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AQA AS Biology Unit 1 Unofficial Mark Scheme

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    Hey everyone. Hope you did well on your tests.

    As I haven't seen one being made, I've made a start to one and will add more answers when more people contribute to it. This is obviously unofficial, so the real mark scheme could be pretty different. a ; denotes a different point for each mark.

    1)

    a) Golgi Appartus (1 mark)

    b) Nucleus or Nuclear envelope or Nucleolus; lysomomes; Mitochondria;ER
    (2 points for 2 marks)

    c) What's the function of the mitochondria?
    Produce ATP (for energy)

    d) Resolution is highest/greatest; due to shorter wavelength of electrons; can see detailed structures; amoeba are thin so TEM works (2 marks)

    2)

    Describe investigation A
    a) 2 drinks decrease the risk of heart disease; then increase it (as you drink more) (2 marks)
    b) Why does the 40-50 age group improve the investigation? Increases reliability because alcohol affects different age groups in different ways (metabolism, etc). (1 mark)
    c) Evaluate the claim 'Alcohol is good for you' (3 marks)

    Yes - in low consumption;
    No - correlation does not mean causation;
    may be another factor involved;
    drinking more than 2/3 increases the risk of heart disease;
    didn't specify what alcohols were so can't be sure on the quantity;

    3) a) Describe what causes the diaphragm to change shape
    (lungs changed shape) diaphragm contracts and flattens;

    b) During these two phases, air moves into the lungs. Describe how the diaphragm allows this. (3 marks)
    Diaphagm causes inspiration by contracting;
    reducing pressure in the lungs;
    air pressure outside greater causing it to flow into the lungs;

    c) Diffusion through concentration graident; (2 marks)
    through thin epithelium of alveoli;
    then through thin endothelium/epithelium of capillary wall;

    4) a) What is a pathogen? A micro-organism that causes disease. (1 mark)
    b) Phagocytes may destroy bacteria. Explain how. (4 marks)

    Phagocytes attracted by chemicals/recognise the antigens;
    Engulf/ingest bacteria;
    Remain in vacuole/vesicles/phagosome;
    Lyosomoes release (hydrolytic) enzymes/fused with vacuoles;
    Pathogen digested/hydrolysed/broken down;

    c) Why does the antibody only target the specific antigen? (2? marks)
    Specific primary structure/amino acid sequence;
    Specific tertiary structure;
    Determines binding sites;
    Complementary to specific antigens;


    5) (Cyanide)

    a) Describe what the graph shows. Slows it down up to (a certain point); then, sodium uptake is halted completely; (2 marks)
    b) 0.2. The y-axis said concentration remaining, so you had to do 10 - 4 which is 6. Then divide that by 30 to get 0.2
    c) Cyanide affects respiration. How did the cyanide affect the sodium uptake? (Controversial too - I looked it up on Wikipedia and apparently it binds to cytochrome c in the mitochondria) (2? marks)

    Acts as a competitive inhibitor;
    Prevents mitochondria producing ATP for energy;
    Energy needed in active transport/sodium-potassium pump/co-transport;
    To remove sodium and maintain low concentration;

    OR

    Less respiration happening;
    Therefore glucose not being used up as quickly;
    Therefore rate of uptake of glucose slower;
    Glucose moves into cell by co-transport with sodium ions;
    Therefore slower rate of glucose absorption means a slower rate of sodium ion absorption.

    6) Starch/amylase question
    a) Describe the test for reducing sugars (3 marks)
    Heat;
    with Benedicts reagent/solution;
    Brick red precipitate will form;

    b) Why did solution B contain more than Solution A? Quite controversial. (3 marks)
    enzyme breaks down starch into maltose
    reducing water potential in tube;
    water moves in via osmosis;


    c) The student said that a pH of 8 was the optimum temperature. Is this right? (1 mark)

    Didn't test intermediate values (2-8);
    Didn't test values above 8;

    7) a) Hydrolysis (1 mark)
    b) Proteins too large; carrier proteins are specific; carrier proteins may be damaged;
    The proteins in membrane are selective; The conc of amino acids in cell is greater than conc of amino acids outside cell; facilitated diffusion involves that involves movement of
    large molecules DOWN a conc gradient. Hence why the dipeptide cannot diffuse through. (3 marks)
    c) Villi become damaged; reduced surface area; less diffusion;
    membrane bound enzymes; reduced breakdown of proteins; less absorption (Once only for less absorption) (3 marks)

    d) Why does the gluten stimulate an immune response? (Some lines from the text) + sees it as non-self (1 mark)

    e) Factors to consider: Side effects; Cost; Injection/Oral; Overall effectiveness; Amount needed; Age; Gender (2 marks)


    8) a) How does the heart co-ordinate contraction of the atria and ventricles? (5 marks)

