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Revision 8. DNA Deoxyribonucleic acid or DNA has been described as the chemical basis of heredity. Discuss present-day concepts regarding its: chemical.

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Presentation on theme: "Revision 8. DNA Deoxyribonucleic acid or DNA has been described as the chemical basis of heredity. Discuss present-day concepts regarding its: chemical."— Presentation transcript:

1 Revision 8

2 DNA Deoxyribonucleic acid or DNA has been described as the chemical basis of heredity. Discuss present-day concepts regarding its: chemical nature and physical structuremode of duplication relationship to protein synthesis

3 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

4 Structure of DNA DNA is a coiled double helix made up of nucleotides on a sugar phosphate backbone

5 DNA is made of nucleotides

6 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

7 DNA controls protein synthesis

8 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.

9 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.

10 Extended answer d 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.

11 Extended answer d 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

12 Extended answer d "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.

13 Extended answer d "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

14 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 monthsSwamps and lakes – 9 months Snakes No snakes

15 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 Swamps and lakes – 9 months Snakes No snakes 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 interbreeding  new species has arisen

16 Extended answer b Using examples of natural selection in action, explain how selective forces in the environment contribute to evolutionary change.

17 Extended answer b Using examples of natural selection in action, explain how selective forces in the environment contribute to evolutionary change. Remember VOSSSIC: Variation Overpopulation  Struggle for survival Selection pressures  Survival of the fittest 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 Examples: Peppered moths Antibiotic resistance in bacteria Resistance to pesticide in insects Resistance to Myxomatosis or Calicivirus in rabbits


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