8.4 Life on Earth 1. Analysis of the oldest sedimentary rocks provides evidence for the origin of life Identify the relationship between the conditions on early Earth and the origin of organic molecules Early earth contained no ozone layer so large amounts of UV radiation reached the earth, the reason for the absence of no ozone layer was their was little free oxygen. The volcanic emissions filled the atmosphere with methane, ammonia, hydrogen, carbon dioxide, carbon monoxide and small amounts of water vapour. The violent electrical storms and acidic rain formed the present warm and mineral - rich oceans. There are only two possible ways organic molecules could have formed either - formed on earth from simpler molecules - arrived from the cosmos Discuss the implications of the existence of organic molecules in the cosmos for the origin of life on Earth Meteorites and comets have been studied and have identified 74 amino acids. Certain types of meteorites such as the "carbonaceous chondrites" contain carbon - rich compounds and that life may have occurred from meteorites arriving to primitive earth, thus the theory of Panspermia. Describe two scientific theories relating to the evolution of the chemicals of life and discuss their significance in understanding the origin of life Theory 1 - Organic molecules arrived from the cosmos Certain types of meteorites such as the "carbonaceous chondrites" contain carbon - rich compounds. Theory says that these meteorites, the compounds in them, may have formed to simple organisms. Yet however the presence of these compounds are not sufficient enough to create life or form organic molecules Theory 2 - Chemicals for life formed on Earth Haldane and Oparin suggested that Earth had all the necessary basic chemical components for life on Earth. They hypothesised that the complex organic molecules could have been created from UV radiation, electrical discharges, and heat. They also said that the continued synthesis led to the formations of polypeptides from amino acids and a range of molecules. Oparin also worked on the heterotrophic hypothesis where by the first organisms were not autotrophic but heterotrophic that fed on the organic material around them Discuss the significance of Urey and Miller's experiments in the debate on the composition of the primitive atmosphere Urey and Miller set up a simulation of primitive earth. A mixture of hydrogen, ammonia, and methane in the form of steam was continuously electrically discharged for a week. The experiment resulted in a solution containing a number of amino acids and hydroxy acids which are vital components for living things. Urey and Miller’s experiment supported Oparin and Haldane’s theories on the origin of life, which showed that organic material, could be formed by raw materials. Identify changes in technology that have assisted in the development of an increased understanding of the origin of life and evolution of living things Technology for the understanding of the origin of life: Deep sea equipment allows exploration of remote environments Infra red observations and simulations allows to gather and explore evidence from space Aircrafts can now collect space dusts Technology for the evolution of living things Radioactive isotopes can accurately date the fossils etc. Electron microscopes reveal comparison between early life and present day. 2. The fossil record provides information about the subsequent evolution of living things Fossils are the remains of life forms that have become trapped in sediments and have been preserved. There are three types of fossils: originals, moulds and casts. Originals are fossils that have preserved organic parts which eventually hardens into sedimentary rock. The mould is when the organic part is decomposed and leaves a cavity of it. The cast is when the mould is filled with materials which eventually harden into rock, and this cast is of the original organism. Fossilisation occurs under these three conditions: - Quick burial in sediments - Prevention of decay - Undisturbed Identify the major stages in the evolution of living things, including the formation of: - organic molecules - membranes - procaryotic heterotrophic cells - procaryotic autotrophic cells - eucaryotic cells - colonial organisms - multicellular organisms Organic Molecules - Theories of Oparin and Haldane + The theories of Miller and Urey. Organic molecules formed in the oceans in primitive Earth and at some stage the simpler organic molecules joined to become more complex. Membranes - Membranes are needed to protect the interior workings e.g. organelles, nucleus. The organic molecules protected by membranes evolved into nucleic acids and were capable of replicating. Heterotrophic cells – First procaryotes non – membrane bound organisms. These procaryotic cells obtained energy from organic molecules that existed in the primitive environment. Autotrophic cells - These procaryotic cells obtained energy through photosynthesis and chemosynthesis Eucaryotic cells – These cells have membrane bound organelles. These organisms used procaryotes as organelles and were membrane bound organelles. Colonial Organisms - These were multicellular organisms, may have originated after cell division to form an aggregation of similar cells or a colony. Multicellular Organisms - Specialised cells which are dependant on each other in the colony Describe some of the palaeontological and geological evidence that suggests when life originated on Earth Palaeontological Evidence Earth is believed to be about 4.5 billions years old. The oldest evidence of life was found to be similar to cyanobacteria found stromatolites that are about 3.5 billion years old in southern Africa and Australia. However these fossils are photosynthetic suggesting that life started prior to that of 3.5 billion years ago. Geological Evidence Ancient rocks contained chemical evidence that the metabolism of cyanobacteria was underway. The first primitive cells were heterotrophic; they obtained energy by consuming organic compounds. The evolution of photosynthesis, led to the production of oxygen however the oxygen was not first built up in the atmosphere