Beginnings of Life Flashcards
What is the cell theory?
- All things are composed of cells
- All cells come from pre-existing cells
- Cells are the smallest unit of life
What were early Earth’s conditions?
- Atmosphere was ‘reducing’
- Gases included H2, N2, CO, CO2
- Lacked O2
- Crust was very hot; cooled and solidified
- Rain stripped mineral salts from rocks
- Early seas formed in depressions in the crust
What is spontaneous generation?
- Living creatures could arise from non-living matter, and such pressures were commonplace and regular
- Hypothesis: certain forms could arise from inanimate matter (maggots from dust)
What was the Louis Pasteur experiment?
Hypothesis: if cells could arise from non-living substances then they should appear spontaneously in broth.
Method:
1. Two experiments were set up
2. Added nutrient broth to both flasks with a swan neck in one
3. Broth was boiled to kill any existing microbes
4. Left to observe
Results:
1. Swan neck flask had no microbe growth
2. Control flask contained microbe growth
Conclusion: cells are not generated spontaneously, but come from contamination of the air
What is biogenesis?
- Living things only arise from other living things by reproduction and not spontaneous generation
- Chemical process that contributed to initial formation of biological life required specific conditions to proceed (high temps, electrical discharge, chemical reactions)
- Cells can only be formed by the division of pre-existing cells
What is abiogenesis?
Living things arise from non-living matter in 4 key stages:
- Form simple organic molecules from inorganic molecules
- Simple molecules assembled into more complete molecules
- Complete molecules can self-replicate
- Molecules packaged into membranes which identify as primitive cell
What are the proposed origins for life on Earth?
Volcanoes: Gas composition contains high levels of fixed nitrogen (primitive metabolism)
Outer space comets: Derived from other planets. Contain organic matter
Shore: Alternation of wet and dry conditions
Hydrothermal vents: Superheated water released from Earth’s crust. Hydrogen rich fluids
What was the Miller and Urey experiment?
Tried to recreate early Earth conditions in the laboratory in 1953.
Simulated: the atmosphere, lightening, volcanic activity
Recreated the postulated conditions of pre-biotic Earth using a closed system of flasks and tubes.
What is an extinctinction vs a mass extinction?
Extinction: permanent loss of a species
Mass extinction: sudden widespread extinction
What can cause mass extinctions?
- Habitat degradation
- Predation
- Disease
- Large natural disasters
What are the 5 major extinction events?
- Ordovican-Silurian: 450 mya, 60-70% loss
- Late Devonian: 370 mya, over 75% loss
- Permian: 250 mya, 96% loss
- Triassic: 200 mya, 50% loss
- Cretaceous: 65 mya, 80% loss
What is the endosymbiotic theory?
- A cell which lives within another cell.
- The engulfed cell remains undigested as it provides benefit.
- Prokaryote grows in size and develops folds in its membrane to maintain an efficient SA:Vol ratio
What is evidence for the endosymbiotic theory?
- Both have double membrane
- Both have own DNA
- DNA is naked and circular
- Both replicate by binary fision
What are the three domains of life?
- Bacteria
- Archea
- Eukaryote
What are the taxa?
Domain Kingdom Phylum Class Order Family Genus Species
