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Markschemes for Topic 5
5.1
Outline the
evidence for
evolution
provided by
homologous
structures.
(6)
comparative anatomy of groups of animals or plants shows certain
structural features are basically similar;
homologous structures are those that are similar in shape in different
types of organisms;
structural similarities imply a common ancestry;
(homologous structures) used in different ways;
example is pentadactyl limb in vertebrates / modification of ovary
wall or pericarp to aid seed dispersal / other suitable example;
adapted to different mode of locomotion in particular environment /
example of two differences such as bat’s wing and human hand;
illustrates adaptive radiation since basic plan adapted to different
niches;
the more exclusive the shared homologies the closer two organisms are
related;
certain homologous structures in some species with no apparent function
such as human appendix (homologous with functional appendix in
herbivores); 6 max
Outline five types
of evidence
which support the
theory of
evolution by
natural
selection. 6 marks
Describe what
happens in gene
pools when
evolution occurs
and why.
Explain why the
following
examples are
evidence of
evolution.
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geographic distribution
ring species/other evidence from geographical distribution
biochemistry
cytochrome c/other biochemical evidence
fossils/paleontological
fossilized horse ancestors/other evidence
homologous structures
pentadactyl limb/vertebrate embryos/other
recent observed evolution
resistance to antibiotics/insecticides/heavy metal tolerance/other recent
example
Gene pools are relatively stable over time, however, when changes occur,
evolution is seen
• New combinations of alleles lead to new phenotypes, that can then be
selected for or against by the environment
• Alleles that are advantageous to a populations survival will be passed
on and have a higher frequency in later generations
• Alleles that are disadvantageous will not be passes on and have a lower
frequency in later generations
• Immigrations and emigrations will also have an effect on allele
frequencies
• For whatever reason, when a gene pool in modified, some degree of
evolution has occurred.
•
Fossil Record
• indicates that life on earth is constantly changing and these changes
occur over long periods of time (hundreds of thousands or millions of
years)
• Fossil - preserved remains of ancient organism.
•
Support the idea that life existed on earth over 500 million years ago
Artificial Selection
 changes over time in domesticated animals or plants that are chosen
by breeders
Homologous Structures
• Homologous structures: Structures that are similar in form but may have
different functions, found in different species
• Indicates a common ancestor
•
Vestigial Structures
• Vestigial organs
• Organs of many animals are so reduced in size that they are just
vestiges, or traces, of homologous organs in other species
• These do not affect an organism’s ability to survive and
reproduce
Embryonic Similarities:
• Early stages, or embryos, of animals with a backbone are very similar
• Same groups of embryonic cells develop in the same order and pattern
to produce the tissues and organs of all vertebrates
5.2
Outline how
antibiotic
resistance in
bacteria can
arise in
response to
environmental
change. 5
marks
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Briefly explain
Darwin`s theory of
evolution. 4 marks
Outline one
modern example
of observed
evolution by
natural
selection. 2 marks
antibiotic resistance can be inherited;
alleles for resistance can be passed from one cell to another by
exchange of
plasmids/conjugation;
some varieties are more resistant than others;
bacteria reproduce very rapidly and have high mutation rate;
evolution can occur rapidly;
increased exposure to antibiotics is the environmental change that
selects for resistant varieties;
for example, in hospitals / animal feed / inappropriate prescriptions /
not finishing prescriptions;
bacteria without resistance die / resistant bacteria survive and pass on
genes to next generation;
results in change in genetic makeup of population;
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parents produce more offspring than survive
there is competition among members of a species for survival/struggle
for existence
species show variation
certain variations will give a selective advantage/survival of fittest
depending on environment
these variations will be passed on to the next generation
leading to change in allele frequency
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named example
selective pressure
result
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Outline the
process of
evolution with
regards to natural
selection
What causes
variety in the
offspring of
populations?
Begins when an overproduction of offspring occurs in a population (group
of interbreeding individuals that live in the same place and time)
• Most organisms produce far more offspring than could survive in an
environment
• Creates competition for resources (food, water, spaced, etc.) in
populations which leads to the struggle for survival
• Competition leads to adaptive behaviors/characteristics to gain/use
more resources.
• Adaptations can lead to variation within species and populations
• Variations can provide individuals with advantage or disadvantage for
survival (natural selection)
• These advantages can lead to some individuals likelihood to survive and
reproduce, which may ultimately lead to the formation of a new
species
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What is meant by
the survival of the
fittest?
Mutations in DNA can lead to harmful or beneficial changes in organisms
phenotype
• In Each generation only a few genes mutate and most have little
affect on phenotype
Sexual reproduction is more powerful source of variation through meiosis
and fertilization
• Meiosis: Random distribution of chromosomes results in each egg and
sperm having different combinations from others
• Fertilization: Combination of different genes from sperm and egg cell
and only one sperm cell can fertilize one egg cell. Leads to variation
in offspring
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Outline the
process of natural
selection
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5.3
5.4
Create a
Cladogram for
the following
organisms and
features:
Individuals with characteristics that are not well suited to their
environment – those with low levels of fitness – either die or leave few
offspring
Individuals that are better suited to their environment – adaptations that
enable fitness – survive and reproduce most successfully
Individuals w/in population overproduce offspring, which have natural
variation due to genetic differences
Individuals with poorly adapted characteristics are less successful at
gathering resources and have lower chance of survival
Individuals with well adapted characteristics are more successful at
gathering resources and have a higher chance of survival
Individuals that survive have a better chance at reproducing and
passing on their genetic traits
Over many generations the accumulations of genetic characteristics in
a population results in evolution
Features: Vertebrate, Bony Skeleton, Four limbs, Amniotic Egg, Eggs w/shell,
Feathers, Hair, Opposable Thumbs.
Organisms: Shark,
Fish, Frogs,
Crocodiles, Birds,
Rodents,
Primates.
Features:
Vertebrate, Bony
Skeleton, Four
limbs, Amniotic
Egg, Eggs w/shell,
Feathers, Hair,
Opposable
Thumbs.