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    (Original post by branny101)
    any idea on the mark scheme? :awesome:

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    6BI02_01_rms_20130307.pdf
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    (Original post by kimmykim1)
    thank you so much thats much easier but i still dont get what "hydrolysed by the digestive enzymes" means
    hydrolysed by the digestive enzymes is another way of saying the sperm head (with acrosome enzymes) react to disintegrate the zona pellucida,
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    Hard Question really can't solve it at all...i didnt understand the ms too ...so any help will be appreciated:
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    crying, can someone explain the top line? why do they both have crosses, I thought cellulose has H bonds in microfibrils?:cry2:

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    (Original post by yarshad)
    crying, can someone explain the top line? why do they both have crosses, I thought cellulose has H bonds in microfibrils?:cry2:

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    its not the microfibrils that are held by hydrogen bonds, its the cellulose chains that are held by hydrogen bonds.

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    (Original post by Daniel Atieh)
    Hard Question really can't solve it at all...i didnt understand the ms too ...so any help will be appreciated:
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    which paper is this question from?

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    (Original post by Daniel Atieh)
    Hard Question really can't solve it at all...i didnt understand the ms too ...so any help will be appreciated:
    Name:  bio2.JPG
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    For part a) it asks you a definition of the frequency of an ALLELE, we know that frequency means the total number and alleles are different versions for the same gene, so the definition of a frequency of an allele in a population should be:

    a) It is the total number of alleles for one gene in a given area.

    For part b) it asks you to explain natural selection in the enviroment and how it leads to adaption, so a suitable answer would be for four marks (give four points):

    b) (1) Environment change due to a selection pressure
    (2) A mutation occurs
    (3) Advantageous allele in that particular environment
    (4) Hence, more likely the advantageous allele will be passed onto the offspring of the plant

    For part c) a simple 2 marker, we know that bacteria are simple cellular organisms, so to react to the environment we know that:

    1) bacteria can mutate much quicker than plants

    Also we know that (from the stem of the question) that bacteria can react faster, so it should be easy to say that

    2) bacteria has a greater selection pressure than plants if it is to react quickly to the environment.

    Hope that answers your question (and hopefully i got this right, P.S what question paper is this and where can i get a hold of the markscheme? )
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    (Original post by Rubyturner94)
    its not the microfibrils that are held by hydrogen bonds, its the cellulose chains that are held by hydrogen bonds.

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    Yup, thats what i was thinking.
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    (Original post by CoolRunner)
    This asks for changes, so what happens to the sperm cell and egg cell. so you just describe the steps during fertilisation. Its 3 marks so three points are required:

    I would write (well, i haven't looked in the markscheme) something along the lines on:

    1) The sperm cell penetrates through the zona pellucida layer and is hydrolysed by the digestive enzymes secreted from the sperm head.
    2) After penetration, the zona pellucida then reforms/hardens after a sperm has entered to prevent polyspermy (multiple sperms)
    3) Therefore, the process of meiosis is completed.



    The nucleus of a cell is responsible for cellular activity including cell division. Blood cells don't divide, they are produced by other cells within bone marrow.
    aw thanks so much!
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    (Original post by CoolRunner)
    For part a) it asks you a definition of the frequency of an ALLELE, we know that frequency means the total number and alleles are different versions for the same gene, so the definition of a frequency of an allele in a population should be:

    a) It is the total number of alleles for one gene in a given area.

    For part b) it asks you to explain natural selection in the enviroment and how it leads to adaption, so a suitable answer would be for four marks (give four points):

    b) (1) Environment change due to a selection pressure
    (2) A mutation occurs
    (3) Advantageous allele in that particular environment
    (4) Hence, more likely the advantageous allele will be passed onto the offspring of the plant

    For part c) a simple 2 marker, we know that bacteria are simple cellular organisms, so to react to the environment we know that:

    1) bacteria can mutate much quicker than plants

    Also we know that (from the stem of the question) that bacteria can react faster, so it should be easy to say that

    2) bacteria has a greater selection pressure than plants if it is to react quickly to the environment.

