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Option D Evolution
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Exam of 11 pages for the course Option D Evolution at Option D Evolution (Option D Evolution)
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Option D Evolution, Option D Evolution
D1 Origin of life on Earth
D.1.1 Describe four processes needed for the spontaneous origin of life on Earth
The non-living synthesis of simple organic molecules (i.e. amino acids from
inorganic molecules such as water, carbon dioxide and ammonia)
The assembly of these molecules into polymers (more complex molecules)
The origin of self-replicating molecules that made inheritance possible
The packaging of these molecules into membranes with an internal chemistry
different from their surroundings
D.1.2 Outline the experiments of Miller and Urey into the origin of organic compounds
Experiments showed that simple organic molecules such as amino acids can be produced in
abiotic conditions. By passing steam through a mixture of methane, hydrogen and ammonia, this
was possible. Miller and Urey essentially investigated the theory that organic compounds could
have formed spontaneously on Earth. They were able to recreate past conditions by mixing
ammonia, methane and hydrogen to form a reducing atmosphere. Electrical discharge and
boiling and condensation of water simulated lightning and rainfall. One week later, clear water
turned into murky brown. This revealed many organic compounds including 15 amino acids.
They concluded that organic compounds could have formed spontaneously on Earth before
living organisms existed.
D.1.3 State that comets may have delivered organic compounds on Earth
D.1.4 Discuss possible locations where conditions would have allowed the synthesis
of organic compounds
Miller and Urey’s experiment suggests that organic compounds could have been
synthesized by chemical reactions in the atmosphere and in water on the surface of
the Earth.
In the oceans where there are hydrothermal vents with chemicals from the rocks below.
There is an unusual chemical composition around the vents which could have allowed for
spontaneous synthesis from the first organisms evolved.
Another location involves an extraterrestrial origin for organic compounds. Scientists
have shown that organic compounds and proto-cells could have formed in cold
interstellar space. Meteorites, comets or interplanetary dust could have delivered them
to Earth.
D.1.5 Outline two properties of RNA that would have allowed it to play a role in the
origin of life
RNA could have played a significant role in the origin of life prior to the presence of DNA and
enzymes; thereby probably preceding DNA. This was the case because DNA is a molecule which
was too complex to have formed in earlier protobionts1. Gradual evolution would have required
simpler intermediate stages instead of the whole mechanism evolving at once. Two properties are
(both include ribozymes):
Catalysis— RNA catalyzes a broad range of chemical reactions. It could therefore have taken the
role that is carried out by proteins (enzymes) in the organisms that now exist on Earth.
1 Initial structures during the origin of life which shows at least one property of life. A collection of organic molecules surrounded by a
membrane/membrane-like structure.
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