Transcript Revision 8

Revision 8
DNA
Deoxyribonucleic acid or DNA has been described as the chemical basis of
heredity. Discuss present-day concepts regarding its:
chemical nature and physical structure
mode of duplication
relationship to protein synthesis
Why is DNA important
• It can be inherited (passed on in cell
divisions)
• It can easily be copied with a high degree
of accuracy
• It controls which proteins are made
Structure of DNA
DNA is a coiled double helix made up of nucleotides
on a sugar phosphate backbone
DNA is made of nucleotides
DNA replication
• Occurs in interphase – before
mitosis starts
• One set of enzymes split the
strands
• Another set of enzymes join new
nucleotides to each strand
• Nucleotides match up by the
base pairing rule (C – G, A - T)
• The end result is two identical
strands, joined at a point called
the centromere
DNA controls protein synthesis
Multiple choice 3
Some scientists are concerned that the effects of greenhouse gases may be
worse than we think. Which of the following would help to reduce or mask
the measurable effects of greenhouse gases?
a) Smog and haze in the atmosphere reduce the amount of solar radiation
reaching the Earth's surface.
b) The clearing and burning of forests adds more carbon dioxide to the
atmosphere.
c) Birth rates of humans are falling in most countries.
d) Use of renewable energy sources is increasing.
The open ocean can be divided into an upper zone where primary productivity
occurs and a lower zone where it does not. What is largely responsible
for the difference?
a) The upper zone is sufficiently warm for photosynthesis.
b) The upper zone has sufficient light for photosynthesis.
c) The lower zone has a high density of consumers that eat all the producers.
d) The lower zone lacks producers and therefore nothing can live there.
Multiple choice 3
Some scientists are concerned that the effects of greenhouse gases may be
worse than we think. Which of the following would help to reduce or mask
the measurable effects of greenhouse gases?
a) Smog and haze in the atmosphere reduce the amount of solar radiation
reaching the Earth's surface.
b) The clearing and burning of forests adds more carbon dioxide to the
atmosphere.
c) Birth rates of humans are falling in most countries.
d) Use of renewable energy sources is increasing.
The open ocean can be divided into an upper zone where primary productivity
occurs and a lower zone where it does not. What is largely responsible
for the difference?
a) The upper zone is sufficiently warm for photosynthesis.
b) The upper zone has sufficient light for photosynthesis.
c) The lower zone has a high density of consumers that eat all the producers.
d) The lower zone lacks producers and therefore nothing can live there.
Extended answer 2003 36d
Ecosystems around the world are under threat from growth in human
populations and many species are in danger of extinction. Present a
rationale for conserving natural ecosystems and give brief examples of how
biological knowledge can be applied in effective conservation.
Extended answer 2003 36d
Ecosystems around the world are under threat from growth in human populations and many species are in
danger of extinction. Present a rationale for conserving natural ecosystems and give brief examples of
how biological knowledge can be applied in effective conservation.
• cultural heritage issues
• aesthetics – people enjoy and wish to keep beautiful organisms/places
• ethics – do humans have the right to destroy other species?
• intergenerational equity – future generations have a right to the same resources/access to ecosystems
• economics – biodiversity may be useful for drugs, products
• biodiversity may be useful for tourism
• ecosystem stability – food web, nutrient cycles, mutualism
• removal of keystone species may cause collapse
• natural ecosystems provide valuable services
• conserving biodiversity
• water tables/salinity
• prevention of extinctions
maximum of 6 marks for the above points
• protection laws
• captive breeding
• feral pests/disease control
• national parks
• reafforestation
• reintroductions
• culling programmes
• decrease or control pollution
maximum of 6 marks for the above points – describing how each works/knowledge needed
Extended answer 2005 37d
"The cane toad (Bufo marinus) was introduced into Australia in 1935 to control the sugar
cane beetle, but it proved ineffective. For the past 60 years, cane toads have been
expanding their territory in Australia, and are capable of colonising at least four of the
mainland Australian states, [including Western Australia]. As the toad's geographical
range continues to expand, concern has increased about their detrimental
environmental effects, particularly on the wetlands of the Northern Territory. Studies
into the feasibility of biological control have commenced."
(i) What steps should have been taken before the cane toad was first introduced in 1935
to prevent it from becoming a pest?
(ii) Discuss, using examples of successful and unsuccessful biological controls, the kinds
of biological controls that might be used to control the cane toad in the future.
