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Liza Dinh March 26, 2012 Period 5 Chapter 26: The History of Life on Earth AP Biology Study Guide (Worksheet) Ms. Turner INTRODUCTION TO THE HISTORY OF LIFE 1. Explain how the histories of Earth and life are inseparable. The histories of Earth and life are inseparable because geological events affect biological evolution; similarly, organisms cause major chemical changes on Earth. Taken together, such changes provide a grand view of the evolutionary history of life on Earth. 2. Describe the major events in Earth's history from its origin up to about 2 billion years ago. In particular, note when Earth first formed, when life first evolved, and what forms of life existed up until about 2 billion years ago. There is scientific evidence that Earth and the other planets of the solar system formed about 4.6 billion years ago, condensing from a vast cloud of dust and rocks that surrounded the young sun. For the first few hundred million years, Earth was bombarded by huge chunks of rock and ice left over from the formation of the solar system. The collision generated enough heat to vaporize the available water and prevent seas from forming. This phase likely ended about 3.9 billion years ago. The first atmosphere was probably thick with water vapor, along with various compounds released by volcanic eruptions, including nitrogen and its oxides, CO2, methane, ammonia, H2, and hydrogen sulfide. 3.5 to 4 billion years ago (bya), cellular life appeared. 3.5 bya, oldest fossils (stromatolites, layered rocks that form when certain prokaryotes bind thin films of sediment together) first appeared 2-3 bya, Archaea and Bacteria diverged 2.5-2.7 bya, oxygen gas appeared in large amounts 1.7 bya oldest fossils of eukaryotes first appeared 3. Describe the timing and significance of the evolution of photosynthesis. Oxygen gas is produced during the water splitting step of photosynthesis. When oxygenic photosynthesis first evolved, the free oxygen gas it produced probably dissolved in the surrounding water until it reached a high enough concentration to react with dissolved iron. Once all of the dissolved iron had precipitated additional oxygen gas dissolved in the water until the seas and lakes became saturated with oxygen gas. After this occurred, the oxygen gas finally began to gas out of the water and enter the atmosphere. This change left its mark in the vesting of iron rich terrestrial rocks, a process that began about 2.7 billion years ago. This chronology implies that bacteria similar to today's cyanobacteria (oxygen releasing, photosynthetic bacteria) originally that well before 2.7 billion years ago. The amounts of atmospheric oxygen gas increased gradually from about 2.7 to 2.2 billion years ago, but then shot up relatively rapidly to more than 10% of its present level. In searching of its chemical forms, oxygen attacks chemical bonds and can inhibit enzymes and damaged cells. As a result of the rising concentration of atmospheric oxygen gas probably doomed many prokaryotic groups. Some species survived in habitats that remain anaerobic. 4. Describe the timing of key events in the evolution of the first eukaryotes and later multicellular eukaryotes. Describe the snowball-Earth hypothesis. 2.1 bya, oldest definite eukaryote fossils appeared 2.7 bya, origin based on chemical traces: endosymbiosis (a model which posits that mitochondria and plastids were formerly small prokaryotes that begin living within larger cells) 1.5 bya, common ancestors of multi-cellular eukaryotes first lived Snow-ball Earth: the hypothesis suggests that most life would have been confined to areas near deep sea vents and hot springs or to equatorial regions of the ocean that lacked ice cover 5. Describe the timing of key evolutionary adaptations as life colonized land. 1 bya there was microscopic terrestrial life, then 500 mya… macroscopic terrestrial life took over. The sweeping changes in life on Earth revealed by fossils illustrate macrorevolution, the pattern of evolution over large time scales. Example: the origin of key biochemical processes such as photosynthesis, the emergence of the first terrestrial vertebrates, and the long time impact #history THE ORIGIN OF LIFE 6. Contrast the concept of spontaneous generation and the principle of biogenesis. Describe the biogenesis paradox and suggest a solution. Spontaneous generation: former belief that life can emerge from non-living Biogenesis: life by reproduction from pre-existing life Paradox: Where did the first living things come from? Solution: early Earth was different, very long periods of time were involved 7. Describe the four stages of the hypothesis for the origin of life on Earth. a. Abiotic synthesis of small organic molecules (amino acids and nucleotides) b. Polymerization (joining of these small molecules into macromolecules, including proteins and nucleotides) c. Packaging into membraneous protobionts (droplets with membranes that maintained an internal chemistry different from that of their