Topic 6

Front 1

Polymerase is the…

Back 1

enzymeused in the Polymerase Chain Reaction to amplify DNA in a small sample of blood akenfrom a crime scene.

Front 2

Gel Electrophoresis is the …..

Back 2

processused to separate DNA fragments to create a DNA profile

Front 3

Describe how gel electrophoresis can be used to analyse DNA. (3

Back 3

First, a DNA sample will be collected from blood, saliva or semen etc; *thesesmall samples of DNA can then be amplified by PCR.DNA profiling then takes place which uses *restrictionenzymes to break the DNA and then *uses electropotential difference, with the DNA in a gel, to draw the bands apart.*The DNA is stained so it can be seen andwill *show up as bands/bars. *The number ofbands that match indicates the similarity of the DNA.

Front 4

UsingDNA profiling explain how a suspect is found guilty

Back 4

A DNA match is needed, thismeans that *all of the bands in the sample are the same as the ones shown inthe evidence sample. *DNA profiling assumes every individual’sDNA is unique/different; *apart from identical twins. *DNA profilinganalyses the introns/noncoding blocks/STRparts of DNA as the *non-coding areas are hypervariablebecause *there are a large number of introns/non-coding blocks and so there canbe *many combinations of STRs at each locus.

Front 5

Suggesthow DNA profiling could be useful to scientists who examine fossils of animalsand plants. (2)

Back 5

*Comparisons could be madebetween DNA from fossils and other organisms *to find geneticrelationships/how closely related they are. It may also be *used in taxonomy/classification *to understand evolutionary lines/to determine a common ancestor.

Front 6

Explainhow the results of DNA profiling of tissue samples from the two sub-speciescould be used to provide evidence that they share common ancestry. (3)

Back 6

DNA profiling will *produce bands thatwill have spread to *certain positions.*Common/similar bands will contain similar DNA fragments;*the more similar these patterns, the closer the relationship/more likely thesub-species will have a recent common ancestor. *There will still be very few differences between the DNA ofsub-species.

Front 7

Suggesthow DNA analysis could give further evidence for evolution. (2)

Back 7

DNA analysis could show the *similarity(of DNA) and indicate the closeness of a genetic relationship *becausegenes are sections of DNA and these *genes are the codes for proteins.

Front 8

Whycan’t species of plants be identified from woody (xylem) material using PCR andDNA profiling? (2)

Back 8

Because *xylem/wood is made of dead material/has no livingmaterial/cytoplasm/nuclei/ mitochondria, meaning *no DNA / nucleic acidis present in thematerial.

Front 9

Suggestwhy DNA polymerase from human sources is not suitable for use in a PCR machine.(2)

Back 9

*Because human enzymes will not work at high/ above37oCtemperatures due to *denaturation (change in shape of active site) at the temperatures found in thePCR (55-95◦C).

Front 10

Explain why evidence from DNA profiles may not be absolutely conclusive.(2)

Back 10

*DNA profiling has several stages and *artefacts/contamination can arise at any stage. Furthermoreas *only a few sequences/a small portion of DNA isanalysed it is *possible to get two identicalprofiles from unrelated individuals or for *identicaltwins/closely-related individuals to show the same profile. Thus the minimumamount to be analysed is 10STRs

Front 11

Thefirst stage in the decomposition of a cow pat is known as putrefaction. Explainhow carbon dioxide and ammonia are formed during this stage of decomposition. (4)

Back 11

*Microorganisms/microbes/bacteria/fungi are decomposers that *convert organic compounds to carbon dioxide and *nitrogencompounds/proteins/amino acids/urea to ammonia. *Aerobic/ anaerobic respiration *of the microorganisms/bacteria/fungiis the process whereby this occurs.

