Dna: the Code of Life

Criterion 8 QA questions

DNA: THE CODE OF LIFE

Question

An aphid (pictured) is an insect which pierces the stem of plants and sucks the glucose from the phloem. It is a unique insect because the females can reproduce via sexual or asexual reproduction depending upon the environmental conditions.

a) Explain the difference between sexual and asexual reproduction. (2 marks)

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b) Outline: (2 marks)

i) the advantages of asexual reproduction.

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ii) the disadvantages of asexual reproduction.

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c) When the aphid reproduces sexually, the eggs are produced by meiosis. Describe the advantage the meiosis and fertilisation provide in terms of variety within the genepool. (3 marks)

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Question

Pedigrees are a diagrammatic way to represent the flow of genes through families. The pedigree below represents an autosomal dominant condition. The black shapes represent affected individuals.

a) Explain why individuals who have the trait, can have children without the trait.(1 mark)

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b) If two affected individuals had children, is there a chance that they could have an unaffected child? Use a Punnett Square to assist your response. Use BB to represent the dominant genotype and bb to represent the recessive genotype. (3 marks)

c) Examine the pedigree below. Explain how it is different from the one above in terms of the patterns of inheritance shown. (2 marks)

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d) The pedigree below shows a different pattern of inheritance.

i) Identify the pattern of inheritance. (1 mark)

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ii) Draw a Punnett Square to represent the mating shown at the arrow and determine the possibility of having any affected children. (4 marks)

Question

Human blood groups are polygenic and represented in the table below.

a) Explain the relationship between genotype and phenotype with reference to examples from the table. (2 marks)

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b) Draw a Punnett Square to represent the cross between a male with a heterozygous B blood type and a female with who is homozygous for the A blood type. (4 marks)

c) Human blood types are an example of co-dominance. Explain what this means and how it is different than incomplete dominance. Use examples to help your explanation. (4 marks)

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Natural Selection

Question

Peppered moths occur in England and Ireland. There are naturally two alleles which are expressed in the colouring of the moths: a light, speckled form and a dark, melanic form. Their populations have changed over time as shown in the graph below and these changes can be attributed to two events. Firstly, in the late 19th Century, industrialisation increased covering the local forests with soot and, secondly, at the end of the 20th Century a clean air act was legislated and the air quality all over Britain improved.

The peppered mothsexample is one of the most famous examples of natural selection.

a) Suggest a selective pressure that would have driven the changes in moth populations. Explain.

(2 marks)

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b) This example shows genetic drift. Explain, with reference to the moths, what that means.

(3 marks)

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c) The scientific name of the moths isBistonbetularia .

i) Explain what this represents according to the binomial system of nomenclature. (1 mark)

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ii) These moths are not separate species. Describe, with an example, what would have to happen for them to become separate species. (2 marks)

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d) The Galapagos Islands have several famous examples of evolution noted by Darwin. Some of these examples were fundamental in the development of his theory of evolution; survival of the fittest by natural selection.

Describe one example from the Galapagos Islands. (3 marks)

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MANAGING CHALLENGES

Organisms that cause disease

Question

The picture below is Aedesegypti, the mosquito which is responsible for transmitting Zika virus and dengue fever.

a) State the term used to describe organisms, such as this mosquito, that transmit diseases.

(1 mark)

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b) Malaria is another disease transmitted by mosquitoes. It is caused by a protist called Plasmodium. Distinguish between viruses and protists. (3 marks)

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c) The malaria Plasmodium is also considered a parasite. Outline the characteristic features of a parasite. (2 marks)

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d) The transmission of the malaria, Zika and dengue pathogens are all linked to the mosquitoes. Describe three other ways in which pathogens can be transmitted. (3 marks)

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e) Zika is an infectious disease. Using examples, explain how an infectious disease is different from a non-infectious disease. (3 marks)

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Lines of defence inside the body

Question

Poliomyelitis is an acute communicable disease of humans caused by a human enterovirus. Poliovirus is transmitted between people. When it multiplies in the nervous system, the virus can destroy the nerve cells which activate skeletal muscles resulting in paralysis. A poliovirus infection can provide lifelong immunity against the disease, however, protection is limited to the strain of the disease a person has had. In 1995, an inactivated polio vaccine was produced with all three strains of the disease and since then, a global effort to eradicate polio has been underway.

a) Describe how a person can acquire immunity.(2 marks)

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b) Mucous membranes, such as those that line the respiratory system and digestive system, provide environments suitable for pathogen colonisation. Describe how the body prevents pathogens from entering through these mucous membranes. Include any other mechanisms that could be used in conjunction with the mucous membranes. (3 marks)

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c) Distinguish between active and passive immunity. (2 marks)

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Question

Tetanus is caused by a toxin produced by bacteria called Clostridium tetani. These bacteria are commonly found in the environment within the soil, dust and manure. The bacteria can contaminate wounds, where they produce a toxin which causes symptoms of painful muscular contractions and spasms. Unvaccinated people are at risk of developing tetanus, especially if they have a deep cut or puncture wound. The time from exposure to the bacteria and the development of symptoms is usually about ten days, but it can take longer.

a) Explain how the body’s three lines of defence attempt to prevent a bacterial infection such as Clostridium tetani. (3 marks)

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b) Assuming a bacterial infection does occur, identify a treatment that would be available to the person with the infection. (1 mark)

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c) Explain how this response would have been different for a person who had been immunised against tetanus. (2 marks)

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Question

The first successful organ donation occurred in 1954 when an identical twin gave his brother a kidney. Prior to that, all organ transplants had been unsuccessful due unseen biochemical factors. Organ rejection was a continual problem until 1976 when it was discovered that cyclosporine was an effective immunosuppressant. Since then transplants have continued to have growing success around the world.

a) Explain why the early organ transplants were unsuccessful.(2 marks)

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b) The identical twins both survived the procedure. Explain why their operation was a success.

(2 marks)

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c) Describe the importance of the discovery of cyclosporine and the impact that it had on organ transplants since that time. (3 marks)

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