T6 Flashcards
What happens when plants and animals die?
Microorganisms surrounding them secrete enzymes that decompose dead organic matter into smaller molecules so they can respire.
What are the 5 ways scientists can estimate the time of death?
1) Body temperature
2) Degree of muscle contraction
3) Forensic entomology
4) Extent of decomposition
5) Stage of succession
Explain how body temperature is used in estimating TOD?
(Process of Algor Mortis).
Body heat (37 degrees) produced from respiration.
After TOD, Metabolic reactions slow down.
Temperature decreases and equates surroundings at approx 1.5 - 2 degrees per hour.
Factors such as air temperature, clothing, body weight can affect the cooling rate.
How the degree of muscle contraction affects TOD?
Rigor Mortis is the stiffening of muscles, 4-6 hours after death.
1) Oxygen can’t teach the muscles so they’re deprived of it.
2) Anaerobic Respiration therefore occurs.
3) Lactic acid is produced.
4) pH levels decreases due to lactic acid.
5) ATP can’t be produced as the enzymes that produce it are inhibited.
6) Stiffening of the muscles due to the Myosin and Actin becoming fixed.
A factor that affects Rigor Mortis?
Smaller muscles in the head contract first and larger muscles contract last.
Higher the temperature, faster Rigor Mortis occurs.
Wears off around 24-36 hours after TOD.
What is forensic entomology?
What are the factors affecting it?
When the body is quickly colonised by different variety of insects.
E.g. Flies are often the first to appear
Also identifying the stage of life cycle the insects in.
Factors like humidity, oxygen, temperature, drugs effect the insects.
Higher temperature means a faster metabolic rate.
How is the extent of decomposition used to estimate TOD?
Factors affecting decomposition?
Hours - few days: Body’s own enzymes and bacteria break down cells and tissues -> skin turns green.
Few days - few weeks: Microorganisms decompose the tissues and organs producing methane gas causing the body to become bloated -> skin blisters and peels off.
Few weeks - few months: Tissues begin to liquify and seep out into the area around the body.
Few months - few years: Only skeleton remains.
Decades - centuries: Skeleton disintegrates until there is nothing left on the body.
Factors include: Temperature, oxygen availability.
Explain how the different stages of succession can be used to estimate TOD?
Succession is how different organisms found in the dead body change over time.
Refer to forensic entomology.
Difference between succession in a dead body and plant succession?
Succession in a dead body, the early insects remain as other insects colonise it which doesn’t happen in plant succession.
Succession in general…
Pioneer species are the first species to colonise the area.
Secondary succession is when the initial environment is much harsher.
Last stage of succession is called the climax community and is more stable as the ground has more nutrients.
Structure of DNA?
It is made up of nucleotides.
Each nucleotide has 4 bases: ATCG.
A molecule of DNA consists of two strands of nucleotides joined together by complementary base pairing.
Contains the sugar Deoxyribose.
What is the process of DNA profiling?
1) DNA sample is obtained from blood, saliva, tissue.
2) PCR is used to amplify DNA, making millions of copies of specific regions.
3) A fluorescent tag is added to view the DNA under UV light.
4) Gel Electrophoresis is used to separate the DNA according to their length.
5) Gel is viewed under UV light and the DNA fragments appear as bands.
How a Polymerase Chain Reaction works? (PCR)
Clue: 955072
1) A reaction mixture that contains DNA sample, free nucleotides, primers and DNA polymerase.
Primers are short pieces of DNA that are complementary to the bases at the start of the fragment you want.
DNA polymerase is an enzyme that creates new DNA strands.
2) DNA heated to 95 degreases to break hydrogen bonds between 2 strands of DNA.
3) Mixture is then cooled to between 50 and 65 degrees so the primers can bind (anneal) to the strands.
4) The reaction mixture is then heated to 72 degrees so the DNA polymerase can work.
5) DNA polymerase lines up free nucleotides along each template strand where complementary base pairing happens.
6) So 2 new copies of the fragment of DNA are formed in one cycle of PCR.
Cycle repeated and each PCR cycle doubles the amount of DNA:
1st Cycle: 4 DNA fragments.
2nd Cycle: 8 DNA fragments.
3rd Cycle: 16 DNA fragments.
Explain how Gel Electrophoresis works?
1) DNA is placed into wells in a slab of Gel covered in buffer solution which conducts electricity.
2) Electrical current causes the negatively charged DNA fragments to move towards the anode (positive electrode).
3) Short DNA moves faster and travel further.
Purpose of DNA profiling?
Used in paternity tests as we inherit half our DNA from our parents.
Used in animals to prevent inbreeding which causes health and reproductive problems, and also decreases the gene pool.
What is a pathogen?
A pathogen is any organism that causes disease.
E.g. Bacteria, fungi, all viruses.
What is HIV?
Human Immunodeficiency Virus infects and destroys T helper cells (white blood cells) which are responsible for activating other immune system cells.
Why does HIV need a host T helper cell?
1) HIV is spread through infected bodily fluids meeting mucosal surfaces (genitals through sexual intercourse).
2) HIV can only reproduce inside of the T helper cells as it doesn’t contain enzymes and ribosomes.
What is the process of HIV replication?
1) Proteins attaches to receptor molecules on cell membrane of the T helper cell.
2) Capsid released into the cell where it reveals the genetic material (RNA) into cytoplasm.
3) Reverse transcriptase is used to make complementary strands of DNA from viral RNA template.
4) Double stranded DNA is made and inserted into human DNA.
5) Host T helper cell enzymes are used to make viral proteins from viral DNA.
6) Viral proteins are assembled into new viruses.
How does HIV cause AIDS?
AIDS is when the immune system deteriorates then fails as a result of the T helper cells decreasing.
Having AIDS makes you vulnerable and leads to opportunistic infections.
Symptoms of AIDS?
Minor infections of mucous.
Number of T helper cells decrease further meaning more chance of infection from opportunistic infections.
Process of how Bacterium Mycobacterium Tuberculosis causes Tuberculosis (TB)?
Infection starts when tiny droplets containing the bacteria are inhaled into the lungs.
1) Phagocytes in the lungs take up the bacteria.
2) Bacteria replicate inside the phagocytes.
3) The immune system seals off infected phagocytes in structures called tubercles.
4) Inside the tubercles, bacteria become dormant so no symptoms are shown.
5) Dormant bacteria may become reactivated and overcome immune system.
6) Reactivation is more likely with someone with a weakened immune system.
Symptoms of TB?
Inflammation of the lungs -> severe coughing
Damages lungs -> Respiratory failure -> death
Lungs -> brain and kidney -> organ failure -> death
How can pathogens enter the body?
Cuts in the skin.
Digestive system from contaminated food.
Respiratory system from inhalation.
Mucosal surfaces like nose, mouth, genitals.
What barriers exist to prevent infection?
1) Stomach Acid - Acid kills pathogens but some may survive.
2) Skin - A physical barrier preventing pathogens from entering the bloodstream.
3) Gut and Skin Flora - Covered in harmless microorganisms called flora. They compete with pathogens for nutrients and space, limiting the number of pathogens.
4) Lysosomes - Found in tears, saliva, mucus etc. It kills bacteria by damaging cell walls and it makes bacteria burst open.
