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1.5 IB Bio

The Origin of Cells

When did life begin? -Earth is 4.5 billion years old -It took approx .5 billion years for the Earth to cool to form a crust -As early as 4 billion years ago early cells existed
Cell Theory questioned in the origin of cells -All cells come from pre-existing cells
The four/five steps in creating the first cells (Step One) 1. The non-living synthesis of simple organic molecules from a mixture of any three of methane, hydrogen, ammonia and water vapor.
The four/five steps in creating the first cells (Step Two) 2. The assembly of these molecules into polymers
The four/five steps in creating the first cells (Step Three) 3. The origin of self-replicating molecules that make inheritance possible
The four/five steps in creating the first cells (Step Four) 4. The packaging of these molecules into membranes with an internal chemistry different from their surroundings.
The four/five steps in creating the first cells (Step Five) 5. The development of binary fission of these protocells.
Symbiosis An association between two or more species.
Endosymbiosis theory (Eukaryotes are formed from prokaryotes) -Mitochondria of eukaryotes came from aerobic bacteria -Chloroplasts evolved from primitive autotrophic prokaryotes -Both were taken into larger heterotrophic cells by endocytosis -Eukaryotes then formed membranes that could contain the prokayotes
Evidence to Endosymbiosis Theory -Mitochondria and chloroplasts have DNA that is separate from the cells nuclear DNA -This DNA is similar to prokaryotic DNA (not associated with proteins) -Mitochondria and chloroplasts have small 70S ribosomes (regular eukaryotic ribosomes are 80S)
Evidence to Endosymbiosis Theory- Part 2 -Mitochondria and chloroplasts have double membrane
Prior to Louis Pasteur (1822-1895) -Notion of spontaneous generation was commonly accepted -This proposed that life is continuously being spontaneously created where no life previously existed
Louis Pasteur's Experiment Step One -Started with two flasks and a nutrient broth in each
Louis Pasteur's Experiment Step Two -Bent the necks of the flasks into "S" shapes
Louis Pasteur's Experiment Step Three -Boiled the broth to kill any existing microbes
Louis Pasteur's Experiment Step Four -Broke off the swan neck from the 1st flask only, exposing the nutrient broth to air from above. -In flask 2, dust particles remained near the tip of the swan neck
Louis Pasteur's Experiment Step Five -The broth in the broken flask quickly became cloudy (a sign of microbial life) -The unbroken flask remained clear
Created by: averyschwarz



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