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AQA BIOL5 Biology Unit 5 Exam - 22nd June 2011 watch

  • View Poll Results: Are you resitting this unit?
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    (Original post by jbrown42)
    Do you want all the different titles there have been? Or the actual mark schemes because I have the titles, and different things to write about for each one, but not easy to transfer onto here.
    Anything really as I'm really struggling with knowing what to put in the essays, so would you mind sending my the titles you have and the different things to put in each of them. Would it be easier if i just gave you my email?

    Thank you
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    (Original post by EffieFlowers)
    I have a question regarding control of the menstrual cycle... I'd really appreciate an answer!

    Ok, so in terms of positive feedback my book states this:

    Oestrogen stimulates the pituitary to release LH (when in high concentraion, which i fully understand)

    LH stimulates the ovary to release more oestrogen (???)

    Oestrogen further stimulates the release of LH and so on

    I do not understand how LH stimulates the ovary to release more oestrogen? Before reading this, all I was aware of was that LH stimulates the formation of the corpus leutum which releases progesterone. I did not know that LH simulates the release of oestrogen? I know that oestrogen stimulates the release of LH but not the other way around.

    Eep, help, confussiiiooonnn!

    Oestrogen production reaches a peak which induces a positive feedback effect. The hypothalamus releases more GnRH. At this point, the pituitary gland's responsiveness to GnRH increases. This results in a large surge of LH secretion, and a smaller surge of FSH secretion.

    This smaller surge of FSH is what causes the production of oestrogen.

    GnRH stands for gonadotropin releasing hormone. Both FSH and LH are both gonadotrophic hormones.

    I hope this helps.
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    I don't think the menstrual cycle will come up this year, this was a whole question in last years paper.
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    (Original post by User12399)
    We should do a thing where someone asks a question, then they answer it then they ask one as well. Will help us revise?

    Explain the process of the action potential (6 marks)
    Voltage gated sodium channels open, casuing an influx of sodium ions into the axon. If this causes it's charge to reach +40V (The threshold) the membrane is said to be depolarised. This action potenial travels along a neurone by travelling between the nodes of ranvier. Each node is depolarised, like a mexican wave. After depolarisation, potassium gasted channels open. This causes potassium ions to leave the membrane. This repolarises the cell. The oitward diffusion of the potassium ions actually makes the axon more negative than normal, causing hyperpolariation briefly.
    Hyperpolarisation ends, and the sodium-potassium pumps return the cell to it's resting potential.



    Where are cone and rod cells located?
    What is the pigment in each?
    Which cell has the higher visual acuity
    Which cell has the higher light sensitivity
    How are both rod and cone cells connected to bipolar cells.

    Test your eye knowledge
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    (Original post by bethalex)
    Anything really as I'm really struggling with knowing what to put in the essays, so would you mind sending my the titles you have and the different things to put in each of them. Would it be easier if i just gave you my email?

    Thank you
    Yeah, just send me your e-mail in private, and I'll try and get it to you asap
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    (Original post by Vidja)
    Voltage gated sodium channels open, casuing an influx of sodium ions into the axon. If this causes it's charge to reach +40V (The threshold) the membrane is said to be depolarised. This action potenial travels along a neurone by travelling between the nodes of ranvier. Each node is depolarised, like a mexican wave. After depolarisation, potassium gasted channels open. This causes potassium ions to leave the membrane. This repolarises the cell. The oitward diffusion of the potassium ions actually makes the axon more negative than normal, causing hyperpolariation briefly.
    Hyperpolarisation ends, and the sodium-potassium pumps return the cell to it's resting potential.



    Where are cone and rod cells located?
    What is the pigment in each?
    Which cell has the higher visual acuity
    Which cell has the higher light sensitivity
    How are both rod and cone cells connected to bipolar cells.

    Test your eye knowledge
    Cone cells and rod cells are located in the retina which is the inner most layer of the mamalian eye.

    The pigment in rod cells is called rhodopsin.

    The pigment in cone cells is called iodopsin.

