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OCR Biology F212 Revision [3rd June 2013] (Now Closed) Watch

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    (Original post by Ambitions)
    Why do vaccines need to be continually updated? Apart from mutations... (for a 3 mark question say? )
    I think probably its because new strains of bacteria develop, and resistance to antibiotic occurs..something like that...different antigens?
    Haha Im not confident...
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    Argh T lymphocytes.
    Part of the humoral response, secondary defence.
    Pathogens that invade the human body display antigens.
    Phagocytes that engulf pathogens and infected cells become antigen displaying cells.
    T lymphocytes have receptors that are specific and complementary to antigens
    T lymphocytes bind to antigens on cell surface.
    This triggers colonal expansion, T lymphocytes multiply by mitosis.
    T lymphocytes then differenentiate into T killer cells and T helper cells.
    T killer cells cause pathogen death; receptors complementary to antigens bind to the pathogen. Kill by secreting toxic substances such as hydrogen peroxide into pathogenic cells.
    T helper cells secrete interleukins (or cytokines the two seem to be used interchangeably) which trigger the colonial expansion of B lymphocytes.

    Has that come up in a paper?


    Does anyone know the average raw mark for full ums conversion? Me and the ocr website aren't friends.
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    (Original post by mastermdc)
    Huh? In my book, it says that only phagocytes (Macrophages and Neutrophils) engulf cells. It says that T-killer cells secrete toxic substances such as hydrogen peroxide to kill the cell. Is this wrong?
    yes sorryy being silly yeah phagocytes engluf pathogens. T killer cells are what destroyes the infected cells that stimulated the humoral response.
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    Outline the Roles of DNA in living organisms. (6 marks)

    Any Help appreciated!
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    (Original post by SheriB)
    Did the january 2013 paper..just got a D..feeling very confident for the exam..not
    similarities and difference between Starch and cellulose?
    Don't worry about the D...just make sure you concentrate really hard and the knowledge will come to you

    Starch -
    Made up of alpha glucose
    Coiled
    Made of straigh chain amylose
    Branched
    (starch is energy store in plants)

    Cellulose -
    Beta glucose
    Straight chains
    Has microfibrils (cross linked)
    (forms plants cell wall - gives structure)
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    (Original post by Ambitions)
    Why do vaccines need to be continually updated? Apart from mutations... (for a 3 mark question say? )
    Say if the vaccine is for malaria....
    1) There are many different strains/species of malaria
    2) The antigens on the malarial virus continue to change shape due to mutation
    *3) There is more than one stage in the life cycle of malaria within the human (and different stages have different antigens)
    4) Therefore a different vaccine is needed for each strain/stage

    *This is specifically for malaria, but the other 3 points should be the same basic foundations for any other virus
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    (Original post by YouKnowMyName)
    Question:

    Explain the link between classification and phylogeny
    We use phylogeny (studing evolutionary relationships) to put different animals into groups, a way of classifying them. we use Cytochrome c, DNA and RNA to find common ancestors and the phylogeny of a animal and can therefore place them into a group according to the base sequence of nucleotides when comparing two animals of the same kingdom or phylum. Or the sequence of amino acids in the polypeptide
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    What does B lymphocytes do?
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    (Original post by Beni24)
    During Semi-conservative replication does the DNA polymerase help break the hydrogen bonds between the bases apart? Or does it help during Proteinsynthesis? Or is it used for both?
    It joins the sugar-phosphate backbone. This is from a mark scheme
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    The answer in a past paper for induced fit hypothesis was something like:
    The substrate binds to the active site forming an enzyme substrate complex. Active site changes shape creating a closer fit between substrate and active sit. Pressure applied destabilises bonds in the substrate which reduces the activation energy. Products are formed which no longer are complementary to the active site, products leave the active site. x
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    (Original post by Saif95)
    I think probably its because new strains of bacteria develop, and resistance to antibiotic occurs..something like that...different antigens?
    Haha Im not confident...
    ahaha, thats sometimes how I structure my answers in exam papers :P
    and ooo, thats true, but I was thinking more in the lines of viral infections like influenza vaccinations... do they develop resistance?
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    (Original post by the A* guy)
    Outline the Roles of DNA in living organisms. (6 marks)

    Any Help appreciated!
    DNA is used for coding for a sequence of amino acids...which form the primary structure. This coils to form the secondary structure (alpha helix and beta pleated sheets) held together by Hydrogen bonds. Tertiary structure can be formed

    It stores genetic information
    dna codes for mRNA , tRNA and rRNA
    making new cells
    long term store

    Are you sure they didn't also ask you for RNA? In which case you talk about protein synthesis

    Because I am curious now as to why this is 6 marks!
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    (Original post by Beni24)
    What does B lymphocytes do?
    B lymphocytes differentiate to become memory cells or plasma cells

    Plasma cells produce antibodies
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    What is the chance we could get a long question (8) marks comparing the action of B and T lymphocytes?

    - that would give us the chance to talk about T mature in thymus, B have antibodies on the surface but T have receptors, T action kills other cells but B doesnt, both produce memory cells
    and stuff like that?

    that would be a fab question
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    (Original post by Juliajuliajulia)
    Argh T lymphocytes.
    Part of the humoral response, secondary defence.
    Pathogens that invade the human body display antigens.
    Phagocytes that engulf pathogens and infected cells become antigen displaying cells.
    T lymphocytes have receptors that are specific and complementary to antigens
    T lymphocytes bind to antigens on cell surface.
    This triggers colonal expansion, T lymphocytes multiply by mitosis.
    T lymphocytes then differenentiate into T killer cells and T helper cells.
    T killer cells cause pathogen death; receptors complementary to antigens bind to the pathogen. Kill by secreting toxic substances such as hydrogen peroxide into pathogenic cells.
    T helper cells secrete interleukins (or cytokines the two seem to be used interchangeably) which trigger the colonial expansion of B lymphocytes.

    Has that come up in a paper?


    Does anyone know the average raw mark for full ums conversion? Me and the ocr website aren't friends.

    OCR doesn't have a UMS converter on their website annoyingly (unlike Edxexcel and AQA). But I heard that 86 has been the highest for 150 UMS?

    So quite decent!!
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    (Original post by samiwami)
    Don't worry about the D...just make sure you concentrate really hard and the knowledge will come to you

    Starch -
    Made up of alpha glucose
    Coiled
    Made of straigh chain amylose
    Branched
    (starch is energy store in plants)

    Cellulose -
    Beta glucose
    Straight chains
    Has microfibrils (cross linked)
    (forms plants cell wall - gives structure)
    i would say starch is made from amylose and amylopectin which both form alpha helix structures, not just starch is coiled.

    You may not get the mark for saying coiled cause you can have a left handed helix which is the structure collagen
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    What makes Structure relevant for its function ?
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    Do we have to relate structure to function for DNA? e.g. hydrogen bonds, sugar phosphate backbone, double helix and how these relate to the function of DNA
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    Quick query, in the Jan 2013 paper there was a question on the number of species in the world. I put that speciation is an ongoing process and so the number of species is constantly increasing, yet the mark scheme specifically said 'IGNORE refs to speciation' and accepted 'concept of species, difficult to define' (BS). Anyone know why this was the case? Ignoring the quality of OCR's exam writers :rolleyes: ...
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    A low Simpsons index gerally means the habitat has a low species richness which means it is very unstable and even a small change (or a massive one eg the development) would damage the species there either killing them or reducing their numbers substancially

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