Radiometric Dating
- Radioisotopes decay at a predictable rate
- By measuring the amount of radiation present now, and knowing the ‘half-life’ (the time it takes for the radiation to drop to half the previous level) of the isotope, the age can be calculated.
- This is how we know the age of the earth
- Carbon-14 dating
Electron Microscope
- Allows scientists to study ancient fossil cells in rocks and to make comparisons with ‘primitive’ cells that exist today
- Provides info about how ancient life forms lived and evolved
Biochemical Analysis and DNA technology
- Used to find the ‘relatedness’ of different living things
- Provides estimates of how long ago 2 related species divided from each other; evolutionary
- Have shown all life forms on earth are related → all living things evolved from one original type
- Shows which types are more closely or distantly related.
8.4.2 The fossil record and evolution
8.4.2.1 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/Urey-Miller.
- Organic molecules (sugars, amino acids, lipids) formed in the oceans in primitive Earth spontaneously and at some stage the simpler organic molecules joined to become more complex.
Membranes
- Needed to protect the interior workings e.g. organelles, nucleus.
- These were the precursors to cells
- The organic molecules protected by membranes evolved into nucleic acids and were capable of replicating.
Procaryotic Heterotrophic
- First procaryotes non-membrane bound organisms/nucleus.
- Obtained energy from organic molecules that existed in the primitive environment.
Procaryotic Autotrophic
- No membrane bound organelles/nucleus
- Obtained energy through photosynthesis and chemosynthesis
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During photosynthesis released O2 → highly toxic
- This caused major changes to chem. of earth and atmosphere
-
O2 reacted with chem. of oceans → when chem. exhausted began to build up in atmosphere
Eucaryotic
- Have membrane bound organelles/nucleus.
- Endosymbiotic theory – larger cells engulfed smaller cells; did not digest them. Engulfed heterotrophic cells became mitochondria. Some then engulfed photosynthetic bacteria (cyano) → chloroplasts
Colonial Organisms
- Multicellular organisms; may have originated after cell division to form an aggregation of similar cells or a colony.
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As O2 levels reached critical levels cells begin working cooperatively → allowed specialisation of cells
- Some cells became attached to each other forming filaments/ sheets
- Close association led to dependence → became multicellular organisms
Multicellular Organisms
- Specialised cells which are dependant on each other in the colony
- Close cooperation led to exchange of DNA → sexual reproduction
8.4.2.2 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.
- Oldest evidence of life was found to be similar to cyanobacteria → 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.
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The evolution of photosynthesis led to the production of O2 however the O2 was not first built up in the atmosphere but in rocks.
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These oxidised rocks are called ancient banded iron; these rocks can be dated with the range of levels of O2 locked inside it showing the approximate time over which plant life forms evolved.
8.4.2.3 Explain why the change from an anoxic to an oxic atmosphere was significant in the evolution of living things
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As O2 levels rose, photosynthetic organisms became more abundant, while the anaerobic organisms decreased due to the presence of O2.
- 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
8.4.2.4 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 may be quite different to the scientific evidence
- In biblical creationism different organisms were made at the same time; the organisms that were created have not changed nor are they related.
- Charles Darwin – theories on evolution; stating that the same rules of bio apply to man as well as any other creature
- Genetic technology – gives people opportunity to ‘play god’
- Modern technology looks at sequence of proteins/DNA btw organisms to determine extent of biological/evolutionary r/ships; prior – classification systems looked at structural characteristics → not always correct
8.4.3 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
8.4.3.1 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 living cells and allowing the visualisation of fossil remains
- Biochemistry – allows the study of reactions in cells
8.4.3.2 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
Roles of prokaryotes
- Converting nitrogen from atmosphere to forms where it can enter nutrient cycles
- Breaking down dead matter for recycling
- In dark environments bacteria convert chem. from volcanic eruptions into food
8.4.4 The study of present-day organisms increases our understanding of past organisms and environments
8.4.4.1 Explain the need for scientists to classify organisms
- Classification is not a scientific fact or theory. It is human’s attempt to order life on earth in such a way as to make sense of it.
- Allows for the arranging of living things into groups so they can be easily sorted.
- Allows for quick description
- Communication is precise and universal
- Similar organisms can be recognized
- Trend can be observed and compared
- Explains r/ships btw organisms
8.4.4.2 Describe the selection criteria used in different classification systems and discuss the advantages and disadvantages of each system
8.4.4.3 Explain how levels of organisation in a hierarchical system assist classification
The system of graded levels of organisation helps classification because it provides a framework in which the different levels of similarity and difference can be reflected. Organisms that are very different from each other are separated at the first level of classification.
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Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
8.4.4.4 Discuss, using examples, the impact of changes in technology on the development and revision of biological classification systems
- Classification was based on external characteristics (morphology)
- 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.
- Use of DNA technology allows for organisms to be compared. Also show evolutionary trends
8.4.4.5 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
- The first word has a capital letter which represents the genus to which the organism belongs to. Capital letter
- The second word represents the species within the genus to which the organism belongs to.
- Both printed in italics
Examples:
Petauroides volans – Genus - Petauroides // species – volans
Banksia coccinea – Genus – Banksia // species - coccinea
Dichotomous Keys
- Features must be clear and accurate
- Features must be observable
8.4.4.6 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, behaviour 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.
- Impossible to study their biochemistry or cell structure
8.4.4.7 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 and morphology relationships. This system applies to present and past life forms.