    The cone cells has the higher visual acuity and higher light sensitivity.

    Several rod cells share one sensory neurones with a single bi-polar cell whereas in cone cells each cell has its own sensory neurone and bipolar cell.


    (Original post by EffieFlowers)
    I have a question regarding control of the menstrual cycle... I'd really appreciate an answer!

    Ok, so in terms of positive feedback my book states this:

    Oestrogen stimulates the pituitary to release LH (when in high concentraion, which i fully understand)

    LH stimulates the ovary to release more oestrogen (???)

    Oestrogen further stimulates the release of LH and so on

    I do not understand how LH stimulates the ovary to release more oestrogen? Before reading this, all I was aware of was that LH stimulates the formation of the corpus leutum which releases progesterone. I did not know that LH simulates the release of oestrogen? I know that oestrogen stimulates the release of LH but not the other way around.

    Eep, help, confussiiiooonnn!
    Am I wrong to state that LH causes the empty follicle to develop into a structure called the corpus leutem which then secretes progesterone and small amounts of oestrogen until if/when the egg is not fertilised and the corpus leutem degernerates and oestrogen drops until the rebuilding of the uterus lining when the follicle develops as a result of follicle stimulating hormone at the start of the next cycle?
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    (Original post by hiyarearl)

    The cone cells has the higher visual acuity and higher light sensitivity.


    Cones definitely have higher visual acuity but I thought that rod cells were more sensitive, rhodopsin only requires low light intensities to break down whereas iodopsin requires high light intensity, so the rod cells are more sensitive??
    maybe I'm wrong:confused:
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    (Original post by Y.D)
    Cones definitely have higher visual acuity but I thought that rod cells were more sensitive, rhodopsin only requires low light intensities to break down whereas iodopsin requires high light intensity, so the rod cells are more sensitive??
    maybe I'm wrong:confused:
    You're correct, rod cells have higher light sensitivity. There are more of them connecting to the one bipolar cell so there's a higher chance that the threshold is reached (Along with th pigment thing you mentioned).

    Next question since no-one posted one:
    What is siRNA, how is it created, and what is it used for?
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    (Original post by Vidja)
    You're correct, rod cells have higher light sensitivity. There are more of them connecting to the one bipolar cell so there's a higher chance that the threshold is reached (Along with th pigment thing you mentioned).

    Next question since no-one posted one:
    What is siRNA, how is it created, and what is it used for?
    SiRNA is small interfering rna. It is used to control gene expression by halting translation.
    Double stranded rna is cut into fragments by an enzyme called dicer. One strand of each fragment combined with an enzyme to form a complex called RISC. The other strand is discarded.
    The RISC combines with an mRNA with a complementary sequence to the siRNA fragment. The enzyme breaks down the mRNA. This stops the protein the mRNA was coding for being translated.
    SiRNA is useful as it is specific to a section of mRNA, halting the translation of specific genes into proteins.

    Next question: explain how nervous stimulation can cause muscle contraction.
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    i dont understand the refractory period? can someone explain in very simply on how it produces discrete impulses and ensures that they go in one way?
    thankss
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    (Original post by Y.D)
    Cones definitely have higher visual acuity but I thought that rod cells were more sensitive, rhodopsin only requires low light intensities to break down whereas iodopsin requires high light intensity, so the rod cells are more sensitive??
    maybe I'm wrong:confused:
    Oh my bad that's not what I meant, just me rushing to answer, sorry! I was getting confused remembering cone cells require a higher light intensity to reach the threshold value than rod cells and so are only sensitive to high light intensities and for some reason thought "high sensitivity". I wont make that mistake again!

    (Original post by Vidja)
    You're correct, rod cells have higher light sensitivity. There are more of them connecting to the one bipolar cell so there's a higher chance that the threshold is reached (Along with th pigment thing you mentioned).

