archaebacteria and Eubacteria, continuedThey use the prefix staphylo– to refer to cells that resemble grapeclusters, and they use the prefix strepto– to refer to cells that growin long chains.
Using this information you can probably pictureStaphylococcus bacteria.ConjugationCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.How do bacteria reproduce?All the cells you have studied to this point reproduced by mitosis or meiosis. However, bacteria do not have a nucleus or a pairof chromosomes. Bacteria have only one circular chromosomeand some smaller circular pieces of DNA called plasmids.Bacteria reproduce asexually in a process called binary fission.First a bacterium makes a copy of its chromosome.
Now there aretwo chromosomes in the cell. The cell begins to grow larger and,eventually, the chromosomes move to opposite ends of the cell.A wall begins to form in the middle. This separates the cell intotwo new cells. The two new cells are genetically identical.Bacteria also reproduce sexually using conjugation(kahn juh GAY shun).
This method produces bacteria with awhole new genetic combination. Use the illustration of the bacteria at the right to help you understand the process. The pilus(plural, pili) is the bridge-like structure that one bacterium uses toconnect to another bacterium. The first bacterium transfers all orpart of its chromosome to the second bacterium through thepilus. Now the second bacterium has a mix of genetic material.This bacterium reproduces by binary fission and now there aretwo cells with the new genetic material.3.
Identify On the linesbelow list the two waysthat bacteria can reproduce. Draw a circle aroundthe method that producesgenetically identical cells.________________________________________________Adaptations in BacteriaBacteria have adapted in some amazing ways. Based on fossil evidence, some scientists propose that bacteria were probably amongthe first organisms to undergo photosynthesis. Recall that photosynthesis produces both food and oxygen. As oxygen levels inEarth’s atmosphere increased, some bacteria probably adapted touse it for respiration.
Bacteria that must have oxygen to surviveare called obligate aerobes. Not all bacteria adapted to use oxygen,however. Bacteria that die in the presence of oxygen are calledobligate anaerobes. There is a third type of bacteria that can livewith or without oxygen.Bacteria have been around for millions of years. As you remember from previous sections, the environment of Earth has changeda lot in that time. Bacteria have a survival mechanism when facedwith unfavorable environmental conditions. They produceendospores.
An endospore is a tiny structure that contains aREADING ESSENTIALS4. What type of bacteriamust have oxygen inorder to survive?________________________________________________________________________Chapter 18203NameDateClassSection18.2Archaebacteria and Eubacteria, continuedbacterium’s DNA and a small amount of cytoplasm. Theendospore has a tough outer covering that resists drying out,temperature extremes, and harsh chemicals.The endospore rests until environmental conditions improve.Then, similar to a seed, the endospore germinates, or produces acell that begins to grow and reproduce. Endospores can stay inthe resting state for thousands of years before they germinate.Endospores can create problems for people.
One endospore isproduced by the bacterium that causes botulism, a type of foodpoisoning. Another is produced by the bacterium that causesanthrax. Botulism can appear in food that has not been properlyprocessed during canning. If the endospore for botulism is present, it grows in the closed environment of the can and producesa toxin, which is a powerful and deadly poison.Anthrax is caused by a bacterium that lives in soil. Cattle orsheep occasionally contract anthrax.
If people handle the animals,they may get a harmless anthrax infection of the skin. Sometimesthe anthrax endospores become airborne. If many endospores areinhaled into the warm moist environment of the lungs, they cangerminate, causing an often-fatal illness. Because anthrax canspread easily through the air, it has been used as a biologicalweapon to intentionally harm people.The Importance of BacteriaMost people tend to think of bacteria in terms of illness anddisease. However, there are actually only a few disease-causingbacteria compared to the number of harmless and beneficial bacteria. In fact, we could not survive without bacteria.What do bacteria do for us?5.
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