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Biology 2 /SL Review Book Topic D.1:Origin of Life on Earth
Name _________________________
Review Book Topic D: Evolution
D.1 Origin of Life on Earth
Key facts
1. In order for life to be possible, four key problems had to be overcome on the early Earth.
a. Life as we know it is based on organic molecules such as amino acids, yet early Earth had only
inorganic matter.
b. In order to build more complex molecules like proteins, monomers (single molecules like amino
acids, simple sugars, and nucleotides) need to be connected together into polymers (long chains
such as polypeptides, such as polysaccharides, proteins, or RNA).
c. In order to be considered alive, things must be able to reproduce. DNA, the molecule most used
for the replication of living organisms, is a complex molecule that requires enzymes in its
formation. Also, to get polypeptides to form from DNA, RNA is needed.
d. Water tends to depolymerize molecules. Water dissolves many organic compounds, making it
difficult for molecules to become organized into polymers.
2. In 1953, Miller and Urey experimentally reproduced organic molecules from the atmospheric
components thought to have existed on pre-biotic Earth.
3. Miller and Urey’s formed organic molecules from the “primordial soup”, but they did not create life.
Amino acids cannot be described as alive.
4. The idea that life on Earth began in space is known as panspermia.
5. Comets (chunks of space ice) and meteorites can carry organic compounds. NASA studies reveal that
organic molecules can survive impact and the impact could help to polymerize some polypeptides
into amino acids. Earth underwent a major bombardment by comets about 4 billion years ago.
6. Hypotheses for the location and origin of organic molecules include formation in space and delivery
to Earth by comets, and formation in intertidal zones, deep-sea hydrothermal vents, or volcanoes on
Earth.
7. Evidence for the origin of organic molecules in space comes from studies of the spectral lines of
distant clouds of cosmic dust, which have been found to contain glycine, the simplest amino acid.
8. Alternating wet/dry conditions on flood plains or in intertidal zones might have provided an
environment for producing organic molecules. The drying of clay particles could have created
catalyzing reactions and formed early organic molecules.
9. Stromatolites, one of the oldest forms of life on Earth, live today in intertidal zones.
10. The eruption of water vapor, gases, and various minerals in volcanoes and the warmth of eruptions
could have provided conditions favorable to the formation of amino acids and sugars.
11. Deep sea hot water geysers called hydrothermal vents are rich in dissolved minerals are used by
symbiotic bacteria to make food for tube worms.
12. The study of the origin of life on Earth is a very young science and much work still needs to be done.
13. The prebiotic world did not contain enzymes which are needed for DNA replication; therefore, it is
unlikely that double-stranded DNA was the means of inheritance.
14. Single-stranded RNA can replicate itself without enzymes under certain conditions because it can
also act as a catalyst, helping certain chemical reactions the way enzymes do. Therefore, singlestranded RNA may have been the first molecule capable of passing along hereditary information.
15. Protobonts are structures that may have preceded the first living cells, providing an protected
internal environment for polynucleotides such as RNA.
Biology 2 /SL Review Book Topic D.1:Origin of Life on Earth
Name _________________________
16. Origins for protobonts include proteinoid microspheres (bubble-like structures formed when amino
acids spontaneously join together as polypeptide chains in drying clay) and coacervates (microscopic
spheres formed from lipids in water).
17. There was no oxygen on Earth 4 billion years ago; therefore, early forms of life on Earth were
anaerobic cells like bacteria.
18. About 3.5 billion years ago, certain bacteria developed the capacity to photosynthesize (make their
own food). Evidence for this is seen in rock formations rich in iron oxide. The bacteria converted iron
in ocean water to iron oxide.
19. Photosynthesis altered the composition of the atmosphere as oxygen was released as a waste
product. The non-photosynthetic bacteria that survived this “pollution” were those living in mud or
other places protected from the oxygen rich atmosphere.
20. Bacteria were the only organism on Earth from about 3.8 billion to 2 billion years ago, when the first
fossil cells of eukaryotes formed.
21. The endosymbiotic theory states that the first eukaryotic cells were formed when larger prokaryotic
cells ingested, but did not digest, smaller prokaryotic cells, in exchange for their services.
22. The endosymbiotic theory can explain how membrane-bound organelles such as mitochondria or
chloroplasts (which also) became part of another cell.
23. Mitochondria and chloroplasts have characteristics that make them more like independent
prokaryotes: They:
a. have a double membrane;
b. have their own naked circular DNA, just like prokaryotes
c. can perform protein synthesis using small ribosomes;
d. can make copies of themselves when more are needed.
24. Two problems with the endosymbiotic theory is the question of how the host cell passed on the
genetic information to offspring to synthesize the newly acquired organelle, and chloroplasts and
mitochondria cannot survive on their own outside the cell.
Further notes
Complete the following.
1. What four processes are needed for the spontaneous origin of life on Earth?
2. What is polymerization?
Biology 2 /SL Review Book Topic D.1:Origin of Life on Earth
Name _________________________
3. Outline Miller and Urey’s experiment into the formation of organic molecules.
4. Why are scientists studying comets in the effort to understand the origin of life on Earth?
5. List four environments where the synthesis of organic compounds could have occurred.
6. How might prebiotic polymers have solved the problem of depolymerization?
7. Outline the theory of endosymbiosis.
8. List four characteristics of mitochondria and chloroplasts that make them seem more like
independent prokaryotes.