Module 3: Biological Diversity – Part 1: Effects of the Environment on Organisms

Introduction
 Biological diversity or biodiversity refers to the variety and abundance of different species of
plants and animals
o Biodiversity can be affected slowly or quickly over time by natural selection
pressures
o Human impact can affect biodiversity over a shorter time period
o The general health of the planet depends on biodiversity. In all ecosystems, the
greater the biodiversity the more stable and resilient the system becomes
Organising the ecosystem
Ecosystem: made up of organisms (biotic) living in an area that interact with each other and with the
non-living (abiotic) environment in which they live
Community: groups of different species living in the same habitat and interacting with one another
Population: group of organisms of the same species living together in a defined geographical area
Organism: an individual of a species
3.1.1 predict the effects of selection pressures on organisms in ecosystems, including:
 Biotic factors
 Abiotic factors
Selection pressures
 Selection pressures are changes in the environment that put constraints on organisms and
determine which individuals are best suited to the prevailing conditions
 Abiotic factors or non-living environment (e.g. amount of water, temperature, amount of
light, types of rocks and soil etc.) and how these affect the biotic environment
 Biotic factors or living organisms (plants, animals, microbes etc.) that live in the area and
how these living things interact with each other
Abundance and distribution
Distribution: of a species describes where it is found
Abundance: of a species determines how many individuals of that species live throughout the
ecosystem
 Organisms occupy the areas where the biotic and abiotic factors of the environments suit
them. They live where their chances of survival are high, where their requirements for
survival are met, and where they are able to avoid predators
 Abiotic and biotic selections pressures affect the distribution and abundance of organisms in
an ecosystem by causing fluctuations or changes in population numbers and movement.
Populations may occupy certain areas and not others due to the resources that are available
Abiotic factors
 Abiotic factors are the non-living factors in an environment including:
o Temperature
o Water availability
o Air pressure
 o Gas (O2 and CO2) concentration
o Light intensity
o Salinity

Biotic factors
 Biotic factors are the living factors in an environment including:
o Availability and abundance of food
o Number of competitors
o Number of mates
o Number of predators
o Number and variety of disease-causing organisms

