Student Notes
Williamwood High School
National 5 Biology
Unit 3 – Life On Earth
Section 3.1 Biodiversity and the Distribution of Life
Section 3.2 Energy in the Ecosystem
Section 3.3 Sampling Techniques
Section 3.4 Adaptation, Natural Selection and Speciation
Section 3.5 Human Impact
Student Notes___________________
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Student Notes
Learning Outcomes:

A mutation is a random change to genetic material. Mutations may be neutral, confer an
advantage or disadvantage. Mutations are spontaneous and are the only source of new
alleles. Environmental factors, such as radiation and chemicals, can increase the rate of
mutations.

Variation within a population makes it possible for a population to evolve over time in
response to changing environmental conditions.

Natural selection/survival of the fittest occurs when more offspring are
produced that the environment can sustain. Only the best adapted
individuals survive to reproduce, passing on genes that confer the selective
advantage.

Speciation occurs after a population becomes isolated and natural
selection follows a different path due to different conditions/selection
pressures.
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Student Notes
Mutations
Mutations are random changes to an organism’s genetic material. Mutations are spontaneous
and random but can be caused by exposure to mutagenic agents such as radiation, UV light or
toxic gases such as mustard gas.
Mutations to sex cells can lead to inherited conditions in offspring. Mutations in body cells can
lead to cancer. Mutations can be detrimental to an organism but could also be of benefit. Serious
mutations can be caused by an alteration of a single base on a length of DNA that results in a
change to the protein produced. Changes to chromosomes may occur when pairing up during
gamete formation or during cell division when spindle fibres fail.
Advantageous Mutations: Very rarely the changes may even be beneficial to us and produce
new and useful characteristics e.g. polyploidy in plants gives increased yield.
Neutral Mutation: Sometimes the changes are small and the organism survives with no obvious
difference e.g. an extra toe.
Disadvantageous Mutation: Sometimes these changes can be so severe that the organism dies or
have serious disorders e.g. metabolic disorders and cystic fibrosis.
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Student Notes
Variation
All members of a population show variation, these are differences caused by subtle differences in
genetic information. Variation involves small changes between organisms which may allow that
organism to compete better for survival.
Organisms that survive to reproduce pass on their genetic information to the next generation.
Over time organisms evolve in response to environmental condition.
Adaptations
Organisms are adapted to survive in different conditions.
Adaptations are inherited characteristics that make an organism well suited to survive in it’s
niche. Well adapted organisms are better at:

competing for food,

escaping from predators or

fending off disease.
Special adaptations are required to survive in extreme habitats.
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Student Notes
Adaptations – The Desert
Deserts are hot and dry during the day, but cold at night. Deserts have very little rain and very
little shade.
Camels, desert rats and cacti are well adapted for survival in the desert.
Camels have:

Large, flat feet to spread their weight on the sand.

Thick fur on the top of the body for shade, and thin fur
elsewhere to allow easy heat loss.

A large surface area to volume ratio to maximise heat
loss.

The ability to go for a long time without water.

The ability to tolerate body temperatures up to 42°C.

Slit-like nostrils and two rows of eyelashes to help keep the sand out.
The desert rat shows both behavioural and physiological adaptations to living in the desert.
Behavioural adaptations to reduce water loss:
 Remains in burrow during the day where it is cooler
and more humid.

Forages for food at night when it is cool.
Physiological adaptations to reduce water loss:
 Does not sweat.
 Has dry nasal passages.
 Produces dry faeces and concentrated urine.
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Student Notes
Cacti are well adapted for survival in the desert.
Cacti have:
 Stems that can store water.
 Widespread root systems that can collect water from a
large area.
 Cacti have spines instead of leaves. These minimise the
surface area and so reduce water loss by transpiration.
The spines also protect the cacti from animals that might
eat them.
Adaptations – Arctic Tundra
Conditions in the arctic are cold, reaching -50°C in the winter and under 10°C in the summer.
There is little rain and high winds.
Polar bears are well adapted for survival in the Arctic. They have:

A white appearance, as camouflage from prey on the snow and ice.

Thick layers of fat and fur, for insulation against the cold.

A small surface area to volume ratio, to minimise heat loss.