Extended answer 2005 37d
"The cane toad (Bufo marinus) was introduced into Australia in 1935 to control the sugar cane beetle, but it
proved ineffective. For the past 60 years, cane toads have been expanding their territory in Australia, and
are capable of colonising at least four of the mainland Australian states, [including Western Australia]. As
the toad's geographical range continues to expand, concern has increased about their detrimental
environmental effects, particularly on the wetlands of the Northern Territory. Studies into the feasibility of
biological control have commenced."
(i) What steps should have been taken before the cane toad was first introduced in 1935 to prevent it from
becoming a pest?
Check that control agent is:
• specific for pest only
• not poisonous to native spp
• able to do job expected
• not a competitor of native spp that have come to rely on introduced pest as food source
• release in quarantine/isolated area first
• unlikely to introduce an exotic disease
•
research species/research country of origin
(Maximum 6 marks)
(ii) Discuss, using examples of successful and unsuccessful biological controls, the kinds of biological controls
that might be used to control the cane toad in the future.
Types of biological control:
• Predator: to kill and eat pest eg Cactoblastis eats prickly pear, lady birds kill insects
• Parasite: to weaken, kill or sterilise pest
• Competitor: to limit resources available to pest
• Disease eg Calici virus kills rabbits
• Sterilize males eg fruit flies
• Named successful example
• Named unsuccessful example
(Maximum 6 marks)
Maximum 10 marks total
Natural selection
Once upon a time, on an island off the North-West coast of Europe, there lived a
small frog called Crinea rotunda. This animal was similar to a tree frog but was
spherical in shape. It lived all over the island.
Early settlers divided the island in half by erecting a fence that snakes could not
cross.
Today, visitors to the island will only fin C. rotunda on the western side. On the
eastern side there is a similar animal except it is not spherical, as it has more
“normal” frog shape. Breeding experiments between the two types of frogs
have resulted in no fertile offspring being produced.
Using this information, and the map below, explain the likely steps that must have
happened for this situation to have occurred. Include gene frequencies,
isolating mechanisms, natural selection etc.
Swamps – 2 months
Snakes
Swamps and lakes – 9 months
No snakes
Natural selection
Once upon a time, on an island off the North-West coast of Europe, there lived a small frog called Crinea
rotunda. This animal was similar to a tree frog but was spherical in shape. It lived all over the island.
Early settlers divided the island in half by erecting a fence that snakes could not cross.
Today, visitors to the island will only fin C. rotunda on the western side. On the eastern side there is a
similar animal except it is not spherical, as it has more “normal” frog shape. Breeding experiments
between the two types of frogs have resulted in no fertile offspring being produced.
Using this information, and the map below, explain the likely steps that must have happened for this
situation to have occurred. Include gene frequencies, isolating mechanisms, natural selection etc.
Variation must have existed in original population – spherical & normal shape
Spherical variation gives advantage under certain conditions (eg drying out/predation by snakes
Before separation selection pressures favour spherical shape over the entire island
Fence acts as geographical barrier  isolation of 2 populations
Each side now has different selection pressures
On western side – selection pressures (snakes or
drying out) favour spherical shape
On eastern side there is more water & human presence
- so no snakes & possibly different food/pollution effects
– so spherical shape is not selected for
Over time, the gene frequencies change – western side
has larger frequency of spherical shape, eastern side
has larger frequency or spherical shape
After sufficient time populations no longer capable of
Snakes
interbreeding  new species has arisen
No snakes
Swamps – 2 months
Swamps and lakes – 9 months
Extended answer 2004 36b
Using examples of natural selection in action, explain how selective
forces in the environment contribute to evolutionary change.
Extended answer 2004 36b
Using examples of natural selection in action, explain how selective forces in the
environment contribute to evolutionary change.
Examples:
Remember VOSSSIC:
Peppered moths
Variation
Antibiotic resistance in bacteria
Overpopulation  Struggle for survival
Resistance to pesticide in insects
Resistance to Myxomatosis or
Selection pressures  Survival of the fittest
Calicivirus in rabbits
Inheritance  Changes in gene frequencies
• the environment provides the selective force
• natural selection requires variation in populations
• variation arises from mutation
• variation arises from recombination/crossing over/independent assortment
• variation is genetic (inherited)
• natural selection requires differential survival of variants
• the best-adapted variants survive and reproduce
• evolutionary change occurs over considerable time/many generations
• natural selection can lead to speciation/change in gene frequencies
• example showing initial variation, how the gene pool changes, survival of the fittest and
identification of the selective force (maximum 4 marks)
• second example showing initial variation, how the gene pool changes