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Section 14.2 Summary – pages 380-385. Origins: The Early Idea. Spontaneous generation — the idea that nonliving material can produce life. Disproved by Francesco Redi in the late 1600s. Section 14.2 Summary – pages 380-385. Spontaneous generation is disproved.
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Section 14.2 Summary – pages 380-385 Origins: The Early Idea • Spontaneous generation—the idea that nonliving material can produce life. • Disproved by Francesco Redi in the late 1600s.
Section 14.2 Summary – pages 380-385 Spontaneous generation is disproved • Redi’s well-designed, controlled experiment successfully convinced many scientists that maggots do not arise by spontaneous generation. Control group Time Time Experimental group
Section 14.2 Summary – pages 380-385 Pasteur’s experiments • In the mid-1800s, Louis Pasteur disproved the spontaneous generation of microorganisms. • Pasteur set up an experiment in which air, but no microorganisms, was allowed to contact a broth that contained nutrients.
Section 14.2 Summary – pages 380-385 Pasteur’s experiments The flask’s S-shaped neck allowed air to enter, but prevented microorganisms from entering the flask. Each of Pasteur’s broth-filled flasks was boiled to kill all microorganisms. Microorganisms soon grew in the broth, showing that they come from other microorganisms. Pasteur tilted a flask, allowing the microorganisms to enter the broth.
Section 14.2 Summary – pages 380-385 Pasteur’s experiments • Pasteur’s experiment showed that microorganisms do not simply arise in broth, even in the presence of air and, along with Redi’s experiments, provided evidence for the theory of biogenesis. • Biogenesis– the idea that living organisms come only from other living organisms.
Section 14.2 Summary – pages 380-385 Origins: The Modern Ideas • 2 developments probably preceded the appearance of life on Earth. • Simple organic (carbon-containing) must have formed. 2. These molecules must have become organized into complex organic molecules such as proteins, carbohydrates, and nucleic acids.
Section 14.2 Summary – pages 380-385 Simple organic molecules formed • In the 1930s, Alexander Oparin hypothesized that life began in the “primordial soup” of Earth’s early oceans. • He suggested that energy from the sun, lightning, and Earth’s heat triggered chemical reactions that produced small organic molecules from the substances present in the early atmosphere.
Section 14.2 Summary – pages 380-385 Formation of complex organic molecules • In 1953, Miller and Urey tested Oparin’s hypothesis by simulating the conditions of early Earth in the laboratory. • Miller and Urey’s experiments showed that if amino acids are heated without oxygen, they link and form proteins. • A similar process produces ATP and nucleic acids from small molecules.
Section 14.2 Summary – pages 380-385 Simple organic molecules formed Entry for hydrogen, methane, and ammonia gases Electrode High voltage source Condenser for cooling Boiling water Solution of organic compounds
Section 14.2 Summary – pages 380-385 The formation of protocells • Protocell - large, ordered structure, enclosed by a membrane. • Protocells carry out some life activities, such as growth and division. • Protocells have been produced by heating solutions of organic molecules. • The first forms of life may have been prokaryotes that evolved from a protocell.
Section 14.2 Summary – pages 380-385 The first true cells • Earth’s early atmosphere lacked oxygen • The first organisms were most likely anaerobic heterotrophs. • They fed off the organic molecules present in the early oceans.
Section 14.2 Summary – pages 380-385 Photosynthesizing prokaryotes • The earliest autotrophs were probably chemosynthetic like present-day archaebacteria. • The concentration of oxygen in Earth’s atmosphere increased due to the evolution of photosynthetic organisms. • The build up of oxygen set the stage for the evolution of aerobic respiration.
Section 14.2 Summary – pages 380-385 The endosymbiont theory • Complex eukaryotic cells probably evolved from prokaryotic cells. • Endosymbiont theory - eukaryotes evolved through a symbiotic relationship between ancient prokaryotes.
Section 14.2 Summary – pages 380-385 The endosymbiont theory A prokaryote ingested some aerobic bacteria. The aerobes were protected and produced energy for the prokaryote. Some primitive prokaryotes also ingested cyanobacteria, which contain photosynthetic pigments. Over a long time, the aerobes become mitochondria, no longer able to live on their own. The cyanobacteria become chloroplasts, no longer able to live on their own. Chloroplasts Cyanobacteria Mitochondria Aerobic bacteria Plant cell Prokaryote Animal Cell
Section 14.2 Summary – pages 380-385 Evidence for the endosymbiont theory • Chlorplasts and mitochondria have their own DNA. • Chloroplasts and mitochondria have ribosomes that are similar to the ribosomes in prokaryotes. • Chloroplasts and mitochondria also reproduce independently of the cells that contain them.
