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

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    Did anyone else think that the 'water bear' of the last question was a real bear :') ? Also would this have made a difference in terms of marks?


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    (Original post by Kamal_Voltaic)
    There was this one 2 mark question that I just couldn't answer. Something about how the phagocyte gets from the bloodstream to the lymphatic system?
    The rest of it was alright.
    Histamine. Apparently it makes the capillaries more leaky and fluid passes into the lymphatic system or something like that. I wrote that. :/
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    (Original post by MedMed12)
    the the RNA different to DNA could I say ribose sugar and RNA single stranded?
    Single stranded definitely, ribose sugar not sure since it said how would the diagram change so you might not be able to see a difference in the sugar, i put the change of the base T to U but you will probably get the marks 100% 1/2 and probably 2/2
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    (Original post by MedMed12)
    the the RNA different to DNA could I say ribose sugar and RNA single stranded?
    Ribose would still appear the same on the diagram since they are still both hexose :/ but yeah definitely the single stranded
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    (Original post by daisystones)
    Please someone else tell me that they found this quite hard?

    Realised I put plasmodium for the TB question which is of course for Malaria, and I got the ethanol and DEG question wrong how could I have not noticed that it was an enzyme? Grrrrrrrr!

    Hope everyone else thought it went well


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    What was the exact question?
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    Whats the answer for "Why are phagocytes in the tissue fluid?"
    I wrote that they have a multi-lobed nucleus which allows them to squeeze through the gaps in capillary walls.
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    (Original post by GirlWithADream)
    For the squirrel question about why the number of reported cases isnt the same as how many there are, am I right when I said:
    Red squirrels are scared of humans so they hide, therefore people dont see them .
    Also, people could be counting/spotting the same grey squirrels repeatedly.
    I'm sure both would be right. I put that the grey squirrels were larger so there's more chance of seeing them, and they spend more time on the ground, which was given in the passage~
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    (Original post by GirlWithADream)
    For the squirrel question about why the number of reported cases isnt the same as how many there are, am I right when I said:
    Red squirrels are scared of humans so they hide, therefore people dont see them .
    Also, people could be counting/spotting the same grey squirrels repeatedly.
    I put those 2
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    (Original post by PreppyNinja)
    Histamine. Apparently it makes the capillaries more leaky and fluid passes into the lymphatic system or something like that. I wrote that. :/
    Thanks! I would've never got that
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    (Original post by GirlWithADream)
    Whats the answer for "Why are phagocytes in the tissue fluid?"
    I wrote that they have a multi-lobed nucleus which allows them to squeeze through the gaps in capillary walls.
    pushed out of capillary high hydrostatic pressure via the small gaps at arteriole end
    unit 1 stuff
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    What would 69/100 be? This is me being a generous marker :P


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    (Original post by ChloeBazingaa)
    What would 69/100 be? This is me being a generous marker :P


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    B - A
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    (Original post by ChloeBazingaa)
    What would 69/100 be? This is me being a generous marker :P


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    B i think
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    For drawing the lines for r1 and r2 I got them in the right position but for r2 I didn't have the lines half as thick, think that would matter?


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    (Original post by mrdw)
    For drawing the lines for r1 and r2 I got them in the right position but for r2 I didn't have the lines half as thick, think that would matter?


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    Nope they just wanted the position
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    I got almost all Same answers as the unofficial mark scheme. But you missed the question how phagocytes enter tissue fluid? I wrote that infected cells release histamine. This chemical makes capillaries more leaky so blood comes out forming tissue fluid and blood carries with it phagocytes.
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    (Original post by ChloeBazingaa)
    What would 69/100 be? This is me being a generous marker :P


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    B - A. In the past papers an A ranged quite a bit, some were mid to high 60's and some were low to mid 70's, so it just depends on how everyone else did in the country
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    (Original post by jollygood)
    I got almost all Same answers as the unofficial mark scheme. But you missed the question how phagocytes enter tissue fluid? I wrote that infected cells release histamine. This chemical makes capillaries more leaky so blood comes out forming tissue fluid and blood carries with it phagocytes.
    Can you post the unofficial mark scheme???
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    (Original post by Mule)
    So here's my interpretation of the paper for anyone who wants to read (maybe TLDR :P)

    Q1
    Name given to sequence of amino acids (1)
    I put primary structure

    Draw the structure of an amino acid (3)
    H2NCRHCOOH (drawn out)

    Why collagen is good for arteries (1)
    I put strong/tough to withstand high blood pressure, but i'm uncertain, flexibility probably would have been better.

    Describe the structure of collagen molecule (6)
    3 coiled polypeptide chains (quarternary structure) to form a rope
    Left hand helix shape
    Glycine is 1 in every 3 amino acids (smallest R group, close packing)
    Hydrogen bonds between polypeptides
    (now I'm not sure the next is right as it says the collagen molecule but I mentioned lysine's and covalent cross links
    I also said insoluble but I'm not sure thats part of structure,

    Q2
    Type of biological molecule (1)
    Enzyme

    Why can it catalyse both (3)
    I talked about enzyme active site specificity complimentary to substrate. Both molecules have similar shapes/bonds, basically same except 2 less Hydrogen and 1 Oxygen in the DHP (or w/e it was called) So ESC forms.

    Why high ethanol concentration decreases toxicity (3)
    I said they both compete for the active site, where ethanol is present it will enter and stop DHP from entering. So less DHP can be broken down in the same amount of time, so toxic products formed slower, so body can remove these before concentration increases too much.

