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Summary IB Biology Topic 5: Evolution and Biodiversity
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  • Biology SL and HL
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  • International Baccalaureate Diploma
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Detailed objective-by-objective summary notes for Topic 5: Evolution and Biodiversity for IB Biology SL/HL. Contains information on everything you need to know from 5.1 to 5.4, according to each understanding, application or skill. Written by a IB HL Biology student who graduated with a 45/45.

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  • March 5, 2019
  • 5
  • 2016/2017
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  • biology
  • ib biology
  • topic 5
  • evolution
  • biodiversity
  • international baccalaureate
  • ib
  • hl
  • sl

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  • International Baccalaureate Diploma
  • Biology SL and HL
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IB TOPIC 5 | EVOLUTION AND BIODIVERSITY
2016 | SYJ0014


Topic 5.1: Evolution and biodiversity – Evidence for evolution
There is overwhelming evidence for the evolution of life on Earth.

• Understanding: Evolution occurs when heritable characteristics of a species change.

 Evolution: cumulative change in the heritable characteristics of a population through natural selection
 Implication of evolution: implies that all living organism share a common ancestor

• Understanding: The fossil record provides evidence for evolution.

 Fossil records as an evidence for evolution:
 Succession in fossils: fossils in aged strata showed that fossils of most primitive forms of life are the oldest
 Ecological sequence: the sequence in which they appear matches the sequence they are expected to evolve

 Example: horses; fossil record is extensive; shows that horse became progressively specialized for running

• Understanding: Selective breeding of domesticated animals shows that artificial selection can cause evolution.

 Selective breeding: artificial mechanism of evolution that occurs when individuals with desirable phenotypes are bred
 Mechanism: selected phenotypes become more common as unfavourable ones get removed from breeding pool
 Purpose: the population continuously show traits favourable to humans

 Example: dogs (better at hunting, detection etc.), cows (more milk), sheep (more wool)

• Understanding: Evolution of homologous structures by adaptive radiation explains similarities in structure when there are differences in
function.

 Homologous structures: structures that show a similarity in characteristic derived from a common ancestor
 Analogous structures: structures with the same function but derived from a different ancestry
 Adaptive radiation: type of divergence where one species diverges into different species

 Example of divergent evolution:
 Darwin’s finches: finches diverged into different populations specialized in different niches so they cannot interbreed
 Pentadactyl limb: limbs in different species have different function yet with the same base anatomy
 Comparative embryology: the early embryonic stages of all vertebrates are very similar

• Understanding: Populations of a species can gradually diverge into separate species by evolution.

 Speciation: process in which populations of a species gradually diverge into separate species
 Cause: speciation has occurred when two population merge again and does not interbreed anymore
 Isolation lead to evolution in different direction through natural selection

• Understanding: Continuous variation across the geographical range of related populations matches the concept of gradual divergence.

 Gradualism model: speciation that predicts evolution as a long, gradual sequence of intermediate forms
 Causes: characteristic from various genes (many genes of small effect)
 Drivers: many genes of small effect
 Evidence: continuous various across geographical range of related populations (e.g. lava lizards of Galapagos Island)

• Application: Comparison of the pentadactyl limb of mammals, birds, amphibians and reptiles with different methods of locomotion.

Type of organism Example Function of limb
Mammals Human, cat Control of tools, walking, jumping
Birds Penguins, doves Flying, swimming, walking
Amphibians Frog Jumping, walking
Reptiles Lizard Walking

• Application: Development of melanistic insects in polluted areas.

 Industrial melanism: proportional increase of dark, or melanin, pigments in individuals of a population, caused by changes in the
environment resulting from industrial pollution

 Evolution process of Melanistic moths:
 Pre-industrialization: light moths are common as the trees are lighter coloured; birds easily find dark ones
 Industrialization: trees blacken, and dark moths increase in frequency as birds easily find light ones on black trees
 After emission control legislation: level of pollution declined, population of dark moth sharply decline again

• Nature of science: Looking for patterns, trends and discrepancies—there are common features in the bone structure of vertebrate limbs
despite their varied use.




