1. Phylum
    2. 1. Classification of Animals
    2. Protozoa
    3. Porifera
    4. Coelenterata
    5. Platyhelminthes
    6. Nemathelminthes
    7. Annelida
    8. Earthworm
    9. Arthropoda
    10. Cockroach
    11. Mosquito
    12. Honey bee and Silk moth
    13. Mollusca
    14. Echinodermata
    15. Hemichordata
    16. Chordata
    17. Pisces
    18. Amphibia
    19. Frog
    20. Reptile
    21. Aves
    22. Mammalia
    23. Rabbit bone
  2. Animal Behaviour and Adaptation
    3. 24. Animal behaviour
    25. Animal adaptation
    26. Migration
  3. Developmental Biology
    4. 27. Development of Animals
    28. Development of Frog
  4. Human Biology
    5. 29. Tissues
    30. Sense organs
    31. Digestive system
    32. Circulatory system
    33. Respiratory system
    34. Nervous system
    35. Endocrine system
    36. Reproductive system
    37. Excretory system
    38. Skeletal system
    39. Basic concept of Immunology
    40. Human diseases
  5. Evolutionary Biology
    6. 41. Origin of Life
    42. Organic Evolution
    43. Theories of Evolution
    44. Evolution of Human beings
    45. Horse Evolution
Evolutionary Biology
41. Origin of Life
ORIGIN OF LIFE
Origin of Universe
Big-bang Theory
Proposed by
Abbe Lemaitre (1931)
Age
Approximately 10^10 years
Description
Current universe
About 20 billion years old with huge clusters of galaxies
Galaxies
Contain stars and clouds of gas and dust
Event
Singular huge explosion unimaginable in physical terms
Aftermath
Expansion
Universe expanded causing temperature to decrease
Element formation
Hydrogen and Helium formed later
Galaxy formation
Gases condensed under gravitation to form present-day galaxies
Solar system formation
Formed about 4.6 billion years back in the milky way galaxy
Origin of Earth
Formation
About 4.6 billion years back in the milky way galaxy
Early conditions
Atmosphere
Initially absent
Surface composition
Covered by Methane(CH4), Ammonia(NH3), Water(H2O) and Carbon dioxide(CO2) released from molten mass
UV radiation effects
Water breakdown
UV rays split water into Hydrogen(H2) and Oxygen(O2)
Hydrogen
Lighter Hydrogen escaped
Oxygen reactions
Combined with Methane (CH4) and Ammonia (NH3) to form Water (H2O), CO2 and others
Early events
Bombardment period
Subjected to heavy bombardment with large comets and meteorites
Ocean vaporization
Heat from impacts periodically vaporized oceans
Life appearance
Appeared 0.5 billion years after Earth's formation (~4 billion years ago)
Introduction
Timeline
Life appeared 0.5 billion years after Earth's formation (~4 billion years ago)
Significance
Considered a unique event in the history of universe
Early Earth
Could not support life when first formed
Life organization
Organized from non-living materials between Earth's formation and first fossils
Nature of life
Chemical phenomenon with chemical origin
Research
Since 1950, full-time research on origin of life studies in several laboratories worldwide
Theories on Origin of Life
Special creation theory
Support
Most of the world's major religions and civilizations
Religious texts
Bible and Hindu philosophy
God created all living organisms
Key proponents
Father Suarez
Spanish priest, greatest supporter of special creation theory
Archbishop Ussher
Claimed God created the world in October 4,004 BC (specific timeline provided)
Abiogenesis/Spontaneous generation
Historical belief
Ancient Chinese, Babylonians and Egyptians believed life could arise spontaneously from non-living material
Examples
Frogs
From damp Earth
Mice
From putrefied matter
Insects
From dew
Maggots
From decaying meat
Van Helmont's experiment
Claimed young mice could arise from wheat grains in a dark cupboard with a moist dirty shirt (1557-1644)
Biogenesis (Life from life)
Opponents of spontaneous generation
  1. Francesco Redi (1668)
  2. Abbe Lazzaro Spallanzani (1767)
  3. Louis Pasteur (1867)
Key experiments
Redi experiment
Disproved spontaneous generation of flies from rotting meat
Spallanzani experiment
Method
Sterilized nutritive broth by boiling meat in sealed flasks
Conclusion
Air carried microorganisms
Pasteur's swan-neck experiment