    Q3
    Infective agent of TB (1)
    Mycobacterium tuberculosis

    How its transmitted (2)
    Exhaled droplets of moisture by infected person inhaled by uninfected people, through coughing, sneezing, laughing, talking (I think you could also mention cattle meat for M.Bovis)

    Describe the data between 2000 and 2008 (3)
    I said low income and middle low stay the same (figures)
    Medium upper increases I think it was and upper decreases
    Both years low is highest incidence, upper is lowest incidence]

    Why low income have greater incidence (3)
    More likely to have malnutrition
    Unable to afford vaccines/antibiotics or take antibiotics when needed
    Overcrowding and sleeping as cannot afford to buy separate houses

    Q4.
    Which cells are phagocytes? (1)
    I put just C although apparently B is too but it looks just as similar to a lymphocyte and a monocyte in my opinion so there should hopefully be allowance in the MS.

    Why "secondary"? (1)
    After primary defence breached, part of immune response to antigens

    Why "non-specific"? (1)
    Can attach to any foreign antigens

    What happens after pathogen attaches to phagocyte? (7)
    Engulfed, membrane infolds, phagocytosis, endocytosis
    Phagosome formed
    Lysosomes move towards and fuse with phagosome
    secrete hydrolytic enzymens/lysins
    break down/digest pathogen
    Into soluble products (e.g. amino acids)
    absorbed into cytoplasm
    waste excreted
    macrophages can become APC's

    Q5.

    Calculate SI of Diversity (3)
    I got 0.6 something

    Species richness (1)
    Number of species present in an area

    Species evenness (1)
    Relative numbers of individuals of each species present in an area

    Low SI Index (2)
    Low biodiversity suggests dominated by few species
    If environmental change, habitat cannot adapt, dependence on that species

    Improve accuracy of sampling (2)
    use random sampling, random coordinates generated by calculator
    Repeat at different times of month/year (I was thinking about selecting suitable quadrate size but chose the other)

    Q6.
    There's a 1 mark question here I can't quite remember, something about genetic variation I think (1)

    Why crop yield varies (2)
    I put insecticides used to stop disease spread, resistance to insecticides, use of fertilisers, climate change (temp/rainfall)

    How genetic variation arises (1)
    Mutation (i wondered if you could put sexual reproduction also)

    Selective breeding short term + long term (7)
    I said this is artificial selection
    Select wild varieties with resistance and cross breed
    prevent asexual reproduction
    Select offspring with resistance and highest yield
    Cross breed again
    repeated for many generations - this is all short term
    Then long term - mutations can cause pathogens to change
    Conserve wild plants, botanic gardens, seed banks, potential of alleles to other diseases
    Multiple alleles to provide better protection
    I also mentioned gene marking somewhere

    I have to admit this question threw me a bit though

    Q7.
    define biodiversity (2)
    Variety of life, range of living species, habitats and communities and the ecosystems of which they form a part
    Genetic variation within and between species

    Why conservation methods needed for the specific area (2)
    Important part of food chains
    Tourism, aesthetically pleasing ( I wonder if you could also put gene pool etc.)

    Suggest why people against culling (1)
    I said morally wrong, inhumane to trap and kill just to keep population down

    Why red squirrel population may be higher than counted (2)
    Grey squirrels not intimidated by humans, red hiding, not seen
    red have better camouflage for red trees, not seen (not sure this is right)

    EIA criteria (3) (did not like this one)
    Effect on biodiversity, environmental sensitivity due to noise pollution (wind turbines)
    whether there are any endangered species (e.g. red squirrel)
    Method to reduce impact (e.g. translocation of red squirrels)

    Q8.
    Components of DNA (2)
    Nitrogenous organic base (I put cytosine as well because it was next to G)
    Nucleotide

    Complete gaps (2)
    Polypeptide
    Ribosome

    How RNA would be different to DNA (2)
    RNA would be single stranded
    RNA would have U instead of T

    Why it is "semi-conservative" (2)
    2 DNA molecules produced, each has one old strand and 1 new strand forms by new nucleotides.

    Why complementary base-pairing is important (2)
    identical molecules of DNA are produced
    so exact protein is made
    purine to pyramidine
    Different base would be mutation, different protein

    Draw in the R1 and R2 (2)
    For R1 I did a line between the N15 line and the N14 line
    For R2 I did half a line at the same position as R1 and the other half at N14

    3 precaution in centrifugation (3)
    Same concentration of sugar solution
    Same volume of sugar solution
    Same time for centrifugation

    Q9
    Fill space (5)
    Whatever the genus was
    I think I got order
    I think I got phylum
    Kingdom = Animalia
    Domain = Eukaroyta

    Phylogeny (3)
    Study of evolutionary relationships, involves ancestral trees
    Classification, placing organisms in groups based on similarities (biochem/anatomy)
    Phlyogeny shows how recent is the common ancestor, more recent = more similarities
    therefore organism placed in similar groups
    less time for mutation/variations to arise

    Why water bear was undiscovered (2)
    Too small to be seen
    Microscopes were not available
    Also talked about speciation because it did say
    why were they not discovered "before 300 years" I think.

    Anyway, these are may answers, they may not necessarily be correct, just for people to make comparisons.

    still 10 marks to be found? total you have in markscheme 90 so some questions missed but good work!
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    Think i got about 77/100, praying for the A!


    In January I got 77UMS, so I think I was able to drop a few marks!
 
 
 
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