IB Biology Review
Natural Selection, Evolution
& Taxonomy
Vocabulary
Homologous structures
The arms, forelegs, and flippers of different mammals represent
variations on a basic structural theme that have changed
through natural selection to adapt to specific environments
Vestigial Structures
Certain anatomical structures no longer have a use, but
presumably, they had a use in the distant ancestor of the
species;
ex: blind cave salamanders, and the vestigial “legs” of whales
Mimicry
occurs when a group of organisms, the mimics, have evolved to
share common perceived characteristics with another group, the
models
(i.e. a nonpoisonous organism copying the markings of a poisonous
one)
Definitions
Natural Selection
Greater survival and reproductive success of
individuals with favorable heritable variations can
lead to change in the characteristics of a population
Evolution
Evolution is the cumulative change in the
heritable characteristics of a population
Darwin’s Theory of
Natural Selection
What causes natural
selection to occur?
Mutations in DNA caused by
replication mutations
over- or under-expression of genes
environmental factors
Differences allow one individual to have an
advantage over another
Stabilizing Selection Curves
How does natural selection
lead to evolution?
 Variation within the species is necessary (caused by genetic mutations and
meiosis)
 This variation is important because there have to be differences (sometimes
undetectable or at the cellular level) which give one member of a species a
slight advantage over its fellow species member
 There also must be overproduction (overpopulation) and a struggle for
existence
 This is important because the variation between individuals would be
unimportant and would not lead to individual “advantages” if there were
enough “resources” to go around. Ie. There have to be “winners and
losers” in evolution.
 Some members (the “winners” of the species) with the desirable trait(s)
survive and reproduce at a higher rate.
 Over years and years, the phenotypic traits (and their underlying genes) that
led to their success will become more common in the “gene pool
Two Theories of Evolution
Punctuated Equilibrium
evolution occurs in relation to environmental
changes; new traits are put to the test when the
environment changes abruptly
Gradual Evolution
evolution that occurs slowly over time, with
organisms evolving towards a “natural
perfection”
Evidence of Evolution
Fossil Records
The fossil record indicates that living organisms have
progressed from simple to more complex over time
Selective Breeding of Domesticated Animals
through artificial “selection,” people have been changing
species such as pigs, cows, dogs etc. to suit our needs and
desires for millennia
Homologous Structures
represent variations on a basic structural theme that have
changed through natural selection to adapt to specific
environments
i.e. common cilia structure in paramecium and human
windpipes
Taxonomic Classification
What is the order of the categories?
Kingdom
Phylum
Class
Order
Family
Genus
Species
Taxonomic Classification
What pneumonic can be used to
remember the order?
Kingdom
King
Phylum
Phillip
Class
Can
Order
Operate
Family
For
Genus
Good
Species
Spines
Multiple Choice-1
Classification in biology involves putting
organisms that share characteristics together in
groups. In which type of group do the
organisms share the most characteristics?
A.
B.
C.
D.
Class
Family
Genus
Order
Correct answer: C
Multiple Choice-2
What statement can be made about members of
the same order?
A. They all belong to the same genus.
B. They all belong to the same class.
C. They all belong to the same family.
D They can all interbreed successfully.
Correct answer: B
Which names are usually
used to identify an organism?
Genus, species
Example: humans
Genus: homo
Species: sapiens
Multiple Choice-3
The scientific names of two organisms are shown below.
Quercus alba
Angelica alba
What is the relationship between these organisms?
A.
They both belong to the same genus but they are
different species
B.
They both belong to the same species but different
genera
C.
They are both different species and different genera
D.
They both belong to the same species and the same
genus
Correct answer: C
Multiple Choice-4
Which statement most accurately describes the
plants Clarkia cylindrica, Clarkia deflexa, and
Clarkia similis?
A. All three belong to the same species.
B.
C.
D.
Each belongs to a different group.
All three belong to the same family.
Each belongs to a different family.
5 Basic Kingdoms
of Living Things
Basic information about all five kingdoms
At the kingdom level, these above characteristics are used to separate living groups, but
at lower taxonomic levels (phyla, class, order, family, genus) some of the
characteristics used to separate groups are:
•Morphology
What they look like
•Reproduction How they reproduce
•Energy/Food
How they obtain or process it
•Genetic similarities/differences****
How Classification Works
What are the three usual characteristics used?
Morphology
What they look like
Reproduction How they reproduce
Energy/Food How they obtain or process it
What is the best method?
Genetics
This is the most reliable method
What IB Wants
You will need to be able to:
List seven levels in the hierarchy of taxa—kingdom,
phylum, class, order, family, genus and species—using
an example from two different kingdoms for each level.
Distinguish between the following phyla of plants,
using simple external recognition features: bryophyta,
filicinophyta, coniferophyta and angiospermophyta.
Distinguish between the following phyla of animals,
using simple external recognition features: porifera,
cnidaria, platyhelminthes, annelida, mollusca and
arthropoda.
Apply and design a key for a group of up to eight
organisms.
IB Exam Question
1. Explain evolution of a species by natural
selection in response to environmental change.
(7 marks)
species show variation;
variation is inherited;
species have the potential to produce more offspring
than can survive;
this leads to a struggle for existence / survival;
resources are limited;
those that are best adapted (on average) survive to
reproduce;
this leads to a population adapted to the environment;
as the environment changes those that are best
adapted will leave more offspring;
this will cause the species to evolve to a new
adaptation / change in gene frequencies;
IB Exam Question
2. Explain two examples of evolution in response
to environmental change; one must be antibiotic
resistance in bacteria
(8-10 marks)
The Galapagos Islands are near each other, but each has a
unique environment (this is the environmental
change/difference)
A common ancestor of all current Galapagos finches came from
the S. American mainland (these islands are off the coast of S.
America)
The food available on the islands was: seeds (various sizes),
flowers, insects, and plant buds.
There was/is a struggle for existence among the finches (for
food ). Only those finches with beaks adapted to the available
food survive and reproduce – thereby transmitting their genes
to the next generation.
Each finch species adapted over thousands of years to certain
niches in their food gathering capabilities. Their beak shape
was very important and therefore changed to suit the food
source.
IB Exam Question
2. Explain two examples of evolution in response
to environmental change; one must be antibiotic
resistance in bacteria cont.
(8-10 marks)
environmental changes (e.g. application of antibiotics);
affects some individuals more than others;
individuals with antibiotic resistance mutation
survive;
to reach reproductive age / breed to pass on alleles;
result is resistance is best adapted allele / become
more frequent in population;
this is referred to as natural selection;
results in change in species with time / change in allele
frequency;
this is termed evolution;
discussion of punctuated equilibrium / gradualism;