A greasy coat, which sheds water after swimming.
The Bush baby
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Student Notes
Bush babies are found throughout East Africa as well as
in woodlands and bushlands in sub-Saharan Africa. Most
often, they live in tree hollows that provide shelter.
Sometimes, they construct nests in the forks of
branches, or natural holes. Bush babies prefer trees with
little grass around them, probably as a precaution
against wildfires. Bush babies are omnivores. They are
predated by hawks, owls and large snakes. They are
nocturnal.
Changing environmental conditions
An organism’s niche can change due to environmental conditions. Changing conditions can be
due to a natural disaster such as flood, drought or fire. Organisms may be faced with shortages of
food, nutrients, water, shelter or light. Organisms that survive are the one’s that have useful
adaptations to compete effectively for resources. The survivors will pass on their characteristics
to offspring.
Natural Selection
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Student Notes
“Survival of the fittest”
All organisms produce offspring to carry on their species. Selection pressures are different for
individuals of the species, those not adapted may die. The best adapted individuals survive and
pass on their favourable alleles. Over time this leads to evolution; the rise of some species and
the extinction of others. As environments are constantly changing, so are the characteristics of
populations.
Natural Selection occurs when more offspring are produced than the environment can support.
Only the best adapted can survive and pass on the advantageous genes.
Charles Darwin first proposed his theory of evolution by natural
selection in 1858.
The theory of evolution states that evolution happens by natural
selection.
Here are the key points:
1) Individuals in a species show a wide range of variation.
2) This variation is because of differences in genes.
3) Struggle for survival.
4) Individuals with characteristics most suited to the environment in which they live are more
likely to survive and reproduce.
5) The genes that allowed the individuals to be successful are passed to the offspring in the next
generation.
6) Species change over a period of time.
Natural Selection
– Industrial Melanism
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Student Notes
There are some examples where the process of natural selection takes place fast enough to be
observed.
Before industry: most peppered moths were of
the pale variety. This meant that they were
camouflaged against the pale birch trees that
they rest on. Moths with a mutant black
colouring were easily spotted and eaten by birds.
This gave the white variety an advantage, and
they were more likely to survive to reproduce.
After industrial revolution: Pollution blackened
the birch tree bark with soot. The mutant black
moths were now camouflaged, while the white
variety became more vulnerable to predators. This
gave the black variety an advantage, and they
were more likely to survive and reproduce.
The ‘clean air act 1956’ reduced the pollution released by factories. The lichens on trees grew
back, the pale moths were once again camouflaged from predators and the dark moth started to
decline again.
Speciation – A Species
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Student Notes
A species is a group of organisms able to interbreed and produce fertile offspring.
Different dog breeds show great variation, but the individuals still belong to the same species. Dogs,
regardless of breed, can have puppies together this means they are the same species.
Some organisms are closely related and so can breed together, but the offspring are infertile.
Lions and tigers can breed, producing a liger but ligers are infertile, this means lions and tigers are not
the same species.
Speciation – Isolation Barriers
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Student Notes
Speciation is a process that allows a new species to develop. A population of one species can only
evolve into more than one species if groups within the population become isolated from each other
by barriers that prevent exchange of genes.
Geographical: Features such as oceans, rivers or mountains isolate
groups.
Ecological: Isolated by features such as habitat, pH or salinity.
Reproductive: differences in courtship behaviour, physical
differences which prevent mating, or failure of gametes fuse.
Speciation – Stage 1
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Student Notes
Large population with common gene pool.
Speciation – Stage 2
Large population becomes split by an isolating barrier (geographical, ecological or reproductive).
There are different conditions on each side of the barrier.
Speciation – Stage 3
Different mutations occur in each group. The mutations are spontaneous, rare and random.
Mutations create new alleles.
Speciation – Stage 4
If the environments differ they will provide different selection pressures (climate, predation or
diseases). Different adaptations are favoured by natural selection. Beneficial mutations are passed
on to offspring.
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Student Notes
Speciation – Stage 5
If the isolating barrier is removed after a long period of time they will no longer be able to
interbreeding to produce fertile offspring as they are now 2 different species.
Give an account of the importance of isolating mechanisms, mutations and natural selection in
the evolution of new species.
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Student Notes
Rapid selection
Bacteria such as MRSA have become resistant to antibiotics. As each bacteria is different within the
population some have natural resistance to antibiotics. As most bacteria are sensitive to antibiotics
the more they are exposed, the greater the resistance to antibiotics becomes. Since bacteria can
reproduce so rapidly, evolution occurs very fast.
The plates show bacteria growing on agar plates with antibiotic discs. Where there is a clear zone the
bacteria have been killed. The bigger the clear zone the more effective the antibiotic. Where there is
no clear zone the bacteria is resistant. With increasing resistance to antibiotics their use must be
limited for the most severe of infections.
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Student Notes
Success Criteria
I can describe what is meant by a mutation and what can increase the
rate of mutation.
I can describe adaptations of plants and mammals to living in the desert.
I can describe what is meant by the term “Natural Selection”.
I can give examples of natural selection in action.
I can explain the process of natural selection.
I can state what a species is.
I can describe the process of “speciation” – the formation of a new
species.
I can describe examples of speciation in action.
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