Download Natural Selection

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3.30 Describe the process of evolution by
means of natural selection.
3.32 Understand how resistance to antibiotics
can increase in bacterial populations (natural
selection).
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Darwin put forward the theory of
‘natural selection’.
It can be summarised by the
following points:
Variation
Over-production
Struggle for existence
Survival of the fittest
Advantageous characteristics passed
on to offspring
◦ Gradual change
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Variation
 Organisms are genetically different, they have
different characteristics
 Some may be slightly better adapted to their
environment than others.
Over-Production
 More offspring are produced than will
survive.
Struggle for Existence
 There will be competition between organisms
for resources e.g. food, water, light, shelter
and mates.
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Survival of the Fittest
 Only those who are best adapted to their
environment will survive and reproduce (the
strongest).
Reproduce
 Beneficial genes and characteristics will be
past onto offspring when these organisms
reproduce
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This is the theory of natural selection - when
nature selects which organisms will survive
and reproduce. Those that are best-adapted
to their environment will pass their genes
onto their offspring.
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Some bacteria can become resistant to
antibiotics, such as penicillin.