Origin and Evolution of Life — Class 12 Maharashtra HSC Biology revision notes
A 9-page visual revision sheet for Origin and Evolution of Life, written for Class 12 Maharashtra HSC Biology. Formulas, diagrams and the traps that cost marks, laid out to be read the night before rather than the term before. Free, and it opens inside CapCompass.
Page 1 as PDF
Origin and Evolution of Life in one look
from a hot dilute soup to Homo sapiens, one selection pressure at a time
Four Old Theories of Origin
- Special creation: oldest, religious belief, no scientific proof: a supernatural power created all life
- Cosmozoic / Panspermia: life descended to Earth as spores (cosmozoa); doesn't explain life's origin elsewhere
- Spontaneous generation (Abiogenesis): life arose directly from non-living matter; disproved by Louis Pasteur's swan-neck flask experiment
- Biogenesis: life only comes from pre-existing life, by reproduction; explains continuity, not the FIRST origin
Chemical Evolution (Self-Assembly Theory)
- life arose on Earth through chemicals reacting over a very long time
- first formulated by Haeckel, developed by Oparin (1924, Russia) and Haldane (1929, Britain)
- the Universe formed about 20 billion years ago (Big Bang, Georges Lemaitre, 1931)
- Earth formed about 4.6 billion years ago, from a rotating cloud of gas and dust
- heavier elements sank to form the core
- Earth's primitive atmosphere was reducing: rich in hydrogen, carbon, nitrogen, sulphur, no free oxygen
Chemical Evolution, Step by Step
- hydrogen reacted with other elements to form CH4, NH3, H2O and H2S as the atmosphere cooled
- steam condensed into heavy rainfall, forming rivers, lakes and oceans
- with no ozone layer, UV radiation reached the surface directly
- energy from UV, lightning and volcanic activity drove condensation, polymerisation, oxidation, reduction
- this formed simple organic molecules: monosaccharides, amino acids, purines, pyrimidines, fatty acids, glycerol
- these collected as Haldane's "hot dilute soup" or "primitive broth"
- stable because there was no free oxygen or enzymes to break it down
- polymerisation built complex molecules: polysaccharides, fats, proteins (via protoproteins), nucleosides, nucleotides
- protein formation is considered a landmark step
- nucleotides joined into nucleic acids (RNA, DNA)
- these acquired self-replicating ability, the fundamental property of life
- nucleic acids plus organic/inorganic molecules formed protobionts: prebiotic aggregates with some living-system properties
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What this Origin and Evolution of Life sheet covers
- Four Old Theories of Origin
- Special creation
- Cosmozoic / Panspermia
- Spontaneous generation (Abiogenesis)
- Biogenesis
- Chemical Evolution (Self-Assembly Theory)
- Chemical Evolution, Step by Step
- Coacervates vs Microspheres
- Coacervates (Oparin)
- Microspheres (Sidney Fox)
- First Cell, and the Experimental Proof
- RNA World Hypothesis
- Before Darwin: Lamarck and Weismann
- Darwin's Route to 'Origin of Species' (1859)
- Darwinism, Five Postulates
- 1. Overproduction
- 2. Struggle for existence
- 3. Organic variations
- 4. Natural selection
- 5. Speciation
- Evidence Darwin Cited, and Where He Fell Short
- Mutation Theory (Hugo de Vries, 1901)
- Darwin's Variation vs de Vries's Mutation
- Darwinian variation
- Mutation (de Vries)
- Modern Synthetic Theory
- Sources of Genetic Variation
- Gene mutation
- Genetic recombination
- Gene flow
- Genetic drift
- Chromosomal aberration
- Three Patterns of Natural Selection
- Hardy-Weinberg Equilibrium
- allele frequencies
- genotype frequencies
- AA : Aa : aa
- Isolation, the Third Pillar
- Reproductive Isolation: Pre- vs Post-Mating
- Pre-mating (pre-zygotic)
- Post-mating (post-zygotic)
- Adaptive Radiation
- Homologous vs Analogous Organs
- Homologous
- Analogous
- Vestigial Organs and Molecular Evidence
- Fossils and Connecting Links
- The Planet's Timeline, a Few Landmarks
- Speciation, By Mode
- Geological Time, in Brief
- Human Evolution, the Line of Descent
- Human Evolution, Milestone by Milestone
- Terms Worth Keeping Straight
- Traps that cost marks
- Tricks that save time
How CapCompass uses this sheet
These notes are not a standalone PDF. CapCompass plans Biology chapter by chapter against your real exam dates and free hours, and when the plan reaches Origin and Evolution of Life the sheet opens inside the study block itself — at the page covering the sub-topic that block is on, with the timer still running. Revision arrives at the moment the plan says revise, instead of having to be gone looking for.
More Biology Class 12 revision notes
- Biodiversity, Conservation and Environmental Issues
- Biotechnology
- Control and Co-ordination
- Ecosystems and Energy Flow
- Enhancement of Food Production
- Human Health and Diseases
- Inheritance and Variation
- Molecular Basis of Inheritance
- Organisms and Populations
- Plant Growth and Mineral Nutrition
- Plant Water Relation
- Reproduction in Lower and Higher Animals
- Reproduction in Lower and Higher Plants
- Respiration and Circulation