Changes in a population over time

 Within a population individuals are characterised by a variety of inherited traits
 In a changing environment, where there is an abiotic or biotic selection pressure, some of
those traits will provide an advantage
 Individuals with the advantageous traits will survive, breed and pass these traits on to their
offspring so that, over time, these traits will become more common in the population. This is
how the population will change over time
3.1.2 investigate changes in a population of organisms due to selection pressures over time, for
example:
 Cane toads in Australia
Cane toads
 The cane toad is native to South and Central America. It was deliberately introduced into
Australia in 1935 to control the greyback cane beetle in sugar cane plantations
 The cane toad has spread from Queensland into the NT and NSW. The toad ‘frontline’ is
currently travelling up to 60km a year
 From the 102 toads originally released, their population is now estimated at 200 million
 Cane toads are thriving in Australia because:
o They feed mainly at night as there is less competition
o They are ground dwellers
o They eat anything that fits into their mouth: insects, snails, small marsupial mice,
birds and a wide variety of other opportunistic foods such as pet food
o They have no known predators
o They breed all year round. The female can lay up to 30 000 eggs at a time that hatch
in 2-3 days
 Cane toads contain toxins that kill many native animals. Glands on the toad’s shoulders
product bufotoxin which acts on the heart and central nervous system causing a rapid
heartbeat, convulsions and paralysis. A dog can die from drinking water in which a toad has
been swimming
 Although some animal populations have decreased since the arrival of the cane toad, not all
members of a population are affected in the same way because of variation:
o Some individuals are more tolerant to the person
o Some individuals will be more reluctant to try to eat cane toads
 Cane toads are considered to be a selection pressure because:
o Those predators with characteristics such as vulnerability to bufotoxin and increased
preference to eat toads die and are removed from the population (selected against)
 o Predators that have increased resistance for the bufotoxin and those that are reluctant
to eat cane toads survive and reproduce (selected for)
 Therefore, populations of Australian animals are changing in response to the cane toad
Cane toads and red-bellied snakes
 Since the introduction of the cane toad, the head size of a red-bellied black snakes has gotten
smaller. Why?
o Snakes with larger heads ate larger toads which produce more toxin and they died
o Smaller headed snakes were unable to open their jaws wide enough to eat larger toads
and therefore survived and reproduced
 Therefore the cane toad is a selection pressure acting on snake head size
Cane toads and quolls
 Northern quolls suffered drastic population reduction when the cane toad arrived
 For unknown reasons, quoll populations in Queensland have stopped eating cane toads
 Scientists suspect that there is a gene that makes the quolls ‘toad adverse’
 Quolls with this gene avoid the toads, and have survived and reproduced to pass on the gene
 Therefore, the cane toad is a selection pressure acting on quolls in Queensland to change
their diet
Changes in cane toad characteristics
 Cane toads are also changing in a process called spatial sorting
 The toads with the fastest hopping style (straight hoppers) have accelerated the invasion front
from 15km per year to 60km per year
 The fast toads at the front have offspring who themselves are fast
 However, this has lead to increased pressure on the toad’s spines and a 10% increase in spinal
arthritis. Faster cane toads may also have vulnerable immune systems because of the stress on
their bodies
Cane toad control
 Cane toad tadpole pheromones can slow the development of eggs, so a synthetic pheromone
is being developed to stop the development of eggs
 Large and aggressive meat ants will attack and eat small toads and could be used as a
biological control for the small toads
 Toad busters is a group of environmental ‘vigilantes” responsible for catching toads in the NT
and humanely killing them by gassing them with CO2 and then freezing them
‘toads day out’ event in QLD catches toads and turns them into wallets and gold gloves marketed in
japan
 Prickly pear distribution in Australia
Prickly pears in Australia
 The prickly pear was initially introduced into Australia from the Americas in the 1800s as a
food plant for the cochineal beetle (which was used to make red dye)
 At the time Spain had a monopoly of the expensive red dye, which was used in the clothing
industry. Prickly pear could also be used as a strong hedge plant and an alternative source of
food for stock
 The plant reproduced quickly by branching and growing many new plants very quickly
  Due to the lack of selection pressures, by 1925 the prickly pear had become a weed, making
50% of 24 million acres of Qld and Northern NSW unavailable to farmers because the cactus
was so dense
Controlling the prickly pear
 In 1925, the Prickly pear Travelling commission introduced the small cactoblastis moth to
Australia.
 The caterpillars of this moth ate away the leaves of the prickly pear and become a significant
selection pressure. By 1933 only 10% of the cactus survived, reducing the distribution of the
prickly pear
 To this day, the cactus and moth are in ecological balance in Qld so that the cactus is no
longer a pest, and the moth has been used in other countries to control the cactus
 This was an international success story of biological control
Part 2: Adaptations
Adaptations
 An adaptation is a characteristic that an organism has inherited and that makes it suited to its
environment. An organism does not intentionally change to suit its environment, nor can it
intentionally produce offspring that have these changes
 An adaptation is a result of a change or variation that arises, at random, when cells divide and
replicate during reproduction. The offspring produced possess a changed feature and this
random difference may happen to benefit the organism by making them more suited to their
environment
 There are three types of adaptations
1. Structural – how an organism is built
2. Physiological – how an organism functions
3. Behavioural – how an organism acts or behaves
3.2.1 conduct practical investigations, individually or in teams, or use secondary sources to examine
the adaptations of organisms that increase their ability to survive in their environment, including:
 Structural adaptations
Structural adaptations
Structural adaptations are physical characteristics, found both inside and outside the organism, to
improve an organism’s ability to cope with abiotic and biotic factors in their environment
The main survival issues for animals are:
 Gaining enough food and water
 Keeping cool or warm
 Finding space to live
 Reproducing
 Deterring predators (e.g. spines for protection)
Keeping cool and warm
Animals in hot, dry climates:
 Are often small, with a large SA:V ratio, so that the animal can cool down and heat up
quickly
  Have large ears, long tails or a long body which are highly vascular (many blood capillaries)
so that the animal can lose heat
Animals in cold climates:
 Are often larger, with a small SA:V ratio, so that the animal can conserve heat
 Have small ears and other extremities to reduce heat loss
 Thick fur and blubber (fat) to insulate against cold
Structural Adaptations of Australian Animals
 Koala have adaptations that allow them to exist in an arboreal habitat (trees):
o Strong claws and muscular legs that enable them to move quickly up the trees in a
jumping motion
o Their hands are arranged so that two fingers oppose the other three, this makes it easy
to grip branches
o Koalas do not produce the enzyme cellulase that breaks down cellulose in plants, so
they have a huge caecum (bag of microorganisms) in their gut
Structural Adaptations of Plants
 Water is essential for photosynthesis. Many structures in plants are adaptations to reduce
water loss from heat, wind and salinity:
o Reduced leaf surface area
o Thick, waxy cuticle
o Rolled leaves
o Leaves oriented away from sunlight
o Leaf abscission (shedding)
o Sunken stomates
o Stomatal hairs that create a humid microclimate – less transpiration