Method
Used flasks that allowed air but not microorganisms
Conclusions
  1. Demonstrated biogenesis
  2. Finally disproved spontaneous generation (1861)
  3. Didn't explain first life form
  4. Discovered role of bacteria in fermentation and anaerobic bacteria
Contributions
  1. Germ theory of disease
  2. Principle of sterilization (Pasteurization)
Cosmozoic theory/Spore theory
Proponents
  1. Richter (1865)
  2. Arrhenius (1908)
Concept
Life transferred between planets as spores
Modern support
Some astronomers believe primitive life came via meteorites (Panspermia)
Evidence cited
  1. UFO sightings
  2. Cave drawings of rocket-like objects
  3. 1996 NASA discovery of possible bacterial remains in Martian rock
Catastrophism theory
Proposed by
Georges Cuvier (1796)
Concept
Simultaneous extinction and creation of life from inorganic material via natural cataclysms
Oparin-Haldane theory
Proponents
  1. Alexander Oparin (1924, expanded 1936)
  2. J.B.S. Haldane (1929)
Key concepts
Primitive atmosphere
Reducing atmosphere without free oxygen
Modern atmosphere
Composition
  1. 78% molecular nitrogen
  2. 21% free oxygen (from photosynthesis)
  3. 1% argon
  4. 0.03% carbon dioxide
Nature
Strongly oxidizing
Essential condition
Presence of water
Energy sources
  1. Solar radiation
  2. Lightning
  3. Volcanic ash
Chemical evolution
First compounds
Methane, Ethylene, Acetylene (hydrocarbons)
Primordial soup
Organic compounds accumulated in oceans (Haldane's 'hot dilute soup')
Polymerization
Formed proteins, carbohydrates and fats
Experimental support
Miller-Urey experiment (1953)
Apparatus
Spark discharge apparatus
Gases used
Methane(CH4), Ammonia(NH3), Hydrogen(H2) (2:1:2) and Water(H2O)
Results
  1. Synthesized 15 amino acids including Glycine, Alanine, Valine, Proline, Aspartic acid
  2. Demonstrated formation of organic monomers
Melvin-Calvin experiment (1951)
Method
Irradiated CO2 and H2O in cyclotron
Products
  1. Formic acid
  2. Succinic acid
  3. Oxalic acids
Recognition
Nobel Prize (1961)
Macromolecule evolution
Polymer formation
Through dehydration synthesis
Hypotheses
RNA-first hypothesis
Concept
RNA could perform both genetic and enzymatic functions
Evidence
  1. Ribozymes (catalytic RNA discovered by Thomas Cech and Sidney Altman, Nobel 1989)
  2. Some viruses have RNA genes
Implication
Early 'RNA world'
Protein-first hypothesis
Proponent
Sidney Fox
Findings
  1. Amino acids polymerize abiotically to form proteinoids
  2. Proteinoids form microspheres with cellular characteristics
Cairns-Smith's hypothesis
Concept
Clay facilitated simultaneous polymerization of proteins and nucleic acids
Mechanism
Clay attracts organic molecules and contains catalytic metals (iron, zinc)
Protocell evolution
Definition
Structure with lipid-protein membrane capable of energy metabolism
Formation theories
Fox's microspheres
Lipids associate with proteinoids forming membranes
Oparin's coacervates
Concentrated macromolecules forming complex units that absorbed organic substances
Characteristics
Anaerobic chemoheterotrophs
First cells
Features
  1. Membrane boundary
  2. Heterotrophic fermenters with enzyme activity
  3. Capable of reproduction
Oldest fossils
3.5 billion years old, resembling heterotrophic bacteria
Prokaryote evolution
Timeline
Evolved before eukaryotes
Early types
  1. Chemoheterotrophs (fermentation)
  2. Anaerobic chemoautotrophs
  3. Photosynthetic bacteria (initially only photosystem I)
Key developments
  1. Cyanobacteria developed oxygenic photosynthesis (two photosystems)
  2. Archaeospheroides barbertonesis (oldest fossil, 3.2 billion years)
  3. Oxygen as first major pollutant
Genetic mechanisms
  1. Binary fission (limited variability)
  2. Mutations as primary source of variation
Eukaryotic cell origin
Oldest fossils
1.5 billion years old
Energy metabolism
Aerobic cellular respiration
Classification history
Haeckel (1868) proposed kingdoms Monera (prokaryotes) and Protista (unicellular eukaryotes)
Evolutionary significance
Led to protists, fungi, plants and animals
Extraterrestrial life
Potential location
Mars (no conclusive evidence found)