Front 12

Suggest why the time taken for a cow pat to decompose changes atdifferent times of the year. (3)

Back 12

*Because in the warmer times of the year the process will befaster as more heat energy is available and so kinetic energy is available forenzyme reactions/ to speed up the metabolism but less is available in thewinter months (temperature effect). *Therewill also need to be sufficient water availability forthe microorganisms to survive (*e.g. If frozen it cannot be accessed) however*too much water can lead to waterlogging whichreduces oxygen availability and thus the amount of energy produced fordecomposition.

There may also be *more insects/decomposers in summer. The *rate at which the microorganisms grow will also bea factor as it depends on how much food is available and how long they will bethere to decompose the pat.

Front 13

Suggest how woodlice are involved in the recycling of carbon.

Back 13

*The carbon/organic compounds in plant material are broken downin *digestion to provide respiratorysubstrates, *carbon dioxide is then released from them in respiration. *This carbon dioxide is available forphotosynthesis. The carbon consumed may alsobecome a part of the woodlice’s biomass untilit is eaten or dies and decomposes to release it.

Front 14

Describe the role of microorganisms in the recycling of the carbon fromcompounds in a dead animal.

Back 14

Decomposition/putrefaction occurs by microorganisms, they maydigest the carbon in the animal and then release the carbon into the atmosphereby *respiration where the *carbon dioxide isused for photosynthesis. *Methane is released in anaerobic conditions and is*available as fuel.

Front 15

Suggesttwoenvironmental factors that influence the rate of progress of rigor mortis in a muscleimmediately after death. (2)

Back 15

*Physical damage; *immersion in water; *(external) temperature;*burning; *electrocution; *clothing; *wind/air movements; *(Presence of drugs in the body:bio)

Front 16

Suggestwhy a forensic scientist would need to consider rigor mortis in several musclesof a body when estimating the time of death. (4)

Back 16

Because *not all muscleswill contract/relax/reach (full) rigor mortis at the same time; *e.g. jawmuscle will contract fully before the leg muscle. *Full contraction/rigor inmuscle does not last very long; for example the *leg is still contracting whilejaw is relaxing.

Front 17

Suggest how the timeof death of a white rhinoceros could be determined if it is discovered severaldays after being killed. (5)

Back 17

You could work out the time of death by looking at the*stage of successionon the body (if it has been a long period of time). You could also use *(forensic) entomology which involves identifying *the life cyclestages/ species of insect on the body *e.g. fly, beetle, wasp. You couldalso work out the time of death by looking at the *decompositionof the body as there are *different stages of decomposition.Decomposition involves *putrefaction (discolouration of abdomen that spreads), liquefactionof tissue, bloating and production of gases.*All of this information (insects, successionetc) is used to determine time of death,each of these method’s conclusions are *influenced by an external factor such as temperature thatinfluences the rate of succession/insect development/ decomposition.

Front 18

Suggest how Body Temperature would be useful in determiningthe time of death (2)

Back 18

*A drop in body temperature is linked to the amount of time that has passed afterdeath e.g. algor mortis, *many factorsaffect the temperature drop e.g. environmental temperature, body size,clothing. It is useful because *time of death can be calculated if the (ambient) temperature is knownhowever it is *only useful for a short period of time following death e.g. 24 hours/a day.

Front 19

Suggest how the state of decomposition would beuseful in determining the time of death (2)

Back 19

Because the *body decomposes in a specific sequence over time it can be useful indetermining time after death but *many factors affect the rate of decomposition e.g. environmentaltemperature or the presence of wounds. It will also *not be useful if all the body has decomposed.

Front 20

Interferon is the……

Back 20

enzymereleased in secretions to break down the cell walls of bacteria

Front 21

Histamine is the….