Hot and Cold Environments

Hot, dry environments:
 Plants that grow in hot, dry environments are known as xerophytes. They have adaptations to
conserve moisture and prevent the leaf temperature from rising too much. They have
increased tolerance for desiccation (or drying)
 Examples:
o Sclerophylls (hard-leaved plants) like eucalyptus, wattles and banksia
o Succulents (fleshy-leaved plants) like cacti (prickly pear)

Cold, dry environments:

 In very cold environments, water freezes and becomes inaccessible to plants
 Cold environments also become dry environments, so plants develop similar adaptations
o Reduce surface area into needles
o Shed leaves (deciduous)
o Thick waxy cuticles

Structural Adaptations of Australian Plants

 Banksia -the medium sized tree has adaptations that enable it to live in water-poor sandy
soils:
o Masses of fibrous roots absorb minerals and water
 o Dense foliage with small, tough, spiky leaves prevent water loss
o Thick cuticle on each leaf and the slightly curled-over leaf edge prevent water loss
o The bark is very rough, thick and heat resistant to allow the tree to survive a bushfire.
The large woody fruit dry out and crack open to reveal winged seeds that germinate
easily in ash
 Physiological adaptations
Physiological Adaptations
 Physiological adaptations help regulate functioning within an organism. They usually have
to do with the functioning of biochemical reactions within cells and tissues of an animal
 For example: endotherms often speed up their metabolism to create enough heat to maintain
their body temperature
Physiological Adaptation: heat exchange
 Penguins can live in very cold environments like the Antarctic
 Penguins keep their feet warm using a counter-current heat exchanger. Blood travelling in
the arteries to the foot warms the blood returning to the body from the foot in the veins
 Because the gradient of temperature difference between the foot and surroundings is reduced,
less heat is lost from the penguin’s body
Physiological Adaptations of Plants
 Plants can also adjust functioning in cells or tissues
 For example: to live in dry environments, some plants adapt photosynthesis so that they only
open their stomata at night to absorb carbon dioxide, reducing water loss
 The plants store the carbon dioxide in cell vacuoles as malic acid. During the day, the malic
acid is transported to the chloroplast and converted back into carbon dioxide
 This is called CAM (crassulacean acid metabolism) photosynthesis
Mangroves survive living in high salinity environments:

 Behavioural adaptations
Behavioural adaptations
 Behavioural adaptations are actions performed by an organism in response to a stimulus
that improves its chances of survival
 For example: birds migrating to avoid extreme temperatures
Behavioural Adaptations of Mangrove Crabs
 Mangrove crabs burrow sideways into the soft mud to gain protection from both dehydration
and predators. They use the water in their burrows to keep their gills moist and keep away
from the hot sun
Movement Adaptations of Plants
 Plants generally do not move much, but they still do exhibit responses to stimuli. It is just
slow and subtle
 For example:
o sunflowers exhibit phototropism moving in response to sunlight and plant hormones
o The shy plant Mimosa pudica can change turgor pressure rapidly, collapsing leaves
inwards when touched by an insect or predator. This protects the plant from harm,
and is called nastic movement
Nastic Adaptations of Carnivorous Plants
 Venus fly traps and sundews grow in nutrient poor soil, especially lacking nitrates
 When trigger hairs are touched, these plants collapse leaves inwards, catching insects use
nastic movement
 The plants secrete enzymes to digest insects and release nitrates as liquid fertilizer for the
plants
3.2.2 investigate, through secondary sources, the observations and collection of data that were
obtained by Charles Darwin to support the Theory of Evolution by Natural Selection, for example:
 Finches of the Galapagos Islands
Observations of Charles Darwin
 The British naturalist Charles Darwin (1809-1882) suggested a persuasive argument to
explain the range of adaptations and biodiversity on Earth
 His ideas built on previous theories of evolution and was called the Theory of Evolution by
Natural Selection
Finches of the Galapagos Islands
 Darwin observed that the Galapagos Island finches had beaks adapted for specific types of
food
 Darwin reasoned that each of the finches evolved from a common ancestor
 He proposed that distinctive adaptations such as beak structure evolved in response to the
selection pressure of different food sources
 Australian flora and fauna
 Part 3: Theory of Evolution by Natural Selection
3..3.1 explain biological diversity in terms of the Theory of Evolution by Natural Selection by
examining the changes in and diversification of life since it first appeared on the Earth
Biodiversity
 Biodiversity is the variety of all forms of life on Earth, the diversity of the characteristics that
living organisms have and the variety of ecosystems of which they are components
o Genetic diversity is the total amount of genetic characteristics in a species
o Species diversity is the total number of species in a community
o Ecosystem diversity is the variation of different ecosystems in an area

