1.5 The origin of cells Flashcards
What is spontaneous generation?
The supposed production of living organisms from nonliving matter
In 1860 what did Louis Pasteur design an experiment to disprove?
Louis Pasteur designed an experiment to disprove the prevailing theory of spontaneous generation of cells.
What method did Louis Pasteur use in his experiment? What were the results? What was the conclusion?
1) Louis Pasteur made a nutrient broth by boiling water containing yeast and sugar.
2) he placed samples of broth in flasks with long necks and then melted the glass of the neck and bent it into a swan necked shape which do not allow external particles to pass through
3) he boiled the broth to kill any existing micro organisms, sterilizing the broth
4) he broke off the swan neck from flask one, exposing the nutrient broth to air
5) he left a swan neck from flask two as it was
Results: nutrient broth turned cloudy in flask 1 indicating microorganism growth. In flask 2, the nutrient broth remained clear.
Conclusion: for growth of microorganisms to occur, a source of contamination is needed, rejecting the hypothesis of spontaneous generation
What were the condition of earths prebiotic atmosphere?
- no free oxygen (was ‘reducing’)
- abundant volcanic activity
- frequent electrical storm/lightning
- strong UV levels reaching earth surface
- contain methane, ammonia and hydrogen
What did Miller-Urey experiment (1953) demonstrate? What did Miller and Urey find in the mixture?
How was heat represented?
What were the three gas is contained within their stimulated probiotic atmosphere?
How was lightning represented?
It demonstrated chemical evolution – forming complex organic molecules from simpler in organic molecules found on prebiotic earth.
Heat - thermal energy from the sun, geothermal heat and volcanoes
Methane, hydrogen, ammonia
Electrical discharges were sparked through the gas and represent lightning
They found amino acids (13 of the 20 naturally occurring amino acids) and other organic biomolecules.
What did Miller and Urey’s experiment allowed for?
the formation of amino acids
Why were polymers prevented from forming in Miller and Urey’s experiment?
The condition used also tended to hydrolyse the bonds preventing polymers from forming
What was a possible site for the origin of the first carbon compound and where does the energy come from?
- Around deep sea thermal vents. These are cracks in the earth’s surface, characterised by gushing hot water carrying reduced inorganic chemicals such as iron sulphide.
- These chemicals represent readily accessible supplies of energy, a source of energy for the assembly of these carbon compounds into polymers.
How did membranes form to package the organic molecules?
If phospholipids are other amphipathic carbon compounds were among the first carbon compounds, they would have naturally assembled into bilayer.
Experiments have shown that the bilayers readily form vesicles for assembling the plasma membrane of a small cell. This would have allowed different internal chemistry from that of the surroundings to develop.
How are living organisms made? What was believed to be the genetic material in an earlier phase in evolution? Why?
Living organisms currently have genes made of DNA. To replicate DNA and be able to pass genes on to offspring, enzyme are needed. But genes are needed for enzymes to be made.
The solution may have been an earlier phase in evolution when RNA was the genetic material. It can store information in the same way as DNA but it is both self replicating and can itself act as a catalyst.
What is the theory of Endosymbiosis? How does it work?
It is the theory that eukaryotic cells arose from prokaryotic cells.
Prokaryotic cells with infolded membranes (for making ATP, or containing chlorophyll) invaded, or were engulfed by other prokaryotes, but not digested. As the invaded prokaryotes’s membrane folded inwards around the invading cell, this produced the double membrane of what are now mitochondria and chloroplast.
The larger prokaryotic cell and the smaller cell were in a symbiotic relationship in which both of them benefited. This is known as a mutualistic relationship. Natural selection therefore favorite source that had develop this endosymbiotic relationship.
How did the larger prokaryotic cell and a smaller cell benefit from each other?
- small prokaryotes that can carry out photosynthesis evolve into chloroplast - they receive reactions from the host cell and provide the host cell with glucose
- the smaller prokaryotes that can carry out aerobic respiration evolved into mitochondria - they receive glucose from the host cell and converted to glucose into energy for the host cell to use.