    Next question since no-one posted one:
    What is siRNA, how is it created, and what is it used for?
    siRNA (small interfering RNA) are double stranded sections of RNA which are involved in the process of breaking down mRNA before its genetic code can be translated into a polypeptide. It occurs as follows; an enzyme cuts large double-stranded RNA molecules into smaller sections called siRNA. One of the two siRNA strands combines with an enzyme and directs the enzyme to a molecule of mRNA as the bases on the siRNA pair up with complimentary bases on a section of mRNA. Once in position the enzyme cuts the mRNA into small sections. The mRNA is no longer capable of translating the genetic code it carries into a polypeptide and therefore the gene is not expressed.

    siRNA can also be used to identify the role of genes in a biological pathway. Some siRNA that blocks a particular gene can be added to cells and the observed effects, or lack of them, can help us determine the role of the blocked genes in the pathway. siRNA may also in the future be used in the treatment of genetic diseases acting to block the genes which cause them.
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    (Original post by cws121)
    i dont understand the refractory period? can someone explain in very simply on how it produces discrete impulses and ensures that they go in one way?
    thankss
    All the refractory period is, is a period after an action potential has been created where the inward movement of sodium ions is prevented as sodium voltage gated channels are closed which just ensures that for a period of time after one impulse (caused by an action potential) there cannot be another action potential created, as influx of sodium ions cannot occur until the sodium voltage gated channel open. This just ensures impulses are separated from one another (are discrete). It ensures they travel in one direction as action potentials can only be propagated in a region that can undergo an influx of sodium ions/an action potential can occur. It cannot be propagated in a region that is refractory.

    I hope that made a bit more sense?
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    (Original post by parallal)
    Yeah, my class had to do it in "exam conditions" last week. I got a low C....
    but I have studied a whole lot more since then.
    I'm really confused/vehemently in disagreement with the answer to one of the questions on there do you think you could ask your teacher it for me? It's the last one on the uptake of IAA by fungus.
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    I hate the menstrual cycle bits, Im refusing to stare at it because it wont stick!!!!!!!!!!!!!!!!!!!!!!!!!!! ! I know it makes an 8 I just have to remember what goes where. Anyone have anytips?
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    (Original post by Destroyviruses)
    I hate the menstrual cycle bits, Im refusing to stare at it because it wont stick!!!!!!!!!!!!!!!!!!!!!!!!!!! ! I know it makes an 8 I just have to remember what goes where. Anyone have anytips?
    dont worry about it too much, it came up last year, so doubt it will come up straight in the next paper, its a new spec so they will try to get new questions.
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    (Original post by User12399)
    dont worry about it too much, it came up last year, so doubt it will come up straight in the next paper, its a new spec so they will try to get new questions.
    okay but im doing last years paper for mock and I want to get a good mark in it so i feel confident.
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    (Original post by Destroyviruses)
    I hate the menstrual cycle bits, Im refusing to stare at it because it wont stick!!!!!!!!!!!!!!!!!!!!!!!!!!! ! I know it makes an 8 I just have to remember what goes where. Anyone have anytips?
    I found it quite hard at first.

    Start by learning the function of each of the hormones properly and then just keep going thought the actual process when you can remember what everything is doing. It will be useful to draw diagrams and imagine it happening from start to finish and then it's just a case of practice. How much more stuff do you have to look at out of interest?
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    I think this exam will really test us on genetic sand dna technology, cloning etc. I can also envisage a few twisted hsw questions coming up about the method of cloning and reasons why you do certain things when doing in vivo/vitro.
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    (Original post by Ramin Gorji)
    I think this exam will really test us on genetic sand dna technology, cloning etc. I can also envisage a few twisted hsw questions coming up about the method of cloning and reasons why you do certain things when doing in vivo/vitro.
    Just great.. you've named the topics I have yet to look over! Oh well, still 2 weeks left yet I guess...
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    (Original post by hiyarearl)
    Just great.. you've named the topics I have yet to look over! Oh well, still 2 weeks left yet I guess...
    To be honest im not 100 percent on any of them. There is far too much to learn in this unit. Feels like im studying for two A levels
 
 
 
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