Back 21

chemical released by white cells in connective tissue that causesswelling

Front 22

Stages of Phagocytosis, a non specific response to bacterial infection

Back 22

Bacteria with antigens on surface enters bloo. Lymphocytes cells produce antibodies which bind to antigens. labelled bacteria attach to antibodies receptors on macrophage. Macrophage engulfs bacteria by forming vacuoles. Enzymes is released into the vacuoles to destroy the bacteria

Front 23

Explainwhy the processes shown in the flow diagram will only happen in response tosome types of bacteria. (3)

Back 23

Because the protein nature ofantigens/antibodies is different, the *antigensare specific to each bacteria strain and the *antibodies need to becomplementary/specific to the antigen so that binding can take place. *Somebacteria will have different/changed antigens to another, they may also havedifferent *slime/mucus capsules or be*inside body cells, this changes the effectiveness of the antibodies. This isalso a *primary infection meaning someantibodies are already present from passive immunity or breast feeding.

Front 24

Describe how the production and action of interferon differs from theproduction and action of lysozyme. (3)

Back 24

*Interferon is involved inviral infections, whereas lysozyme affects bacteria only. *Interferon isproduced only by infected cells, but lysozyme is present in all secretions(i.e. saliva/phagocytes/neutrophils/macrophages. They have different roles, *interferon inhibits replicationof viruses and lysozyme kills/ destroys bacteria.

Front 25

Suggestwhy the protein structure of lysozyme is important to the way in which it actsagainst pathogens. (4)

Back 25

*lysozyme is an enzyme and so it*has an active site with a specific shape for binding with our cell membranes.*The lysozyme acts on the cell wall *of bacteriaso that cell lysis occurs.

Front 26

Explainwhy an insect bite, which breaks the surface of the skin, may lead toinflammation around the injury. (3)

Back 26

Because *histamine is released as a result of damagedtissue/cells, *it is released from basophils/mastcells/platelets. *Histamine causes thearterioles to dilate (vasodilation), which increases blood flow andmakes the capillaries more permeable allowing phagocytes to reach the site moreeasily. *Inflammation involvesoedema/swelling/redness/heat/pain at the site of injury.

Front 27

Inorder to reduce inflammation, a cream containing antihistamines might beapplied to the skin, around an insect bite. Suggest why applying this creammight be better than taking tablets containing antihistamines. (3)

Back 27

Because inflammation is *only a local reaction produced/that histaminesproduced around the bite area and so *cream that has been applied to actualsite of production of histamine *will be more effective and have more rapid/ immediate relief as it will create a *higherconcentration of antihistamine at the site. *The antihistamines will not bedigested (by enzymes)/destroyed (by acid or enzymes) if they are applied in acream and not tablet. The *tablets may lower the immune response generally/leadto unpleasant side-effects.

Front 28

WhenMRSA enters the blood it can stimulate the production of several differentclones of plasma cells. These produce a variety of antibodies (polyclonalantibodies). Suggest an explanation for this. (4)

Back 28

Because the *bacterium is made of many differentpolymers/chemicals *which can act as different antigens, *individualB-lymphocytes will recognise specific antigens/antibodiesare specific and so only certain *B-lymphocytes are activated by T-lymphocytes. These cells of *B-lymphocytes will then divide by mitosis *to formgenetically identical plasma cells thatsecrete specific antibodies.

Front 29

Suggest the advantage of using monoclonal antibodies, rather thanpolyclonal antibodies, in the detection of antigens in the blood.

Back 29

Because a *specific antigen/virus/pathogen/bacterium can beidentified as the *specific/ monoclonal antibody binds to a specific antigen.As a result *specific treatment can be giventhat will *avoid unnecessary use of drugs/treatmentand will be *more likely to be effective.

Front 30

Statetwo characteristic features ofantibodies. (2)

Back 30

*They have glycoproteins in their cellwalls; have a *specific (3D) shape, L and H regions, Y-shape, 4(peptide) chains, disulphide bridges between peptides, hinge region; they also*have an antigen-binding site/variable region;all antibodies *have a similar/constant region; they are *produced by plasma cells/present on B cells;*their role is opsonisation, immobilisation,agglutination, lysis of foreign cells.