Purpose
To help you get your notes in order at the end of this topic.
Topic 6 summary
Make sure your notes cover the following points. The points are listed in the approximate order they appear within the topic. All the points are covered in the Student book, but where there is supporting information within the activities this is indicated.
There are suggestions on making notes and on revision in the Exam and Study Skills Support. You should:
Know how DNA can be amplified using the polymerase chain reaction (PCR). (Activity 6.1)
Use gel electrophoresis to separate DNA fragments of different lengths. (Activities 6.2 and 6.3)
Know how DNA profiling is used for identification and determining genetic relationships between organisms (plants and animals). (Activities 6.2, 6.4 and 6.5) (Checkpoint question 6.1)
Understand how to determine the time of death of a mammal by examining the extent of
decomposition, stage of succession, forensic entomology, body temperature and degree of muscle contraction. (Activity 6.5) (Checkpoint question 6.2)
Know the role of micro-organisms in the decomposition of organic matter and the recycling of carbon.
Be able to compare the structure of bacteria and viruses. (Activity 6.6) (Checkpoint question 6.3)
Understand the non-specific responses of the body to infection, including inflammation, lysozyme action, interferon and phagocytosis. (Activity 6.7) (Checkpoint question 6.4)
Understand the roles of antigens and antibodies in the body’s immune response, including the involvement of plasma cells, macrophages and antigen-presenting cells. (Activity 6.8)
(Checkpoint question 6.5)
Understand the differences between the roles of B cells (B memory and B effector cells) and T cells (T helper, T killer and T memory cells) in the body’s immune response (Activity 6.8) (Checkpoint question 6.5)
Understand how Mycobacterium tuberculosis (TB) and Human Immunodeficiency Virus (HIV) infect human cells, causing a sequence of symptoms that may result in death. (Activities 6.9, 6.11 and 6.17) (Checkpoint question 6.6)
Understand how one gene can give rise to more than one protein through post-transcriptional changes to messenger RNA (mRNA). (Activity 6.12 and 6.13)
Know the major routes pathogens may take when entering the body and understand the role of barriers in protecting the body from infection, including skin, stomach acid, and gut and skin flora. (Activity 6.14)
Understand how individuals may develop immunity (natural, artificial, active, passive). (Checkpoint question 6.7)
Investigate the effect of different antibiotics on bacteria. (Activity 6.15)
Understand the difference between bacteriostatic and bactericidal antibiotics. (Activity 6.16)
Understand how the theory of an ‘evolutionary race’ between pathogens and their hosts is supported by the evasion mechanisms shown by pathogens. (Activity 6.17)
Know how an understanding of the contributory causes of hospital-acquired infections have led to codes of practice regarding antibiotic prescription and hospital practice that relate to infection prevention and control. (Activity 6.17)
Salters-Nuffield Advanced Biology Resources
Topic 6 Exam-style End-of-topic Test Infection, Immunity and ForensicsTopic 6 Exam-style test
Instructions
Answer all questions in the spaces provided – there may be more space than you need.
Show your working in any calculation questions and include units in your answer where appropriate.
You may use a scientific calculator.
In questions marked with an asterisk (*), marks will be awarded for your ability to structure your answer logically showing how the points that you make are related or follow on from each other where appropriate.
Some questions must be answered with a cross in a box (). If you change your mind about an answer, put a line through the box () and then mark your new answer with a cross.
Information
The total mark for this paper is 45.
The marks for each question are shown in brackets – use this as a guide as to how much time to spend on each question.
Advice
Read each question carefully before you start to answer it.
Try to answer every question.
Check your answers if you have time at the end.
1 The table below gives a summary of the insects that might typically be found on a human corpse left in the open. Insect succession can be used as evidence in finding out the
approximate time of death in murder cases. This is sometimes called ‘fly-witness testimony’.
