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Biology – Unit 2: Section 4 – Variation, Evolution and
Classification
Variation
Discontinuous and continuous data
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Continuous data is there is no distinct categories and often more of a range within the data
o E
...
height, mass and skin colour
Discontinuous data is where there is two or more set categories and an individual falls in to a set one
o E
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sex and blood group

Variation in phenotype is influenced by variations in genotype
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Individuals within a species have a different genotype (combination of alleles)
Some characteristics are controlled by one gene and are called monogenic these usually show a
discontinuous variation
Whereas others are controlled by a number of genes at different loci making them polygenic these
usually show continuous variation
Different alleles for the same gene are in the same position on the chromosome (this is there loci)

Variation in phenotype is also influenced by the environment
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Most characteristics are controlled by both the genotype and the environment e
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weight
Height
o Is polygenic e
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tall parents usually have tall children
o Affected by environmental factors e
...
nutrition
Monoamine Oxidase A (MAOA)
o An enzyme that breaks down monoamine
o Low levels of MAOA has been linked to mental health problems
o Controlled by a single gene – monogenic
o Environmental factors such as taking anti-depressants and smoking has also been related to
low amounts being produced
Cancer
o Uncontrolled division of cells leading to lumps of cells (tumours) forming
o Risk of cancer can be affected by genes
o Can also be affected by factors such as diet
Animal hair colour
o Polygenic but environment takes part also
o E
...
some artic animals have dark fur in summer but white fur in winter – this is because
environmental changes such as the temperature has triggered the change but the change
wouldn’t have occurred if the animal didn’t have the genes for it

Practise questions
1
...


What is meant by the term locus?
The position on different alleles which codes for a certain gene
What is meant by the term polygenic
Where a number of different genes at different loci code for one phenotype/characteristic

3
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The results showed that women who smoked
during the entire pregnancy had babies with a mean reduction in birth mass of 377 grams
...
What can be concluded
about the influence of genetic and environmental factors on birth mass?
Evidence shows that both smoking and the genotype of the mother had an effect on the birth mass of
new-born babies, however the mother’s genotype had a bigger reduction in birth mass than smoking
...


Adaptation and evolution
Niche
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A niche is the role a species plays within its habitat
o Interaction with other organisms – the food chain
o Interaction with non-living environment – oxygen breathed in and carbon dioxide breathed
out
Every species has its own unique niche however some may be similar e
...
getting eaten by the same
animal but differences in what they eat
If they have the same niche they will be in competition and only one will win
Species are adapted for their niche

Three different adaptations
1
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3
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2
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4
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Useful adaptations become more common because of evolution through natural selection
Individuals within a population show variation within their phenotypes
Predation, disease and competition create a struggle for survival
Those with better adaptations e
...
running faster, are more likely to survive and therefore reproduce
and pass on their advantages to offspring
Number of individuals with the advantage increases
Favourable adaptation becomes more common and therefore evolution
Peppered moths
o Show variation in colour e
...
light ones and dark ones
o Before 1800’s more light coloured moths
o During the 1800’s tress were darkened through pollution, these were what the moths lived
on
o Darks moths were not better adapted as they were camouflaged so more likely to survive
and reproduced, passing on their genes
o Number of dark moths increased

Practice questions
1
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3
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How many species can occupy a single niche
One
What is meant by the term adaptation?
It is a behaviour, physiological or anatomical advantage that makes the species more likely to survive
and reproduce
Describe the difference between behavioural, physiological and anatomical adaptations
A behaviour adaptation is how the organism acts to increase its chances of survival, a physiological
adaptation is a process inside the organisms body that increases their chances of survival and a
anatomical adaptation is a structural feature that aids survival
Describe what is meant by the term niche
A niche is a species role within its habitat, this can include how is interacts with other organisms such
as its place in the food chain or how it interacts with non-living things in the environment such as
breathing

5
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Hedgehogs are commonly found in gardens across the UK
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They hibernate over winter and can roll into a ball when alarmed
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A behavioural adaptation is them rolling into a ball when alarmed, this means that they are protected
by their spiky fur, a physiological adaptation is hibernating over winter, this could be because there is
little food around for them in winter so they need to reserve energy
...

Explain how natural selection can lead to adaptations becoming more common in a population
there will be variations within a species, some of these variations will be more beneficial than others
which increases their chances of survival meaning they are more likely to reproduce and pass on their
beneficial adaption to offspring
...


Classification
Grouping together of similar organisms
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Taxonomy is the science of classification
Severn levels of groups (taxonomic groups) used in classification
Similar organisms are placed into a large groups called kingdoms
Similar organisms that are within the kingdom are organised into phylum which are
then organised into class etc
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2
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4
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Prokaryote/Monera e
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bacteria
Prokaryotes, unicellular, no nucleus, less than 5 µm
Protoctista e
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algae and protozoa
Eukaryotic cells, usually live in water, single-celled or simple organisms
Fungi e
...
moulds, yeasts and mushrooms
Eukaryotic, chitin cell wall, saprotrophic (absorbs substances from dead or decaying organisms)
Plantae e
...
mosses, ferns and flowering plants
Eukaryotic, multicellular, cell walls made of cellulose, can photosynthesise, contain chlorophyll,
autotrophic (produce their own food)
Animalia e
...
nematodes (roundworms), molluscs, insects, fish, reptiles, birds and mammals
Eukaryotic, multicellular, no cell wall, heterotrophic (consume plants and animals)

Three Domains vs Five Kingdoms
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The three domain classification system was proposed on new data which came available through
molecular phylogeny
o Study of the evolutionary history of groups of organisms
o Says which species are related and how closely they are related
o Looks at DNA and proteins to see how closely related they organisms are
The three domains is a large superkingdoms that are above the kingdoms in the taxonomic hierarchy
Prokaryote kingdom is separated into two out of the three domains – archaea and bacteria – they and
unicellular and have no nucleus
The other four kingdoms - protoctista, fungi, plantae, animalia – are placed under the Eukarya domain
– these are organisms with cells that contain a nucleus
Prokaryote were reclassified into two domains because molecular phylogeny suggested that archaea
and bacteria are more distantly related than originally thought

Practise questions
1
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3
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a
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Phylum
Chordata
Chordata

Class
Mammalia
Mammalia

Order
Primates
Primates

Family
Hominidae
Hominidae

Genus
Homo
Pan

Name four features the bonobo must have to place it in the kingdom Animalia
Eukaryotic cells, multicellular, no cell walls and heterotrophic

Species
Sapiens
Paniscus



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