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WJEC BY4 January 25 Unofficial Mark scheme

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    I thought it'd be useful to provide an unofficial mark scheme. Most of these will initially be off my memory so I don't remember the question numbers, sorry.

    First question: (Labelling of the neurone)
    From top to bottom:

    i)Dendrite
    Axon
    Node of Ranvier
    Synaptic Bulb

    ii) Two types of effectors
    Muscle
    Gland

    iii) Where would region X be found in a spinal cord?
    Ganglion

    iv) Which root would Y be found?
    Ventral(As it's a motor neurone)

    Kidney micrograph question:
    There was definately a glomerulus and bowman's capsule present, not sure about the third one.

    When asked which section of the kidney it is from, it's the cortex.

    In micrograph B, those seen are loop of henle (ascending and descending) and collecting duct

    Nitrogen cycle "filling in the gaps"


    Pseudomonas decomposes the nitrates from plants into ammonia
    Nitrosomonas convert ammonia into nitrites
    Nitrobacter decompose the waste products of this bacteria to nitrates
    Rhizobium found in root nodules
    Azotobacter found free living in soil

    Bacteria graph:
    Why is the population growth less in lactate than in glucose?
    Possibly because an enzyme is required to split lactate into its' monosaccharides
    Possibly because it has less Carbons

    Describe the graph of Q
    Possible answers:
    General increase, from 0-30 minutes it enters lag phase, synthesising of enzymes
    30-210 enters log phase where it generally increases(population)
    The dip could be due to intraspecific competition, or where nutrients ran out and were re-added
    Enters stationary phase after 210 minutes, death rate = birth rate

    Labelling of ATP:
    What is the name of the reaction produces ATP?
    Phosphorylation

    What is the name of the pentose sugar?
    Ribose

    What is the name of the base?
    Adenine

    Describe how energy is released from ATP

    High energy phosphate bonds hydrolyses. Catalysed by the enzyme ATPase. Releases 30 kJmol-1 of energy

    Photosynthetic alga question:
    Describe and explain the distribution of bacteria

    The bacteria are found mainly in blue and red wavelength sections. Photosynthesis releases oxygen and takes place best with red and blue wavelengths of light. In these sections more oxygen will be present and so the oxygen seeking bacteria will be most likely to stay near these areas.

    What would happen if the prism was removed?
    The bacteria would align in the centre point (Where the light would shine)

    Describe the process by which oxygen is released by the alga?
    Non cyclic photophosphorylation. PSI loses 2 electrons which are replaced by 2 electrons from PSII. Water undergoes photolysis which products are oxygen, electrons and hydrogen. The electrons and hydrogen are used to reduce NADP and the oxygen is evolved - thus producing oxygen. (Worth 6 marks so more points would be needed)

    Essay questions:

    a) (I didn't do this so don't remember it)

    b) i) Describe the important of the cell membrane in nerve transmission:
    Explain about there being pumps and channels in the membrane and when an impulse arrives the Na+ channels open and the Na+ ions rush in by diffusion, depolarising the membrane. Then K+ channels open and this causes repolarisation. There is a refactory period where the channels and pumps can not work which ensures unidirectionality. (Requires more points as it was 7 marks)

    ii) And in nerve transmission across a synapse:

    Describe how the impulse causes Ca2+ to move into the synaptic bulb and this causes the synaptic vesicles to fuse with the presynaptic membrane, secreting their neurotransmitter by exocytosis. This diffuses across the synaptic cleft and the protein receptors in the post synaptic membrane detect them, which causes the Na+ channels in the post synaptic neurone to open, and Na+ diffuses in, causing depolarisation.


    If you know any more questions/want to know answers let me know and I'll try and remember what I put.

    P.S. These are what I wrote and asked my teacher and so they may or may not be correct
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    Nitrogen cycle "filling in the gaps"

    Pseudomonas decomposes the nitrates from plants into ammonia


    Pseudomonas are denitrifying bacteria and so convert ammonia/ammonium ions + nitrates back to nitrogen
    the opposite reaction of nitrification.
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    (Original post by Rhodz999)
    Nitrogen cycle "filling in the gaps"

    Pseudomonas decomposes the nitrates from plants into ammonia


    Pseudomonas are denitrifying bacteria and so convert ammonia/ammonium ions + nitrates back to nitrogen
    the opposite reaction of nitrification.
    yeah you're right. for that blank i put 'decomposing bacteria and fungi' because we aren't actually given a name in the guide or anywhere else.
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    (Original post by WelshLewis!)
    yeah you're right. for that blank i put 'decomposing bacteria and fungi' because we aren't actually given a name in the guide or anywhere else.
    Ah right. In my WJEC guide (The black/green one) it had psuedomonas in it
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    Ah my bad guys I see what you mean now! I said putrefying bacteria I think.
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    For question one, wouldn't structure X be found in the grey matter, as it was a motor neurone, and it's the cell bodies of sensory neurones that are found in the dorsal root ganglia?
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    The bit labelled X was grey matter and motor neurones are found in the ventral root
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    (Original post by WelshLewis!)
    yeah you're right. for that blank i put 'decomposing bacteria and fungi' because we aren't actually given a name in the guide or anywhere else.
    I pit putrefaction bacteria, how do you know?
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    (Original post by lee_vassallo)
    The bit labelled X was grey matter and motor neurones are found in the ventral root
    Are you certain?
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    (Original post by Kharman11)
    I pit putrefaction bacteria, how do you know?
    How do I know what? Putrefaction is also correct.
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    (Original post by AlexBamsey)
    Ah my bad guys I see what you mean now! I said putrefying bacteria I think.
    Do you know when we normally get these results? I didn't sit any in January last year.
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    Synaptic bulb? Surely it was axon terminals.
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    (Original post by XO*)
    Synaptic bulb? Surely it was axon terminals.
    This is what I was told too.
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    It was putrefaction not dentrification. So the answer was saprobiotic bacteria.

    Pretty sure it was dorsal root.
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    (Original post by AlexBamsey)
    I thought it'd be useful to provide an unofficial mark scheme. Most of these will initially be off my memory so I don't remember the question numbers, sorry.


    P.S. These are what I wrote and asked my teacher and so they may or may not be correct
    In that case why title this as a mark scheme?
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    Axon terminal/ Synaptic Knob/ Synaptic Terminal are normally all acceptable. Never heard of Synaptic Bulb though.
    And my teacher said it was the ventral root.
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    (Original post by XO*)
    Synaptic bulb? Surely it was axon terminals.
    This is what I put also
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    (Original post by XO*)
    It was putrefaction not dentrification. So the answer was saprobiotic bacteria.

    Pretty sure it was dorsal root.
    I'm guessing decomposers would be alright as well? Had to decide between putrefaction and decomposers, so put the substance that does it as the rest of the passage was mostly talking about the substances/enzymes. I am guessing they would accept but putrefaction and decomposers though, as it was not made clear whether to put the name of the process, or what actually does it?
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    It is putrefaction, denitrification is wrong because it's a different process, and it was grey matter, not ganglian, i think x on the kidney picture was an efferent arteriole
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    (Original post by WelshLewis!)
    Do you know when we normally get these results? I didn't sit any in January last year.
    Mid to late march

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Updated: January 26, 2012
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