LAST EDITED 2017-03-15 | 1

, IB TOPIC 5 | EVOLUTION AND BIODIVERSITY
2016 | SYJ0014


Topic 5.2: Evolution and biodiversity – Natural selection
The diversity of life has evolved and continues to evolve by natural selection.

• Understanding: Natural selection can only occur if there is variation among members of the same species.

 Individuals in species share the same genes but with different versions resulting in variation
 Natural selection depends on such variations; individuals with more favourable traits tend to survive

• Understanding: Mutation, meiosis and sexual reproduction cause variation between individuals in a species.

 Cause of variation between individuals in a species:
 Mutation: original source of new alleles that enlarges the gene pool
 Meiosis: produces new combinations of alleles through crossing over and independent orientation
 Sexual reproduction: allows mutations that occurred in different individuals to be brought together

• Understanding: Adaptations are characteristics that make an individual suited to its environment and way of life.

 Adaptation: inherited characteristics evolved through natural selection that makes an individual suited to its environment
 Non-directional nature of adaptation: adaptation through natural selection does not develop with a direct purpose

• Understanding: Species tend to produce more offspring than the environment can support.

 Overpopulation: production of offspring than the environment can support; general trend in most species

• Understanding: Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or
produce fewer offspring.

 Darwin and Wallace’s theory of evolution: “Theory of Natural selection”
 Variation: chance variations between individuals occur within species
 Heritability: organisms beget like organisms, and so some of the variation among individuals is passed down
 Overpopulation: more offspring are produced each generation than can be supported by the habitat
 Selective pressure: some individuals with certain traits have a higher chance of surviving and reproducing (competition)

• Understanding: Individuals that reproduce pass on characteristics to their offspring.

 Inherited characteristics: characteristics an individual is born with; passed on to offspring
 Acquired characteristics: characteristics acquired during the lifetime of an individual; not passed on to offspring

• Understanding: Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the
frequency of other characteristics leading to changes within the species.

 Gene pool: combination of all genes in a population and frequency of alleles for each gene
 The favourable alleles increase in frequency in the gene pool due to natural selection
 Ratio of alleles and genotype will gradually change (evolve) with time

• Application: Changes in beaks of finches on Daphne Major.

 On Daphne Major island, species of bird (Geospiza fortis) feed on large and small seeds
 Their beak length correlated with their size and availability of diet over years

 Event of natural selection:
 1977 – drought caused shortage of small seeds; highest mortality amount short beaked individuals
 1982-1983 – increased supply of small seeds; increased population among short beaked individuals
 1987 – weather back to normal, less small seeds; decreased population among short beaked individuals

• Application: Evolution of antibiotic resistance in bacteria.

 Process of antibiotic resistance development in bacteria:
 Exposure to antibiotic: population is exposed to antibiotics
 Mutation of bacteria: in a population with no resistance, a bacterium with antibiotic resistance form with mutation
 Natural selection: survival becomes more advantageous for bacteria with resistance, so this strain becomes prevalent in
 Resistance propagation: most individuals in the population becomes antibiotic resistant with transformation

 Reason for prevalence of antibiotic resistance:
 Hospital use: uncontrolled use in hospital that allows for resistance development
 Livestock feed: antibiotic use in animals to increase yield
 High chance of mutation in bacteria: high chance for bacteria to mutate and survive
 Transformation ability of bacteria: ability of bacteria to pass genes onto other bacteria through plasmids

• Nature of science: Use theories to explain natural phenomena—the theory of evolution by natural selection can explain the development of
antibiotic resistance in bacteria.

• Guidance: Students should be clear that characteristics acquired during the lifetime of an individual are not heritable.
• Guidance: The term Lamarckism is not required.




LAST EDITED 2017-03-15 | 2

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