surroundings) d. Self-replication molecules (eventually made inheritance possible) 8. Describe the contributions that A. I. Oparin, J. B. S. Haldane, and Stanley Miller made toward developing a model for the abiotic synthesis of organic molecules. Describe the conditions and locations where most of these early organic reactions probably occurred on Earth. Oparin and Haldane independently hypothesized that Earth’s early atmosphere was a reducing (electron-adding) environment, in which organic compounds could have formed from simple molecules. The energy for this organic synthesis could have come from lightning and intense UV radiation. Thirty years later, Miller and Urey tested the Oparin-Haldane Hypothesis by creating laboratory conditions comparable to those that scientists at the time thought existed on early Earth. It is likely in any case that small “pockets” of the early atmosphere – perhaps near volcanic openings –were reducing. Perhaps instead of forming in the atmosphere, the first organic compounds formed near submerged volcanoes and deep see vents, where hot water and minerals gush into the ocean from the Earth’s interior. 9. Describe the key properties of protobionts in the evolution of the first cells. Protobionts are aggregates of abiotically produced molecules If enzymes are included they metabolize and they have selective permeability. Discharging membrane potential means excitability. Protobionts can absorb and split into smaller units and lack hereditary traits. 10. Describe the evidence that suggests that RNA was the first genetic material. Explain the significance of the discovery of ribozymes. RNA, which plays a central role in protein synthesis, can also carry out a number of enzyme-like catalytic functions. RNA is central to information transfer in cells and can be copied abiotically. These RNA catalysts are called ribozymes. Some can make complementary copies of short pieces of RNA, provided that they are supported with nucleotide building blocks. Ribozymes have a variety of catalytic functions and pre-date enzymes. 11. Describe how natural selection would have worked in an early RNA world. Natural selection on the molecular level has produced ribosymes capable of self application in the laboratory. Unlike the doubled stranded DNA, which takes the form of a uniform helix, single stranded RNA molecules pursue a variety of specific three-dimensional shapes mandated by their nucleotide sequences. In a particular environment, RNA molecules with certain base sequences are more stable and replicate faster and with fewer errors and other sequences. The RNA molecules whose sequence this sequence is best suited to the surrounding environment and has greatest ability to replicate self believe the most to send it molecules. It's descendents will not be a single hour and a species but instead will be a family of sequences that different slightly because of copying errors. 12. Describe the evidence that suggests that life first evolved on the sea floor near deep-sea vents. The evidence that suggests that life first evolved on the sea floor near deep-sea vents include surface waters were heavily irradiated and bombarded. Abiotic syntheses of acetic acid, acetyl CoA, and sulfides of iron and nickel were present near vents as well. THE MAJOR LINEAGES OF LIFE 13. Describe the basis for R. H. Whittaker's five-kingdom system. The five kingdom system sets prokaryotes apart. Plants, animals and fungi are separated by structure, life cycles, modes of nutrition and the protista includes leftovers and misfits. 14. List, distinguish among, and describe examples from each of the five kingdoms. The five kingdoms are as such: Monera: prokaryotes Fungi: heterotrophs with external digestion Plants: multicellular autotrophs with tissues Animals: multicellular heterotrophs with internal digestion and tissues Protista: mainly unicellular eukaryotes 15. Compare the three-domain system and R. H. Whittaker's five-kingdom system of classification. The five kingdoms are explained as above, the six splits the monera into two domains. Plants Animals Protists Fungi Archaebacteria Eubacteria eukaryotes eukaryotes eukaryotes eukaryotes prokaryotes prokaryotes Multi-cellular Multi-cellular Uni-cellular Multi-cellular Uni-cellular Uni-cellular autotrophs heterotrophs Both* heterotroph autotrophs *both Whereas in the three domain system, the Archaea and Bacteria domains contain prokaryotic organisms. These are organisms that do not have a membrane bound nucleus. Eubacteria are classified under the Bacteria domain and archaebacteria are classified as Archaeans. The Eukarya domain includes the rest that do have a membrane bound nucleus. Archaea Domain Bacteria Domain Eukarya Domain Archaebacteria Kingdom Eubacteria Kingdom Protista Kingdom Fungi Kingdom Plantae Kingdom Animalia Kingdom VOCABULARY Stromatolite – See Question #2 Snow-ball Earth – See Question #4 Spontaneous generation – See Question #6 Biogenesis – See Question #6 Ribozyme – See Question #10 Protobionts – See Question #9 Three-domain system – See Question #15