How do these conditions of a peat bog allow preservation of a body? (2)
Lack of oxygen
Low temperatures
Lack of oxygen:
- microorganisms cannot respire body molecules aerobically
Low temperatures:
- decomposers enzymes below optimum temperature so activity is low
Outline the stages of rigor mortis after death. (4)
- lack of oxygen so muscles respire anaerobically
- lactic acid produced, lowering pH
- low pH denatures enzymes
- muscle stiffness is the result.
Describe the events during stage 1 of PCR. (3)
- DNA heated up to 95 deg
- H bonds b/w DNA strands break
- DNA molecules break apart into separate strands
State 2 features that allow nucleic acid to be separated by gel electrophoresis. (2)
- net overall charge
- length of fragments
Describe the 3 steps of PCR. (3)
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
Describe the process of DNA profiling. (4)
- 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.
Describe how phagocytosis destroys pathogens. (4)
- phagocyte recognises foreign antigen
- virus engulfed by phagocyte
- virus enclosed in vacuole
- virus is digested
Describe how T and B cells work together to combat infectious disease. (4)
- T cells bind to antigen
- T cells kill infected cells
- B cells combat infection in body fluids
- B cells secrete antibodies
Explain the consequences of agglutination to the pathogen. (2)
- pathogens are tightly clumped so cannot exchange food
- so metabolic process stops and cells die
Define: retrovirus. (1)
- a virus which can make DNA from RNA
Explain how HIV can lead to death by bacteria. (4)
- HIV enters T-helper cells
- T-helper cells machinery taken over
- B cells no longer activated
- pneumonia can take hold and cause death.
Compare and contrast the primary and secondary immune responses to an infection. (4)
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