Evolution
 Evolution is the change in living organisms overtime
 Recipe for evolution: variation, selection and time
Evolution by Natural Selection
 Charles Darwin and Alfred Wallace jointly proposed a mechanism for species change
 They did not work together but arrived at the same conclusion:
o Individuals within populations naturally possess variations in structure, behaviour
and/or functioning
o If these variations confer an advantage, organisms survive a change in the
environment. These organisms are able to reproduce and pass on their favourable
characteristics to future generations (later described as survival of the fittest)
Darwin’s Big Idea
 Darwin’s theory of Evolution by Natural Selection and Isolation has 4 main points:
o Variation
 In any population, there is variation within the species
 Variation comes about due to genetic changes or mutations; these are not
changes the individual organism has control over
o Natural selection
 Some organisms have variations in their features that make them better suited
than others to a changed environment
 If a population consists of a diverse range of individuals, then the populations
is better able to survive a sudden change in the environment
 This diversity allows some organisms to compete more successfully, and
survive and breed and therefore pass on their genes to the next generation
 This is, those individuals that compete successfully in the new environment
outlive those that do not have such variations, this is termed natural
selection
o Survival and reproduction
 In any population, there are offspring that do not reach maturity and
reproduce, possibly because they are not as well suited to their environment,
struggle to find adequate nutrition, are more vulnerable to predators etc, and
therefore their characteristics are not pass on
o Isolation
 If a population is isolated from the original population, individuals that have
variations that allow them to survive the changed conditions will reproduce
and pass on these characteristics
  Eventually the population becomes so different to the original and individuals
are no longer able to interbreed and produce fertile offspring – a new species
has evolved
3.3.2 analyse how an accumulation of microevolutionary changes can drive evolutionary changes and
speciation over time, for example:
 Evolution of the horse
Macro and microevolution
 Evolution can be considered over very long periods of time and over shorter periods of time
o Macroevolution takes place over millions of years and results in the arising of new
species
o Microevolution takes place over a shorter periods of time and results in changes
within populations, but it does not produce new species in the short term
 e.g. pepper moths – variation in the species
Microevolution over time leads to speciation
 microevolution involves changes in characteristics over short periods of time
 Mutation and natural selection are the main processes that drive microevolutionary change
 An accumulation of these changes over time can lead to speciation
o An example of microevolution is the modern day horse
 Through fossil evidence we know that it has developed from a small dog-
sized, forest-dwelling animal called Hyacotherium to the horse of today
Horse Fossils
 Modern horses are large animals with only one toe and a large cheek span
 There are fossils of many transitional forms – fossilised remains of horses with three toes and
intermediate cheek span
 Early horses were small animals with four toes, short legs and a narrow cheek span between
the front teeth and cheek teeth
Horse Teeth
 Early horses were browsers and ate fruit. They had cheek teeth capped with enamel very
similar to humans and other mammals
 Modern horses are grazers and eat grass. They have grinding cheek teeth that grow
continually throughout the horse’s life
Microevolution of the Horse
 Towards the end of the Oligocene, Earth started cooling and drying. Rainforest gradually
gave way to grassland
 This produced selective pressures for horse ancestors: change to grass for food, and less
bushes, undergrowth and shadows for hiding places. Running faster became a better defence
against predators
 Evolution of the platypus
Mammals, Marsupials and Monotremes
 Mammals are animals with hair or fur, that split into roughly 3 groups:
1. Placental mammals carry offspring in the uterus
e.g. humans and cats
 2. Marsupial mammals carry offspring in pouches
e.g. koala and kangaroo
3. Monotremes which lay eggs
e.g. echidna and platypus
Platypus Ancestors
 There are only a few specimens of platypus fossils
 Obdurodon dicksoni was a large, spoon-billed platypus
 Its skull is one of the most perfect fossils know from Riversleigh
 They probably fed on insect larvae, yabbies and other crustaceans, and perhaps small
vertebrate animals such as frogs and fish
 A closely related species monotrematum sudamericanum
 The animal has been reconstructed from fossil teeth
 Unlike the living platypus these fossil platypuses had functional molar teeth
3.3.3 explain, using examples, how Darwin and Wallace’s Theory of Evolution by Natural Selection
accounts for:
 Convergent evolution
 Divergent evolution
Darwin-Wallace theory
 Darwin and Wallace studied a large numbers of living organisms and observed that
similarities in structure were common. These similarities could be accounted for in one of two
ways:
1. Divergent evolution: the process by which organisms that are related look different due
to exposure of different selection pressures
2. Convergent evolution: the process by which organisms that do not have a common
ancestor develop similar features in response to similar selection pressures in their
environments
Divergent Evolution
Examples:
 Darwin’s finches diverge from a common body plan. Different selection pressure therefore
favoured some forms over others
 The rise of the variety of horse species is also typical
Convergent Evolution
 Placental mammals from North America and Europe show similarities to marsupials in
Australia
 The organisms have been exposed to similar selective pressures and have adaptations to
similar niches
o E.g. the echidna and hedgehog both have prickles and eat insects

3.3.4 Explain how punctuated equilibrium is different from the gradual process of natural selection
Darwin’s Theory
 Darwin’s theory of evolution by natural selection proposes that populations change slowly
and gradually over time.
  Therefore, in the fossil record we should see a gradual change, for any one group of organism,
from ancestor to descendent
 However, we have very few instances
o One example, is the evolution of the horse which shows a gradual change over 40
million years
Punctuated equilibrium
 The theory of punctuated equilibrium proposes that evolution occurs in short bursts of rapid
change, followed by long periods of stability within populations
 This theory was put forward based on fossil evidence: if evolutionary change is gradual, it
could be predicted that there would be fossilised remains showing these ongoing changes
 However, many fossilised remains how millions of years going without any noticeable
evolutionary change to most species
o E.g. Horseshoe crabs have remained almost unchanged for 445 million years

