Edexcel A-Level 2024 Biology A - Topic 6 :
Immunity, Infection and Forensics Exam
Questions and Answers
Which 5 factors are used to determine the time of death of a
mammal? - Answer>>• Extent of decomposition
• Stage of succession
• Forensic entomology
• Body temperature
• Degree of muscle contraction.
Describe the stages of decomposition. - Answer>>1) Autolysis
occurs - Enzymes in the gut start to break down the wall of the gut
and the surrounding area. As cells die, they release enzymes
which help break down tissues.
2) The loss of oxygen in tissues favours the growth of anaerobic
bacteria. The bacteria invade tissues and release more enzymes.
----------------------------------------------
After a few hours:
• Cells and tissues are broken down by enzymes and bacteria
present before death - turns skin green
Few days-weeks:
• Microorganisms decompose tissues and organs - produces
gasses which cause bloating.
• Skin blisters and falls off
Few weeks:
• tissues liquefy and seep into the area around the body causing
bloating and deflation
,Few months - years:
• Skeleton remains
Decades - centuries:
• Skeleton disintegrates - nothing left
How is extent of decomposition used to determine time of death?
- Answer>>Bodies in similar environmental conditions show
regular patterns of decay ( fresh → bloated → decaying → dry).
Therefore stage of decomposition can be used to determine how
long a body has been dead for.
Which factors affect the extent of decomposition? - Answer>>•
Mild heat - increases rate as enzymes activity increases
• Intense heat - decreases rate as enzymes become denatured
• Humidity - the more humid the quicker the rate. In extremely dry
conditions the process can stop completely (e.g. mummies).
• Presence of wounds - increases rate as bacteria are able to
enter more easily
How can stage of succession be used to determine time of death?
- Answer>>As the body decays, the species colonising the body
change - there is a succession in species. As there is a
predictable sequence of ecological succession, analysis of the
community of species present can be used to determine time of
death.
----------------------------------------------
1) Anaerobic bacteria thrive in the no oxygen and acidic (lactic
acid) conditions
2) Certain flies, such as blowflies arrive, they are attracted to the
moisture, smell and open wounds. They lay eggs on the carcass.
, 3) The eggs hatch, maggots eat the skin and tissue of the body,
this liquidises certain parts which the adult flies feed on
4) Beetles are attracted, they lay eggs and the grub that hatch eat
the maggots
5) Parasitic wasps lay eggs in the beetle and fly larvae
6) Eventually the body dries out and species such as cheese and
coffin flies are abundant
7) Dehydration continues, maggots can't survive. Beetles with
strong mandibles, such as carcass beetles move in and eat the
remaining muscles and connecting tissues
8) Finally mites and moth larvae digest the hair
----------------------------------------------
The season, weather, size and location of the body will influence
the type and number of species present.
How can forensic entomology be used to determine time of
death? - Answer>>• Each species of insects has a specific life
cycle:
Egg (1 day) → Larva (9 days) → Pupa ( 6 - 12 days) → Adult fly.
• By determining the age of insects on a corpse the time of death
can be determined.
• They collect the eggs, larvae and pupa found and let them grow
into adults to estimate how long the insects have been there.
• Mostly used for bodies 4 - 14 days old.
How can body temperature be used to determine time of death? -
Answer>>• After death the temperature of the body begins to
decrease from 37°C as exothermic metabolic reactions stop.
Immunity, Infection and Forensics Exam
Questions and Answers
Which 5 factors are used to determine the time of death of a
mammal? - Answer>>• Extent of decomposition
• Stage of succession
• Forensic entomology
• Body temperature
• Degree of muscle contraction.
Describe the stages of decomposition. - Answer>>1) Autolysis
occurs - Enzymes in the gut start to break down the wall of the gut
and the surrounding area. As cells die, they release enzymes
which help break down tissues.
2) The loss of oxygen in tissues favours the growth of anaerobic
bacteria. The bacteria invade tissues and release more enzymes.
----------------------------------------------
After a few hours:
• Cells and tissues are broken down by enzymes and bacteria
present before death - turns skin green
Few days-weeks:
• Microorganisms decompose tissues and organs - produces
gasses which cause bloating.
• Skin blisters and falls off
Few weeks:
• tissues liquefy and seep into the area around the body causing
bloating and deflation
,Few months - years:
• Skeleton remains
Decades - centuries:
• Skeleton disintegrates - nothing left
How is extent of decomposition used to determine time of death?
- Answer>>Bodies in similar environmental conditions show
regular patterns of decay ( fresh → bloated → decaying → dry).
Therefore stage of decomposition can be used to determine how
long a body has been dead for.
Which factors affect the extent of decomposition? - Answer>>•
Mild heat - increases rate as enzymes activity increases
• Intense heat - decreases rate as enzymes become denatured
• Humidity - the more humid the quicker the rate. In extremely dry
conditions the process can stop completely (e.g. mummies).
• Presence of wounds - increases rate as bacteria are able to
enter more easily
How can stage of succession be used to determine time of death?
- Answer>>As the body decays, the species colonising the body
change - there is a succession in species. As there is a
predictable sequence of ecological succession, analysis of the
community of species present can be used to determine time of
death.
----------------------------------------------
1) Anaerobic bacteria thrive in the no oxygen and acidic (lactic
acid) conditions
2) Certain flies, such as blowflies arrive, they are attracted to the
moisture, smell and open wounds. They lay eggs on the carcass.
, 3) The eggs hatch, maggots eat the skin and tissue of the body,
this liquidises certain parts which the adult flies feed on
4) Beetles are attracted, they lay eggs and the grub that hatch eat
the maggots
5) Parasitic wasps lay eggs in the beetle and fly larvae
6) Eventually the body dries out and species such as cheese and
coffin flies are abundant
7) Dehydration continues, maggots can't survive. Beetles with
strong mandibles, such as carcass beetles move in and eat the
remaining muscles and connecting tissues
8) Finally mites and moth larvae digest the hair
----------------------------------------------
The season, weather, size and location of the body will influence
the type and number of species present.
How can forensic entomology be used to determine time of
death? - Answer>>• Each species of insects has a specific life
cycle:
Egg (1 day) → Larva (9 days) → Pupa ( 6 - 12 days) → Adult fly.
• By determining the age of insects on a corpse the time of death
can be determined.
• They collect the eggs, larvae and pupa found and let them grow
into adults to estimate how long the insects have been there.
• Mostly used for bodies 4 - 14 days old.
How can body temperature be used to determine time of death? -
Answer>>• After death the temperature of the body begins to
decrease from 37°C as exothermic metabolic reactions stop.
