TOPIC 6

Question 1

How do these conditions of a peat bog allow preservation of a body? (2)

Lack of oxygen
Low temperatures

Answer 1

Lack of oxygen:
- microorganisms cannot respire body molecules aerobically

Low temperatures:
- decomposers enzymes below optimum temperature so activity is low

Question 2

Outline the stages of rigor mortis after death. (4)

Answer 2

• lack of oxygen so muscles respire anaerobically
• lactic acid produced, lowering pH
• low pH denatures enzymes
• muscle stiffness is the result.

Question 3

Describe the events during stage 1 of PCR. (3)

Answer 3

• DNA heated up to 95 deg
• H bonds b/w DNA strands break
• DNA molecules break apart into separate strands

Question 4

State 2 features that allow nucleic acid to be separated by gel electrophoresis. (2)

Answer 4

• net overall charge
• length of fragments

Question 5

Describe the 3 steps of PCR. (3)

Answer 5

Denaturation:
- DNA heated to higher temperatures to separate the 2 strands.

Annealing:
- DNA cooled, allowing primers to anneal to target sequence

Elongation:
- double stranded DNA synthesised by DNA polymerase

Question 6

Describe the process of DNA profiling. (4)

Answer 6

• isolate DNA from biological sample
• amplify DNA through PCR
• use restriction enzymes to cut up DNA into fragments
• DNA fragments form distinct band patterns unique to each individual.

Question 7

Describe how phagocytosis destroys pathogens. (4)

Answer 7

• phagocyte recognises foreign antigen
• virus engulfed by phagocyte
• virus enclosed in vacuole
• virus is digested

Question 8

Describe how T and B cells work together to combat infectious disease. (4)

Answer 8

• T cells bind to antigen
• T cells kill infected cells
• B cells combat infection in body fluids
• B cells secrete antibodies

Question 9

Explain the consequences of agglutination to the pathogen. (2)

Answer 9

• pathogens are tightly clumped so cannot exchange food
• so metabolic process stops and cells die

Question 10

Define: retrovirus. (1)

Answer 10

• a virus which can make DNA from RNA

Question 11

Explain how HIV can lead to death by bacteria. (4)

Answer 11

• HIV enters T-helper cells
• T-helper cells machinery taken over
• B cells no longer activated
• pneumonia can take hold and cause death.

Question 12

Compare and contrast the primary and secondary immune responses to an infection. (4)

Answer 12

Similarities:
- both produce antibodies

Differences:
- primary: plasma cells multiply quickly but slowly in secondary

• primary: causes symptoms, in secondary patient unaware of infection
• secondary immune response is stronger