Reading Essentials for Biology Glencoe (794133), страница 39
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However, in themid-1880s, Louis Pasteur designed an experiment that disprovedthe spontaneous generation of microorganisms.Pasteur used a specially designed glass bottle that allowed air toenter the bottle, but kept microorganisms out. There was a brothwith nutrients in the bottle. As long as Pasteur kept the microorganisms out, the broth remained clear.Pasteur’s experiment showed that microorganisms come fromother microorganisms. This led to the concept of biogenesis(bi oh JEN uh sus), the idea that living things come only fromother living things.2.
Describe How did Pasteurdevelop the concept ofbiogenesis?________________________________________________________________________Origins: The Modern IdeasFor more than 100 years biologists have accepted the idea of biogenesis. But that still does not answer the question: How did lifebegin on Earth? There are many theories, none of which have beenproven scientifically.
Scientists continue to look into theories andtest hypotheses about what conditions existed on early Earth.Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.How did simple organic molecules form?Scientists hypothesize that two things happened before lifecould appear on Earth. The first is that there had to be organicmolecules—molecules containing carbon. The second is that theorganic molecules must have formed into more complex molecules such as proteins, carbohydrates, and nucleic acids.
Theseare the materials that are absolutely necessary for life.Scientists think that the early atmosphere of Earth did not contain any free oxygen. Instead, the atmosphere was made of watervapor, carbon dioxide, nitrogen, methane, and ammonia. How didthis mixture combine and form the organic molecules that arefound in all living things today?In the 1930s, a Russian scientist named Alexander Oparin suggested that lightning striking Earth, heat from the sun, andEarth’s own heat started chemical reactions using substances inEarth’s atmosphere. The chemical reactions made small organicmolecules that ended up in the ocean when it rained. This turnedthe ocean into an environment in which life could start. Thishypothesis is illustrated in the figure at the top of page 160.3.
What two things had tohappen before life couldappear on Earth?________________________________________________How was Oparin’s hypothesis tested?In 1953, two American scientists, Stanley Miller and HaroldUrey, tested Oparin’s hypothesis. They mixed the elementsREADING ESSENTIALSChapter 14159NameDateClassSectionThe Origin of Life, continuedEnergy from the sun and lightningstrikes molecules in the sea.4.
Analyze What happenswhen amino acids areheated? (Circle yourchoice.)a. They becomeprotocells.b. They become proteins.c. They melt.Molecules combineto form simpleorganic molecules.Larger molecules continueto form, making simpleamino acids.thought to be in Earth’s early atmosphere—water vapor, ammonia,methane, and hydrogen gases—and added electricity. It becamehot. When the mixture cooled, it contained organic moleculessuch as amino acids and sugars. This result provides support forOparin’s hypothesis.Scientists then tested whether it was possible for more complexmolecules to form from the organic molecules.
Many experimentswere performed. Scientists discovered that when amino acids areheated, they turn into proteins. Many scientists were convincedthat complex organic molecules had formed in small pools ofwarm water on Earth.What is a protocell?In 1992, Sidney Fox caused complex molecules to turn intoprotocells. A protocell is a large, organized structure, surroundedby a membrane. It is able to grow and divide. Growth and division are considered life activities.The Evolution of CellsIn an earlier chapter you learned that prokaryotes are one-celledorganisms that do not have internal membrane-bound structures.The first life-forms may have been prokaryotes that evolved fromprotocells.
There was no oxygen available in the atmosphere atthis time. So the first life-forms were able to survive without it.That means they were anaerobic. They probably were not able tomake their own food but survived on the organic material in theocean. Gradually they changed into organisms similar to presentday archaebacteria, which do make their own food. Archaebacteria(ar kee bac TEER ee uh) live in harsh environments such as160Chapter 14READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.14.2NameDateClassSection14.2The Origin of Life, continueddeep-sea vents or hot springs. They make their food by chemosynthesis. In chemosynthesis, organisms turn compounds, such assulfur compounds, into food.What changes did photosynthesis cause?The next organisms to develop may have been prokaryotes thatcould undergo photosynthesis.
Photosynthesis releases oxygen.Oxygen began to enter the atmosphere. Organisms that use oxygen began to develop. The fossil record shows that 2.8 billionyears ago there was an increase in the variety of prokaryotes.Oxygen in the atmosphere had another effect. The sun’s raysconverted the oxygen to ozone molecules. This ozone layershielded organisms from harmful ultraviolet radiation. That madeit possible for even more complex organisms to evolve.5. What were two resultsof oxygen in theatmosphere?________________________________________________Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What new organisms evolved?The more complex organism that evolved was a eukaryote.A scientist named Lynn Margulis has a theory about how eukaryotic cells may have evolved.
According to this theory, prokaryotesmay have consumed bacteria. Some of these bacteria evolved intomitochondria, which released energy for the cell. Other typesevolved into chloroplasts. Present day mitochondria and chloroplasts share similarities with bacteria. The DNA of chloroplastsand mitochondria resembles the DNA of prokaryotes instead ofeukaryotes. The figure below illustrates this process.AA prokaryote ingestedsome aerobic bacteria. Theaerobes were protectedand produced energy forthe prokaryote.Aerobic bacteriaBOver a long time,the aerobes becomemitochondria, nolonger able to liveon their own.MitochondriaCSome primitiveprokaryotes also ingestedcyanobacteria, whichcontain photosyntheticpigments.CyanobacteriaDThe cyanobacteriabecome chloroplasts,no longer able tolive on their own.ChloroplastsPlantcellProkaryoteAnimal cellREADING ESSENTIALSChapter 14161NameDateClassSection14.2The Origin of Life, continued◗ After You ReadMini Glossaryarchaebacteria (ar kee bac TEER ee uh): chemosynthetic prokaryotes that live in deep seavents and hot springsprotocell: large, ordered structure, enclosed by amembrane that carries out some life activities, such as growth and divisionbiogenesis (bi oh JEN uh sus): idea that livingthings come only from other living thingsspontaneous generation: mistaken idea thatliving things can arise from nonlivingmaterials1.
Read the key terms and definitions in the Mini Glossary above. Highlight the two key termsthat describe ideas about the origin of living things. On the lines below, explain which ideacame first and why it was replaced by the other idea.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________2. Place the following events in the order in which they occurred on the vertical time line.
Thefirst event and the last event have already been entered on the time line.Protocells developOceans contain organic moleculesOrganisms use photosynthesisComplex organic molecules formProkaryotes appearOrganisms use chemosynthesisEukaryotes develop3. Select one of the time line events. On a separate sheet of paper, write three sentencesexplaining the importance of this event.Visit the Glencoe Science Web site at science.glencoe.com to findyour biology book and learn more about the origin of life.162Chapter 14READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Ozone layer developsNameDateClassSection15.1 Natural Selection and theEvidence for Evolution◗ Before You ReadSC.D.1.4.4 The student knows that Earth’s systems and organisms are the result of a long,continuous change over time.
SC.F.2.4.3 The student understands the mechanisms ofchange (e.g., mutation and natural selection) that lead to adaptations in a species andtheir ability to survive naturally in changing conditions and to increase species diversity.Also covers SC.F.1.4.2In biology, evolution means that populations of a species change over time. In this section you willlearn about Charles Darwin and his theory of evolution. Skim the Read to Learn section below andfind three important facts about Darwin.
Write those facts on the lines below. After you have writtenyour facts, highlight the one you think is the most important.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Charles Darwin and Natural SelectionEvolution describes the way populations change over time.
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