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A level Biology: Post your doubts here!

Discussion in 'International A And AS Level' started by XPFMember, Sep 29, 2011.

  1. XPFMember

    XPFMember XPC Moderator Staff Member

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    Hi everyone, assalamoalaikum!! :)

    To get things organized in a better way, I am making this thread. As othewise, some queries remain unanswered!

    So post your A LEVEL BIOLOGY doubts in this thread. InshaAllah those who can , will help me and you all. :D ;)

    Will try to update this soon, by adding links to some Biology Notes & Links around the forum.

    Thanks!
    Jazak Allah Khair!

    BIOLOGY LINKS & NOTES :


    B!0l0gy $l!de$ & N0te$... :) - by workinghard

    Biology Practical notes!! - by libra94

    http://www.biologymad.com

    http://www.biologyinnovation.co.uk

    Action Potential - Notes
     
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  3. XPFMember

    XPFMember XPC Moderator Staff Member

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    Re: Biology Doubt: Nervous System!

    Assalamoalaikum!

    Can someone please explain, what's refractory period? I am confused about it! =/
     
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  4. AAestar

    AAestar

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    Re: Stuck in Biology?? Post your doubts here!!

    Following the passage of one Action Potential, there is a time delay before the next one can pass. This time delay is known as refractory period and it lasts for a few milliseconds. During this time, the sodium channels in the membrane are closed, preventing the inward movement of Sodium ions. This is known as the absolute refractory period. Another impulse cannot be conducted no matter how large the stimulus is.
     
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  5. hassam

    hassam

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    Re: Stuck in Biology?? Post your doubts here!!

    WELL SOME BODY CLEAR ME....THAT IN LOOP OF HENLE WATER IS GIVEN OUT TO PERITUBULAR CAPILLARIES OR TISSUE OF MEDULLA?
     
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  6. mrpaudel

    mrpaudel

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    Re: Stuck in Biology?? Post your doubts here!!

    Draw a plan diagram...label vascular bundle and palisade layer..!!
     

    Attached Files:

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  7. XPFMember

    XPFMember XPC Moderator Staff Member

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    Re: Stuck in Biology?? Post your doubts here!!

    Any other definition?!
     
  8. mrpaudel

    mrpaudel

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    Re: Stuck in Biology?? Post your doubts here!!

    and..other one m confused bout is....!! When enzymes are immobilized, what will happen?? i mean..they are all covered by those inert materials..or what else?? any if they are all covered..how do they help in a reaction?
     
  9. AAestar

    AAestar

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    Re: Stuck in Biology?? Post your doubts here!!

    When an action potential has just occurred at a section of the axon, there is a short period of time when a second action potential can be generated at the same point. This is called the refractory period.

    What about this one?
     
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  10. AAestar

    AAestar

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    Re: Stuck in Biology?? Post your doubts here!!

    Immobilized enzymes can be recovered easily from a reaction and be used over and over again. The reactant products are not contaminated by the enzyme because the enzyme are held in matrix.
     
  11. mrpaudel

    mrpaudel

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    Re: Stuck in Biology?? Post your doubts here!!

    When...substrate molecules is kept with the immobilized enzymes, the substrate molecules diffused into the droplets to reach the enzymes and react ??? this is the way how immobilized enzymes work?
     
  12. anillatoo

    anillatoo

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    Re: Stuck in Biology?? Post your doubts here!!

    How does anyone remember photosynthesis n respiration processes? It's pretty complicated, too many details to memorise!
     
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  13. aquariangurl

    aquariangurl

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    Re: Stuck in Biology?? Post your doubts here!!

    ^Flowcharts is the best solution to that.
    Or seriously, watch the videos by www.khanacademy.org over & over again.
     
  14. XPFMember

    XPFMember XPC Moderator Staff Member

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    Re: Stuck in Biology?? Post your doubts here!!

    Assalamoalaikum! :)

    Can somebody plz help me with the role of synapses..?!

    I'm giving a bit of info, it'd be good if anybody could help me with the rest! :unknown: :)

    1) Synapses ensure one-way transmission, as the synaptic vesicles containing the neurotransmitter substances are only present in the presynaptic neurone, and the receptors for these neurotransmitters are only present in the post synaptic membrane.

    2) They are involved in memory and learning. This is due to the formation of new synapses which link the neurones that carry information along particular pathways.

    Let me know if there's any mistake in the second point. And I'd like some further points which are listed in the mark scheme as follows. I didn't understand those points, so I am unable to link them! :oops:

    Below are all the points in the mark scheme
    -ensure one-way transmission
    -receptor only in post synaptic membrane
    -vesicles only in presynaptic neurone
    -adaptation due to overuse of synapse
    -wide range of responses
    -due to inter connection of pathways
    -inhibitory synapses affect other synapses
    -involved in memory/learning
    -due to new synapses being formed
    -summation

    Jazak Allah Khair for all the help!
     
  15. mrpaudel

    mrpaudel

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    Re: Stuck in Biology?? Post your doubts here!!


    As aquariangirl, i also suggest u to watch videos in this site www.khanacademy.org u wil never forget in ur life after u watch those videos couple of times.!!
     
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  16. AAestar

    AAestar

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    Re: Stuck in Biology?? Post your doubts here!!


    Your first and second points are correct. The other role of synapse is that it increase the possible range of actions in response to a stimulus. Synapses allow a wider range of behavior than could be generated in a nervous system in which neurones were directly 'wired up' to each other. They do this by allowing the interconnection of many nerve pathways.

    This is all I can help for the time being. I am not sure about inhibitory synapses and summation.
     
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  17. hassam

    hassam

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    Re: Stuck in Biology?? Post your doubts here!!

    whats the role of VASA RECTA.....and ....is vasa recta the name for blood vessels around loop of henle via peritubular cpillaries for around distal and proximal?
     
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  18. iceman

    iceman

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    Re: Stuck in Biology?? Post your doubts here!!

    What are polar molecules???
     
  19. Nibz

    Nibz XPC Global Moderator Staff Member

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    Re: Stuck in Biology?? Post your doubts here!!

    Molecules having partially positive and partially negative charge.
     
  20. AAestar

    AAestar

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    Re: Stuck in Biology?? Post your doubts here!!

    Yup, Vasa recta is the blood capillary which collects the filtered blood from the afferent arteriole. They play an important role in forming concentrated urine. The useful molecules (salts and water) are reabsorbed from renal tubule into the blood in vasa recta. Vasa recta conveys this blood to the renal venules and then these venules unite together to form renal vein.
     
  21. XPFMember

    XPFMember XPC Moderator Staff Member

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    Re: Stuck in Biology?? Post your doubts here!!

    Assalamoalaikum!

    Please, help me with this question:
    Describe the function of vasa recta.

    Mark scheme points:
    -removing water;
    -from/ reabsorbed by collecting ducts;
    -ref. to maintain water potential gradient (in medulla)

    Jazakumullah Khair.. :)
     
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