Gradualism VS Punctuated equilibrium

Both theories agree that evolution by natural selection occurs, but the question asked is whether is
occurs in short bursts of rapid changes, or gradually over a long period
Part 4: Evolution – the Evidence
3.4.1 investigate, using secondary sources, evidence in support of Darwin and Wallace’s Theory of
Evolution by Natural Selection, including but not limited to:
 Biochemical evidence, comparative anatomy, comparative embryology and biogeography
Biochemistry
 Biochemistry is the study of chemicals found in cells. This involves comparing the sequences
of the basic units that make up these chemicals in species that may share evolutionary
relationships
 When the biochemistry of organisms is compared, it shows that the more closely related the
organisms are, the more similar their proteins or DNA is, meaning that have a more recent
common ancestor
 Technologies which sequence macromolecules include:
1. Amino acid sequencing
 Proteins are found in every living cell as part of the cell
membrane and as enzymes in the cytoplasm
 Proteins are made up of amino acids. It is the number, type
and sequence of these amino acids that determines the type of
protein
 The sequence of amino acids in the protein is analysed and
similarities and differences between organisms are identified.
Similarities imply that the organism may have shared a common ancestor. Differences imply
that the organism has changed over time (evolved)
 The number of differences is proportional to the length
of time since the organisms separated. This information
is used to construct evolutionary trees, called
phylogenetic trees
o Humans and chimpanzees have identical
sequence of amino acids in their haemoglobin
 and so they are more closely related than humans and gibbons, were have three
differences

2. DNA-DNA hybridisation
 DNA-DNA hybridisation is based on the assumption that DNA
molecules of closely related species have a similar nucleotide
base order
 The process involves applying heat to a double stranded DNA
molecule which causes the complementary strands to separate
 One strand from one species is then combined with on strand
from another species to form a ‘hybrid’ DNA molecule. The
more closely matched the base pairs are, the strong the binding
of the strands
 Heat is once again applied, this time to determine how strongly
the bases have combined; higher temperatures are required to
separate hybrid strands that are more strongly combined
 Closely related species have a very similar order of nucleotide bases and so their DNA strands
combine more strongly than species that are distantly related

Comparative anatomy
 Comparative anatomy is the study of similarities and differences in structure (anatomy) in
different species of living organisms to determine their evolutionary relatedness
 more similarities in the structure implies that they must be separated from a common ancestor
more recently
Evidence of divergent evolution
 in organisms that are being compared, similarities in structure suggest descent from a
common ancestor, whereas differences in structure represent modifications – how organisms
have evolved to become different.
 This is typical of divergent evolution and the similarities are best explained by common
descent – that is, sharing a common ancestor
Pentadactyl limb
 The pentadactyl (five-digit) limbs of all vertebrates have the same basic bone plan, but show
modifications because they are used in different ways. This is an example of a homologous
feature
Evidence of convergent evolution
  Structures that differ greatly in their basic plan, are said to be analogous. They have started
off being very different and then have evolved independently to become similar, because they
were selected to be used for a similar purpose
 The presence of analogous features does not provide evidence for evolutionary relatedness,
but rather for evolution of structures to serve a common purpose in a common environment
o Example: the Australian echidna and European hedgehog have both developed
protective spines to discourage predation but in terms of most other structures, they
are dissimilar
Vestigial structures
 Vestigial structures are evolutionary remnants of body parts that no longer serve a useful
function within that population. The presence of a vestigial structure provides evidence of
common ancestry
o Example: the presence of a reduced tail (coccyx) in humans and the pelvic bones in
snakes, are difficult to explain unless they are structures that have become reduced
because they no longer carry out a useful function in that animal’s lifestyle
Comparative embryology
 Comparative embryology is the comparison of embryos of different species at early stages
of development
 Embryonic comparisons show that general features of groups of organisms appear early in
development. More specialised features, which distinguish the members of a group, appear
later in development