but in rocks. These oxidised rocks are called ancient banded iron, these rocks can be dated with the range of levels of oxygen locked inside it showing the approximate time over which plant life forms evolved. Explain why the change from an anoxic to an oxic atmosphere was significant in the evolution of living things As oxygen levels rose, photosynthetic organisms became more abundant, while the anaerobic organisms were inhibited due to the presence of oxygen. The formation of the ozone layer protects the Earth from UV radiation Explosion of diverse forms of plants and animals The evolution of photosynthesis and respiration Discuss ways in which developments in scientific knowledge may conflict with the ideas about the origins of life developed by different cultures Different cultures and religious in the world have their own ideas about life, it maybe quite different to the scientific evidence In biblical creationism different organisms were made for specialised environments at the same time, the organisms that were created have not changed nor are they related. 3. Further developments in our knowledge of present day organisms allows for better understanding of the origins of life and the processes involved in the evolution of living things Describe the technological advances that have increased knowledge of procaryotic organisms SEM (Scanning Electron Microscopy) and TEM (Transmission Electron Microscopy) have assisted the understanding of the structure of cyanobacteria Improvements in microscopes, better images of small cells Describe the main features of the environment occupied by one of the following and identify the role of this organism in its ecosystem: - Archaea - Eubacteria - Cyanobacteria - Nitrogen – fixing bacteria - Methanogens - Deep – sea bacteria Procaryotic Cell Environment Role in ecosystem Archaea Hostile environments Carry out inorganic reactions for chemical energy Eubacteria All habitats, known for diseases Plays a vital role in the many of them cause recycling in an ecosystem Cyanobacteria Mainly in marine environments Carry’s out photosynthesis Nitrogen – fixing bacteria Live mutualistically on plants Converts nitrogen to ammonium ions that can be converted to amino acids in the plants Methanogens Anaerobic conditions Use hydrogen compounds and carbon dioxide to produce energy for themselves and release methane as a waste product Deep – sea bacteria Boiling undersea vents of Basis of food web, use sulphur volcanoes compounds to derive energy 4. The study of present – day organisms increases our understanding of past organisms and environments Explain the need for scientists to classify organisms There is a diverse amount of living organisms and their behaviour and in order for biologists to study them, they have developed classification systems. Classification helps to describe, identify, communicate about, observe trends and explain relationships in things such as living organisms. Describe the selection criteria used in different classification systems and discuss the advantages and disadvantages of each system 2 Kingdom system 3 Kingdom system 5 Kingdom system Kingdom groups Plants Monera (procaryotic Monera Animals organisms) Protista (unicellular Plants organisms) Animals Fungi Plants Animals Selection criteria Plants: Autotrophic, Monera: Procaryotic Monera: Procaryotic cell wall Plants: Eucaryotic, Protista: Unicellular, Animals: photosynthetic Eucaryotic Heterotrophic, no cell Animals: Eucaryotic, Fungi: Eucaryotic, walls heterotrophic multicellular Plants: Eucaryotic, heterotrophic Animals: Eucaryotic, heterotrophic Advantages Works well for familiar Separating out Distinguishing between organisms procaryotes fungi Disadvantages Some unicellular Some unicellular Protista contains organisms possess eucaryotic organisms widely differing characteristics both possess both animal organisms animal and plant like and plant like No difference between characteristics procaryotic and eucaryotic cells Explain how levels of organisation in a hierarchical system assist classification The system of graded levels of organisations help classification because it provides a framework in which the different levels of similarity and difference can be reflected. 1. Kingdom 2. Phylum Number in group 3. Class decreases, organisms 4. Order 5. Family become more similar 6. Genus 7. Species Discuss, using examples, the impact of changes in technology on the development and revision of biological classification systems Classification was based on external characteristics; new technology has allowed comparisons at cellular and molecular levels. Biochemical techniques have enabled us to obtain sequences of amino acids in protein molecules and the bases in DNA. Describe the main features of the binomial system in naming organisms and relate these to the concepts of genus and species Binomial System – Two part system Dichotomous keys – Keys are used to separate the organisms into two groups which then branch off into sub – groups. Binomial Systems 1. The first word has a capital letter which represents the genus to which the organism belongs to. 2. The second word represents the species within the genus to which the organism belongs to. 3. Both printed in italics Examples: Petauroides volans – Genus - Petauroides // species – volans Banksia coccinea – Genus – Banksia // species - coccinea Dichotomous Keys 1. Features must be clear and accurate 2. Features must be observable Identify and discuss the difficulties experienced in classifying extinct organisms Reconstruction of fossils is difficult and is changed to suit new evidence. Descriptions of features of extinct species such as colour, body covering and habitat may be very interpretative. It is also difficult to tell whether the fossils were of the same or different species if the species is extinct. Explain how classification of organisms can assist in developing an understanding of present and past life Earth Classification helps to compare and contrast different organisms over a range of criteria; also classification systems help to represent evolutionary relationships. This system applies to present and past life forms.