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Unit R072 How Scientific ideas have developed
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Proteins are produced in the cytoplasm of a cell – the jelly-like solution of chemicals where the cell stores
its food. However, DNA never leaves the cell’s nucleus, so how are new protein molecules produced?
Firstly a messenger molecule that can leave the nucleus is made. It’s a molecule called mRNA
(messenger RNA).
With the help of an enzyme, the DNA double helix is unzipped and then zipped up again. As this happens,
so does a series of chemical changes. The process, called transcription, is complex. Crucially, however,
it enables genetic information carried in DNA to be taken from the nucleus into the cytoplasm.
In the cytoplasm, mRNA attached to a large and complex molecule called a ribosome. Again, a series of
changes happen that leads to the construction of a protein. The process is called translation.
1.14 Explain the importance of mRNA.
1.15 What is the process of making a new protein called?
Evidence for evolution
Studying fossils tells us about
animals and plants and their
evolution over time.
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millions of years ago
Over generations all living things change, adapting to new and
changing environments. It has happened since life first began on
Earth and continues to happen. It’s called evolution.
Evidence for evolution comes from several sources.
Fossils, for example, enable us to ‘see’ organisms that were alive
millions of years ago. Scientists also have techniques that let
them work out the ages of fossils – in other words, how long ago
the organisms lived on Earth.
Fossils are the remains of these plants and animals, preserved
by natural processes. Some animals and plants were buried soon
after they died sinking in mud or buried in a sandstorm. They
turned into fossils, but it took millions of years.
More and more sediment (mud or sand) covered the remains,
pressing down on them. Over millions of years and high pressures,
changes happened that slowly turned the remains into a rock-like
copy of the original organism. So the fossil has the same shape as
the original organism, but is chemically more like a rock.
Only a small percentage of animals and plants formed fossils.
However, their fossil records are evidence for how living things on
Earth have changed. Organisms alive today evolved slowly from
simpler organisms.
Most fossil records of species are incomplete. Continuing finds of
new fossils are enabling gaps to be filled. Fossil records for the
horse and the camel show how both species evolved.
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Evolution of the horse.
1.16 Describe how fossils help scientists to understand evolution.
1.17 Explain why there are gaps in fossil records.
© 4science 2013
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Unit R072 How Scientific ideas have developed
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Selective breeding is done to produce animals and plants with desirable
characteristics. The practice goes back 2000 years. A scientific approach
to the practice was introduced by Robert Blackwell in the middle of the 18th
century during the British Agricultural Revolution. Selective breeding is used,
for example, to help produce better meat, milk, eggs, wheat and flowers.
The fact that the characteristics of animals and plants can be modified by
selective breeding over time is evidence for evolutionary change. Darwin used
it as one piece of evidence that supported his theory of evolution.
Lamarck, Darwin and evolution
Jean-Baptiste Lamarck is credited with being the first person to
suggest a coherent explanation of evolution. His idea was that
the environment led to changes in organisms. These changes
could be passed on to their offspring. He gave, as example,
blindness in moles, the presence of teeth in mammals and the
absence of teeth in birds.
Lamarck argued that the long necks of giraffes evolved as
generations of giraffes stretched their necks to reach for ever
higher leaves.
However, this would mean that a characteristic that changed in
a single lifetime was passed on to offspring. We know that this
is not correct.
Lamarck and other scientists of the time based their theories
on speculation (abstract reasoning) rather than evidence.
Charles Darwin had a different idea. The thought evolution
happened by natural selection. Organisms adapt to their
environment by passing the most helpful characteristics on to
their offspring. In this way, the individuals best adapted would
survive. Those not well adapted would perish. Some people
have summarised Darwin’s ideas as ‘survival of the fittest’.
Darwin drew upon his extensive observation of wildlife in
different environments. The Galápagos Islands are a group of
islands on the equator and a very long way from the mainland.
Darwin observed finches living on the islands. He noticed that
although they were basically similar, the size of their beaks
varied from island to island. Source of food differ from island
to island. His explanation was that the finches had beaks that
made it easier to get food from the island they were living on.
So the beaks of all finches on one of the islands were similar,
but different to the beaks of finches living on other islands
© 4science 2013
Jean-Baptiste Lamarck, 17441829, was a French naturalist
Darwin was a young man of 22
when went to the Galápagos
Islands in 1835. He died in 1882.
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