Topic 1.5 Origin of Cells

Question 1

Miller-Urey Experiment

Answer 1

Stanley Miller and Harold Urey recreated the postulated conditions of pre-biotic Earth using a closed system of flasks and tubes

• Water was boiled to vapour to reflect the high temperatures common to Earth’s original conditions
  The vapour was mixed with a variety of gases (including H2, CH4, NH3) to create a reducing atmosphere (no oxygen)
• This mixture was then exposed to an electrical discharge (simulating the effects of lightning as an energy source for reactions)
• The mixture was then allowed to cool (concentrating components) and left for a period of ~1 week
• After this time, the condensed mixture was analyzed and found to contain traces of simple organic molecules

Question 2

Pasteur’s experiments

Answer 2

The law of biogenesis is largely attributed to Louis Pasteur, who demonstrated that emergent bacterial growth in nutrient broths was due to contamination by pre-existing cells

• Broths were stored in vessels that contained long tubings (swan neck ducts) that did not allow external dust particles to pass
• The broths were boiled to kill any micro-organisms present in the growth medium (sterilisation)
• Growth only occurred in the broth if the flask was broken open, exposing the contents to contaminants from the outside
• From this it was concluded that emergent bacterial growth came from external contaminants and did not spontaneously occur

Question 3

Evidence of Endosymbiosis

Answer 3

M- Membranes (double membrane bound)
A- Antibiotics (susceptibility)
D- Division (mode of replication)
D- DNA (presence and structural composition)
R- Ribosomes (size)