    SAN sends out electrical activity/wave of impulses;
    Stimulates contraction of atria/initiates heart beat/acts as pacemaker;
    AVN delays (electrical impulses);
    Allowing atria to fill before ventricles contract/ventricles to fill before
    contract;
    AVN sends of wave of electrical activity down Bundle of His/Purkyne fibres;
    Causing ventricles to contract (from base up) / ventricular systole;

    b) How does a diet increase the risk of heart disease? (5 marks)

    High consumption of fat/cholestrol accumulate in artery wall/ under lining / endothelium of artery;
    Atheroma;
    Can cause blood clots/thrombus
    May break off;
    and get lodged in the coronary artery;
    Reduces blood supply;
    (so) reduces oxygen supply;
    Heart muscle can't respire without oxygen and so dies;
    Salt/ions;
    can causes high blood pressures;


    Why are people negging :L mad because you got things totally different to this?
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    ahh great thread ! ,, hmm 2a describe the heart disease graph ,investigation A? i put that for maximum of 2 drinks the risk of heart disease decreases, however after 2 drinks the risk of disease increase by a higher rate after every 1 more drink.
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    There was the usual 'what is a pathogen' - a microorganism that causes disease. Loads of questions have been written about in the other thread but I don't remember their numbers at all, sorry.
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    I think the answer to 7b was carrier proteins/protein channels destroyed, cell-surface membrane damaged, (can't figure out whether microvilli would be included in the answer to that too)
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    mediterrenean OMGGGG I WROTE THAT TOO !!! i thought i got that wrong but WOOW yayyy, and exactly i mean it said 'look at lines 4-5' but i still included the villi bits anyway !
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    (Original post by MediterraneanX)
    I think the answer to 7b was carrier proteins/protein channels destroyed, cell-surface membrane damaged, (can't figure out whether microvilli would be included in the answer to that too)
    the answer is on january 2010 4b
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    I think 7b asked something about why peptides cannot diffuse through the membrane using facilitated diffusion.
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    (Original post by adnan12345)
    mediterrenean OMGGGG I WROTE THAT TOO !!! i thought i got that wrong but WOOW yayyy, and exactly i mean it said 'look at lines 4-5' but i still included the villi bits anyway !

    I wrote that too Hi5
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    Part c) on question 2 asked to evaluate the newspaper claim of "Alcohol is good for you".

    For: Between 1-3 drinks of alcohol is shown to decrease the risk of heart disease by the diagram

    Against: States "good for you" - not to do with heart disease as shown by the diagram

    Correlation does not show causation - could be due to another factor

    The increase of intake after 3 drinks shows to increase the risk of heart disease

    I think :3
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    somewhere in question 2 "drinking alcohol is good for you." evaluate this claim. it was something like that anyway and it was 3marks i think.

    -ddoesn't take into account other problems alcohol can cause would be one mark i thinks
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    Did ANYONE write down anything to do with co-transport for the cyanide question?
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    For 7c you could also write that the microvilli contain membrane bound enzymes -> reduced breakdown of proteins -> reduced absorption

    damaged membrane -> less carrier proteins -> lower rate of diffusion -> less absorption
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    2b: i dont think lysosomes are an answer

    7c microvilli are on it, reduced surface area so slow. and transport proteins lost slowing diffusion and transport.
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    The one about why it couldnt uptake peptides by facilitated diffusion.
    I put they are too large and also, facilitated diffusuion is from a high to low concentration, but the cells had peptides in them, so the concentration gradient was reversed..?? :/

    The cyanide question was just plain evil

    Also the diaphrapm quesstion, first bit what describe what between P and Q brings about change of shape
    and the second part was about how the changes were brought about (both vague questions) so i put almost identical answers for both.

    Then there was describe how air in alveoli goes into blood in capillaries..?
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    was the answer to one of the questions 'hydrolysis' because i think i put 'condensation' OMG:confused:
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    (Original post by Monster Mnch)
    I think 7b asked something about why peptides cannot diffuse through the membrane using facilitated diffusion.
    7b is because they are too big i think.
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    (Original post by Scienceisgood)
    Did ANYONE write down anything to do with co-transport for the cyanide question?
    Yes, something to do with sodium stimulates the co-transport of glucose, glucose required for respiration etc.
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    (Original post by Chris..)
    somewhere in question 2 "drinking alcohol is good for you." evaluate this claim. it was something like that anyway and it was 3marks i think.

    -ddoesn't take into account other problems alcohol can cause would be one mark i thinks
    I said the following;

    1. Alcohol does decrease your chances of getting heart disease after drinking 2 drinks.
    2. After this, it rises
    3. Alcohol in excess can cause liver damage or lower your reaction speed.

    How many do you think I will get.

    I also mentioned that that the other 2 experiments used 6 drinks and A only used 5.=l
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    lungs changed shape, because intercoastals and diaphagm contract

    diaphagm causes inspiration by contracting, reducing pressure in the lungs, air pressure outside greater causing it to flow into the lungs.
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    can't remember the questions but it asked
    why the tube with ph8 was higher up than the tube with ph2
    and the questions before that was asking about how to test for reducing sugars

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