A-level human biology question paper unit 3 - pathogens and disease january 2009

General Certificate of EducationJanuary 2009Advanced Subsidiary Examination HUMAN BIOLOGY (SPECIFICATION A)
Pathogens and Disease
For this paper you must have:
a ruler with millimetre measurements.
Instructions
● Use black ink or black ball-point pen.
● Fill in the boxes at the top of this page.
● Answer all questions.
● You must answer the questions in the spaces provided. Answers
written in margins or on blank pages will not be marked.
● If you need extra space use page 20 for your answers.
● Do all rough work in this book. Cross through any work you do not Information
● The maximum mark for this paper is 75.
● The marks for questions are shown in brackets.
● You will be marked on your ability to use good English, to organise information clearly and to use accurate scientific terminology whereappropriate.
Answer all questions in the spaces provided.
mRNA may be described as a polymer. Explain why.
The diagram shows part of an mRNA molecule. It also shows the amino acids forwhich it codes.
C G A A A G C G C
The genetic code is non-overlapping and degenerate. Use the diagram to explain whatis meant by the code being The table shows the percentages of different bases in two molecules of mRNA
obtained from the same cell. Molecule X was transcribed from the DNA in one
chromosome. Molecule Y was transcribed from the DNA in a different chromosome.
Molecule X
Molecule Y
Name base Z.
Complete the table by writing in the percentages of base Z in molecules X
and Y.
(iii) The percentages of bases in molecule X are different from the percentages of
bases in molecule Y. Explain how transcription from DNA causes this
difference.
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Bacteria and parasitic flukes, such as Schistosoma, cause disease in humans.
Give two ways in which disease-causing bacteria may harm the body.
The diagram shows the life cycle of Schistosoma.
Name the secondary host of Schistosoma.
Explain how each of the following is an adaptation to the way of life of Schistosoma.
The larvae that leave the secondary host swim towards warm objects.
The adult flukes cover themselves with molecules from the host’s red blood cells.
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The diagram shows how mitosis and meiosis are involved in the formation of spermcells in a human.
Cell A contains two copies of a gene for brown eyes. How many copies of this gene
are there in
cell B at the start of interphase
(iii) a white blood cell from this person? During mitosis chromosomes line up on the equator of the cell. Each chromosomeconsists of a pair of chromatids. Each chromatid then moves towards a pole of the cell.
The graph shows how the distance between a centromere and the equator of the cellchanges during mitosis.
Sketch a curve on the graph to show the change in the distance apart of thecentromeres on a pair of chromatids during this mitotic division.
What phase of mitosis is represented by stage H on the graph?
(iii) What causes the distance between the centromere and the equator to change during stage G?
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Scientists investigated the growth of a population of bacteria in a fermenter. The fermenterwas kept at a constant temperature of 20 °C. Some of their results are shown in the graph.
The scientists sterilised the fermenter at the start of the investigation. Explain why.
Calculate the rate of increase of the dry mass of the bacteria between0 and 20 hours. Show your working and give your answer in g dm–3 h–1.
Explain the shape of the curve for the concentration of glucose in the culturemedium between 20 and 60 hours.
The optimum temperature for the growth of these bacteria is 35 °C.
On the graph, sketch a curve to show the dry mass of bacteria with the fermenter keptat 30 °C instead of 20 °C.
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Figure 1 shows an antibody molecule.
Hinge region affectsdistance between bindingsites Antibodies bind to antigens. Suggest how the hinge region is important in allowing anantibody to bind to more than one antigen.
Figure 2 shows part of two different antigen molecules.
Antigen X
Antigen Y
Explain why the antibody in Figure 1 will bind to antigen X but it will not bind to
antigen Y.
In 1796, Edward Jenner inoculated a boy with cowpox virus. Jenner later showed thatthe boy did not develop smallpox when he was exposed to the smallpox virus. Explainwhy the boy did not develop smallpox.
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Haemophilia is a disease in which the blood clots slowly. One form of haemophilia iscaused because a person cannot make a protein called Factor IX.
Figure 3 shows part of the gene for Factor IX. The arrows show where the gene is cut
by a restriction endonuclease called Taq1.
Explain why Taq1 only cuts the gene at these points.
Figure 4 shows part of the same gene from a person with this form of haemophilia. It
has also been cut with Taq1. The arrows show where Taq1 cuts the gene in this
person.
Explain why Taq1 cuts the gene shown in Figure 4 into fewer fragments.
A hospital technician took samples of DNA from a healthy person and a person whohad this form of haemophilia. She cut the two samples of DNA with Taq1 andseparated the fragments by electrophoresis.
Explain why electrophoresis separates the fragments from these samples ofDNA.
The technician used a DNA probe to locate the fragments once they had beenseparated. What is a DNA probe? Turn over for the next question
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Tetracycline is a bacteriostatic antibiotic. It is effective against many species ofbacteria but it does not affect human cells. When a person has a bacterial infectionand is treated with tetracycline, the concentration of tetracycline in the person’s cellsis much lower than that in the bacterial cells. Once inside a bacterial cell, tetracyclineprevents the binding of tRNA to mRNA.
Scientists have recently discovered a worrying feature about tetracycline. It increasesthe transfer of antibiotic resistance genes from one species of bacterium to another.
Use information from the passage and your own knowledge to answer the questions.
Tetracycline is an example of a bacteriostatic antibiotic (line 1). Explain whytetracycline is described as bacteriostatic.
Tetracycline is effective against many species of bacteria (lines 1 to 2). Explainwhy it is effective against many species.
When a person has a bacterial infection and is treated with tetracycline, theconcentration of tetracycline in the person’s cells is much lower than that in thebacterial cells (lines 3 to 4).
Suggest why the concentration of tetracycline is low in the person’s cells.
Explain what is meant by an antibiotic resistance gene (line 7).
Increasing the transfer of antibiotic resistance genes from one species ofbacterium to another is described as a worrying feature (lines 6 to 7). Explainwhy it is a worrying feature.
Apart from preventing protein synthesis, explain how antibiotics may be effectiveagainst bacterial infections.
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The flow chart shows how atheroma may lead to the formation of fibrin inside an artery.
Cells underneath epithelium ofartery are exposed to the blood Complete the flow chart by writing in the names of substances A and B.
Explain how each of the following prevents a sample of blood from clotting.
A substance that removes calcium ions is added.
The blood sample is cooled to 0 °C.
Nicotine is found in cigarette smoke. Nicotine increases blood pressure and itincreases the amount of fibrinogen in the blood.
Explain why people with atheroma are at a greater risk of a myocardial infarction ifthey smoke.
Question 8 continues on the next page
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There are various risk factors that increase the probability of men developing coronaryheart disease (CHD). The chart shows the effect of exposure to various combinationsof risk factors over a period of 10 years.
Describe the information given in the chart about the effect of smoking on theprobability of a man developing coronary heart disease.
Does the evidence in columns 1 and 2 of the chart prove that a systolic bloodpressure of 22 kPa causes coronary heart disease? Explain your answer.
END OF QUESTIONS
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