ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Review Questions and Answers		AP BIOLOGY: Chapter Four Outline INTRODUCTION Earth Formed 4.5 Billion Years Ago Oldest rocks 4.3 billion years Oldest microfossils are 3.5 billion years old Possible Origins of Life on Earth Extraterrestrial origin, panspermia Special creation, supernatural or divine forces Evolution from inanimate matter Content of biological examination Only scientific origin permitting testable hypotheses via fossils Examine Early Earth Prior to Appearance of Life fig 4.1 THE ORIGIN OF ORGANIC MOLECULES: CARBON POLYMERS Nature of Early Earth Composition of original atmosphere Primarily nitrogen gas, carbon dioxide, water Secondarily hydrogen sulfide, ammonia, methane Debatable whether free hydrogen gas was present Termed a reducing atmosphere Requires less energy to form carbon molecules Free oxygen gas absent Significant geothermal energy available fig 4.2 Presently shielded from UV radiation by ozone layer Prompted chemical reactions of atmospheric materials Formed complex molecules Stored energy in covalent bonds Life may have originated in deep-sea hydrothermal vents Experimental Recreation of Origins Miller and Urey hypothetically repeated process fig 4.3 Similar atmosphere over liquid water Temperature 100%C with sparks of energy Methane formed carbon compounds fig 4.4 Formaldehyde, hydrogen cyanide Further combined into formic acid, urea Later experiments produced carbon compounds Amino acids: glycine, alanine, valine, proline, glutamic, aspartic acids Adenine produced, one of the bases found in DNA and RNA Debate regarding origin of first organic molecules RNA first, heredity required for consistent production of biomolecules Supported by discovery of ribozymes RNA in ribosomes also has an enzymatic function Proteins first since nothing can be replicated without enzymes Nucleic acid units too complex to form spontaneously Have created synthetic nucleotides that replicate and "mutate" CHARACTERISTICS OF LIVING THINGS Must Define Life to Determine Whether or Not It Exists Potential characteristics: value as a definition Movement: not descriptive of only life fig 4.5 Sensitivity: some life not apparently responsive fig 4.6 Death: meaningless concept Complexity: describes nonlife also Definition of life must not only be necessary, possessed by all life but sufficient, possessed by only life Accepted Characteristics of Life Cellular organization fig 4.7 Growth and metabolism Assimilation of energy Creation of carbon-carbon covalent bonds Metabolic energy transferred via phosphate bonds Reproduction fig 4.8 Heredity Characteristics of Preliving Coacervates Phospholipid molecules enclosing fluid Accumulate more molecules to grow and divide Lack genetic mechanisms to change next generations Structure reflects only present environment Adaptations to environment not passed on Genetic change is essence of evolution THE ORIGIN OF THE FIRST CELLS Spherical Protocells Aggregations of microspheres 1-2 mm diameter Arise from amino acids or fats suspended in water Internal fluid very different from external environment Molecules have hydrophobic regions Possess growth-promoting metabolic reactions Divide into daughter cells with same characteristics as parent Oparin's Theory of Primary Abiogenesis Called first cell-like structures protobionts Led to Urey-Miller experiments THE EARLIEST CELLS Fossils Found in Ancient Rocks fig 4.9 Microfossils closely resemble present day bacteria Single-celled , 1 to 2 microns in diameter No external appendages Little evidence of internal structures Simple organisms like these called prokaryotes Name means "before nucleus" Eukaryotes with nuclei evolved later Prokaryotes collectively called bacteria Living Fossils Unusual organisms found in uncommon environments Different from present day bacteria in form and metabolism Little evolution of forms living in unchanging habitats Are living relics of early life Biochemically diverse bacteria Found in fossilized stromatolites Archaebacteria Methane-producing bacteria Grow only in oxygen-free environment Anaerobic, poisoned by oxygen Convert CO2 and H2 into CH4 (methane) Superficially resemble other bacteria Structure of membrane and cell wall significantly different Absence of peptidoglycan in cell walls Unusual lipids in cell membranes Function of genes more like eukaryotes than eubacteria Eubacteria Strong cell walls, simpler gene architecture Capture light energy Transform it into chemical bond energy Utilize a variety of pigments Cyanobacteria (blue-green algae) are an important group Possess chlorophyll pigment Decisive role in increasing oxygen in Earth's atmosphere Increased ozone, protection from ultraviolet radiation Some caused accumulation of limestone deposits The Origin of Modern Bacteria Most forms of early life died out Modern bacteria derived from only a few early forms Bacteria were only life on Earth for 2 billion years fig 4.10 THE APPEARANCE OF EUKARYOTIC CELLS All Fossils Older Than 1.5 Billion Years Are Structurally Similar fig 4.11 Visually Different Microfossils Appear After 1.5 Billion Years fig 4.12 Much larger size, as much as 60 microns Have internal membranes, some contain membrane-bound structures Possess thicker walls, branched filaments or spines New Cells Called Eukaryotes Name means "true nucleus" Includes all organisms other than bacteria Rapidly evolved to produce diverse life forms fig 4.13 Pelomyxa, a Model Early Eukaryote Has nucleus, but lacking microtubules, divides like a prokaryote Lacks mitochondria, but has bacteria that perform same function Margulis' Endosymbiotic Theory Evolution of eukaryotes involved symbiosis with prokaryotes Examples: mitochondria, chloroplasts, flagella, centrioles Eukaryotes Reproduce Sexually Promotes genetic recombination Evolved process of meiosis Diversity Promoted by Multicellularity Single cell organisms formed colonies Division of labor established within a colony CLASSIFICATION OF LIVING THINGS Classification Schemes Have Evolved With Changing Information Current Six Kingdom System Kingdom Archaea: prokaryotic, archaebacteria Kingdom Monera: prokaryotic, eubacteria Kingdom Protista: eukaryotic, unicellular heterotrophs or photosynthesizers Kingdom Fungi: eukaryotic, multicellular, non-motile heterotrophs Kingdom Plantae: eukaryotic, multicellular, terrestrial photosynthesizers Kingdom Animalia: eukaryotic, multicellular, motile heterotrophs IS THERE LIFE ON OTHER WORLDS? Nature of The Earth as a Planet Reflects Its Life Forms Farther from sun Colder temperature, water in the form of a solid Chemical reactions slower Carbon compounds brittle Closer to sun Warmer temperature Chemical bonds and carbon compounds less stable Evolution of carbon-based life Limited by temperature, dependent on distance to sun Affected by size of earth and gravitational pull Mathematical Likelihood for Similar Conditions Billions of stars resembling sun 10% with planetary systems Chance for proper size and distance allows 1015 earth-like planets Evolution of Different Life Forms Could evolve life from other chemicals Silicon chemistry similar to carbon chemistry