Origin of Cells (1.5)

Question 1

Miller and Urey Experiment

Answer 1

Miller and Urey recreated the 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 analysed and found to contain traces of simple organic molecules

Question 2

Abiogenesis

Answer 2

The theory that living cells arose from non-living matter.

Question 3

Biogenesis

Answer 3

The principle that living things only arise from other living things by reproduction (not spontaneous generation)

Question 4

Louis Pasteur’s experiment

Answer 4

Pasteur set up two flasks of broth and attached swan-necked tubes to both. He then boiled the broth to kill any microbes. After the broth had been sterilised, Pasteur broke off the tube from one of the flasks, exposing this broth to the air. The broth in this flask turned cloudy, indicating the presence of microbial life (carried from dust in the air). However, the broth in the flask with the tube attached remained clear as the dust was unable to travel against gravity into the flask. So Pasteur showed that without the introduction of dust, no life arose proving that all cells arise from pre-existing cells and do not spontaneously generate.

Question 5

Endosymbiotic Theory

Answer 5

Ancestral prokaryote cells evolved to develop features of mitochondria and chloroplast. Large prokaryote cells engulfed these cells and formed a symbiotic relationship. Over time the prokaryote cell evolved to form a eukaryote cell.

Question 6

Evidence for the Endosymbiotic Theory

Answer 6

• Have their own circular DNA which has genetic material containing prokaryotic features.
• Have ribosomes in the 70S form like prokaryote cells. Eukaryote cells have 80S form.
• Double membrane. The inner membrane contains proteins in prokaryote cells.
• Same size as bacteria (prokaryote cells) and susceptible to antibiotics.
• Can only be produced by the division of existing mitochondria or chloroplasts. Fission like process.