Stage Organism
Fresh (1 to 2 days)
Bluebottles (Calliphoridae) Flesh flies (Sarcophagidae) Bloated
(2 to 7 days)
Bluebottles (Calliphoridae) House flies (Muscidae) Flesh flies Sarcophaga spp. Decay
(5 to 13 days)
A variety of flies Beetles (Dermestidae) Post decay/dry stage
(10 to 23 days)
Various beetles
(a) Explain why the insects on a corpse change over time, as shown above. (2)
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Salters-Nuffield Advanced Biology Resources
Topic 6 Exam-style End-of-topic Test Infection, Immunity and Forensics(b) (i) Deduce the likely age of a corpse infested with flesh flies. (1)
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(ii) Give one reason why the exact age of a corpse infested with house flies cannot be given. (1) ……….……….…
(c) Explain how a more precise time of death, within the first week, could be determined using insect evidence. (2) ……….……….…
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(d) Give two other types of evidence, not involving insects, that might help to determine the time of death. (2) ……….……….…
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Salters-Nuffield Advanced Biology Resources
Topic 6 Exam-style End-of-topic Test Infection, Immunity and Forensics 2 Virus-infected cells are usually quickly destroyed by the human immune system. An infectedcell presents a piece of viral peptide on its surface, held by a special cell surface protein. T killer cells with the correct receptor bind to the presented peptides. The T killer cells then kill the infected cells.
(a) Explain how killing virus-infected cells helps to control infection in the
human body. (2)
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(b) State one disadvantage of T cells killing infected human cells. (1) ……….……….…
A person infected with human immunodeficiency virus (HIV) produces up to 109 new HIV particles every day. On average, each new virus contains one mutation. (c) Explain how a mutation of HIV could lead to the viral peptide presented by the infected cell being unrecognised by active T killer cells. (4) ……….……….… ……….……….… ……….……….… ……….……….… ……….……….… ……….……….… ……….……….…
Salters-Nuffield Advanced Biology Resources
Topic 6 Exam-style End-of-topic Test Infection, Immunity and Forensics(d) Give one reason why some mutations of HIV might reduce the rate of production of new virus particles. (1)
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(e) Explain the role of T memory cells. (2) ……….……….…
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(Total for question 2 = 10 marks) 3 Some bacteria and viruses are pathogens that cause human diseases.
(a) The diagram below shows a bacterium. Put a cross in the correct box to name
the four structures labelled in the diagram. (4)
cell wall ribosomes plasmid chromosome mitochondria A
B C D
Salters-Nuffield Advanced Biology Resources
Topic 6 Exam-style End-of-topic Test Infection, Immunity and Forensics(b) Compare and contrast bacteria and viruses. (5)
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Viruses use the protein synthesis machinery of the host cell to produce the peptides required to make new virus particles. (c) Describe the process of translating mRNA into a protein. (4) ……….……….… ……….……….… ……….……….… ……….……….… ……….……….… ……….……….… ……….……….…
Salters-Nuffield Advanced Biology Resources
Topic 6 Exam-style End-of-topic Test Infection, Immunity and Forensics 4 (a) Give two ways by which the human body prevents pathogens from entering theblood system. (2)
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(b) Describe the role of macrophages in non-specific immunity and specific immunity. (6) ……….……….… ……….……….… ……….……….… ……….……….… ……….……….… ……….……….… ……….……….… ……….……….… ……….……….… ……….……….… ……….……….… ……….……….…
Salters-Nuffield Advanced Biology Resources
Topic 6 Exam-style End-of-topic Test Infection, Immunity and Forensics 5 Bacteria were grown on an agar plate and incubated with four paper discs, each containing adifferent antibiotic. The plate after incubation is shown in the diagram below.
(a) Calculate the area of the zone around each disc with no bacteria. (2)
Answer A………..
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C……….
D………
(b) State which of the antibiotics is most effective at killing these bacteria and justify your answer. (2) ……….……….…
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(c) Antibiotic D is a much smaller molecule than antibiotic C. Explain why this method might not be appropriate when comparing the effectiveness of antibiotics C and D. (2) ……….……….…
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