Vertebrate embryos
 Fish, amphibians, birds and mammals all show the presence of gill slits, and tails in
embryonic development
 The presence of gill slits suggest that they all descended from a common ancestor that lived in
an aquatic environment
 These slits develop into internal gills in fish, external gills in amphibians and Eustachian
tubes in mammals
Biogeography
 Biogeography is the study of the geographical distribution of organisms, both living and
extinct, across the world
 Darwin-Wallace theory of evolution proposes that, for a new species to arise, a group of
individuals must become isolated. If this is true, the new species should resemble species with
which they shared a habitat
o Australia’s unique mammals and flowering plants are believed to have arisen
because of isolation of the continent. Australian organisms show similarities to
fossils on other southern continents, evidence that they may have had a common
origin and later evolved
Flightless birds (ratites)
 Some distribution patterns are best explained by continental drift theory
o E.g. the present-day distribution of flightless birds suggests that these birds
originated from a common ancestor on Gondwana and that the different populations
evolved on the isolated continents as they drifted apart
 Techniques used to date fossils and the evidence produced
Fossil Evidence
 Palaeontology is the study of ancient life preserved in rocks (fossils)
 the fossil record is a catalogue of the occurrence and evolution of living organisms through
geological time
 unfortunately, the chance of an organism fossilising is small, therefore the fossil record is
incomplete
Relative dating
 relative dating relies on the assumption that fossils found higher in rock strata are younger
than the lower fossils, so fossils are dated relative to one another (actual age is not
determined). Techniques used:
o stratigraphy: relies on sedimentary rocks being formed in layers with the oldest
rocks at the bottom and the youngest at the top. Therefore, fossils contained in these
rocks would display the same trend
 o biostratigraphy: compares fossils in different strata. Index fossils are useful in
determining the rock strata in which they are found. The occurrence of a fossil within
two different rock locations indicates that the rock containing the fossil specimens
were deposited at about the same time
Absolute dating (radiometric dating)
 absolute dating enables the actual age of the specimen to be determined by measuring
proportions of naturally occurring radioactive elements (radioisotopes) that are present in the
specimen
o each radioisotope decays at a known fixed rate, called its half-life (time taken for half
the atoms to decay)
o if the half-life is plotted onto a graph, the decay forms an exponential curve
o the atom that undergoes radioactive decay is known as the parent nuclide and the
atom which is formed is known as the daughter nuclide

Radiocarbon dating
 carbon becomes radioactive in the atmosphere; the carbon atom, which normally has 6
neutrons (carbon-12), gains 2 neutrons (carbon-14)
 carbon-14 is unstable and therefore decays back to nitrogen-14 at a known rate
 since carbon-12 is stable, the amount will stay the same
 the proportion of C-14 to c-12 in a fossil tells us how long ago the plant or animal was alive
3.4.2 explain modern-day examples that demonstrate evolutionary change, for example:
 the cane toad
 antibiotic resistant strains of bacteria
Antibiotics
 antibiotics are chemicals that are able to inhibit the growth of bacteria or can destroy them.
They target the cell wall and inhibit bacterial metabolism
 the first antibiotic, penicillin has highly successful in treating many bacterial infections.
However, with the widespread use of antibiotics and the misuse and overuse, bacteria have
evolved strains that are resistant to many, if not all, of the antibiotics available today
Bacterial Reproduction
 bacteria reproduce by binary fission
 when conditions are favourable they can multiply rapidly with many generations reproducing
within a single da. Numbers of bacteria quickly enter the millions
 bacteria can also reproduce sexually through conjugation, in which they exchange genetic
material. This process can lead to variation in a population of bacteria
Antibiotic Resistant Strains
 when exposed to an antibiotic (the selection pressure), the bacteria that have variations that
are best suited to that environment (resistant to the antibiotic) will survive and reproduce
 therefore, the population will become more resistant to the antibiotics over generations
Example: Golden Staph (MRSA)
 Staphylococcus aureus (golden staph) is a bacterium that causes mostly mild skin infections,
but can cause serious har, when it infects the blood or lungs
 It has now evolved a strain called MRSA (methicillin-resistant S. aureus) that is resistant to
many of the antibiotics used to treat it
 Today many people are wary of hospitals de to the rapid rise in resistant bacteria. There are
many documented cases where a person has entered hospital for a minor infection and has
caught golden staph