    Hope that answers your question (and hopefully i got this right, P.S what question paper is this and where can i get a hold of the markscheme? )
    Well but the things i didnt understand is part b ...maybe coz i dunno what selection pressure is...so tell me please...
    ok i ll post the document and markscheme after a while..i ll arrange it first
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    Is someone able to explain to me in the easiest way gametogenesis in plants
    and Meiosis also
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    Ahhh man! Your link is broken dude, any chance of a re-upload ? =3

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    (Original post by Branny101)
    Ahhh man! Your link is broken dude, any chance of a re-upload ? =3

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    it worked for me, but here it is again
    Attached Images
  1. File Type: pdf 6BI02_01_rms_20130307.pdf (141.8 KB, 48 views)
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    (Original post by mynameisntbobk)
    it worked for me, but here it is again
    Worked this time, thanks.

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    CoolRunner also please gv me ur fb/twitter/email so tht i can send u loads of questions with answers as a document format!
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    (Original post by Daniel Atieh)
    Well but the things i didnt understand is part b ...maybe coz i dunno what selection pressure is...so tell me please...
    ok i ll post the document and markscheme after a while..i ll arrange it first
    selection pressure is an event or condition that requires a 'useful/advantageous' gene to be passed on for survival such as extreme change in conditions, selectron pressure for a particular gene increases, therefore, said gene is passed on more frequently

    (Original post by Rickrossmmg)
    Is someone able to explain to me in the easiest way gametogenesis in plants
    and Meiosis also
    pasically, pollen lands on stigma, then the pollen undergoes mitosis forming 2 nuclei, a pollen tube nucleus and a generative nucleus. The pollen tube nucleus (I'll refer to as ptn) is responsible for digesting its way down the style of the plant and attaches to and disintegrates at the ovary. The generative nucleus on its travel through the style undergoes another mitotic division, there are now 2 nuclei. When they reach the ovary, they enter the ovule and one fertilises the egg nucleus forming a zygoe (a diploid structure (2n number of chromosomes) and the other fertialises a pair of polar nuclei which forms the endosperm (a triploid structure (3n chromosome number))


    http://www.youtube.com/watch?v=GK3eHNu9zsA this is quite good for getting your head around meiosis although I'd say it's not as accurate as it could be
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    (Original post by mynameisntbobk)
    selection pressure is an event or condition that requires a 'useful/advantageous' gene to be passed on for survival such as extreme change in conditions, selectron pressure for a particular gene increases, therefore, said gene is passed on more frequently


    pasically, pollen lands on stigma, then the pollen undergoes mitosis forming 2 nuclei, a pollen tube nucleus and a generative nucleus. The pollen tube nucleus (I'll refer to as ptn) is responsible for digesting its way down the style of the plant and attaches to and disintegrates at the ovary. The generative nucleus on its travel through the style undergoes another mitotic division, there are now 2 nuclei. When they reach the ovary, they enter the ovule and one fertilises the egg nucleus forming a zygoe (a diploid structure (2n number of chromosomes) and the other fertialises a pair of polar nuclei which forms the endosperm (a triploid structure (3n chromosome number))

    http://www.youtube.com/watch?v=GK3eHNu9zsA this is quite good for getting your head around meiosis although I'd say it's not as accurate as it could be
    Alright thanks that was really helpful. You seem to know your stuff! Another thing is all this natural selection business
    Please explain it simpler words
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    (Original post by Rickrossmmg)
    Alright thanks that was really helpful. You seem to know your stuff! Another thing is all this natural selection business
    Please explain it simpler words
    basically, natural selection doesn't just occur on it's own, something has to cause it. That something would be something like an extreme change in conditions of an environment, this means selection pressure is increased, because you won't be able to survive as a species if you don't have the right adaptations, so a mutation occurs, where an advantageous gene is now present and passed on to offsprings. This advantageous gene would be useful for the species to adapt to the change in conditions and for them to breed. The increse in frequency of this gene in the population increases a species chance of survuval, whereas species who aren't adapted won't, hence the term natural selection (or survival of the fittest if it helps you remember it more easily)
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    hey guys can some one explain me the steps for natural selection including the mutation and variation , its repeated alot in pastpapers but i want the steps so i can memorize them and use them , the mark scheme is quite confusing
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    (Original post by kimmykim1)
    hey guys can some one explain me the steps for natural selection including the mutation and variation , its repeated alot in pastpapers but i want the steps so i can memorize them and use them , the mark scheme is quite confusing
    These are the points from the mark scheme:

    1) Idea of selection pressure/change in environment.

    2) Reference to competition/predation.

    3) Mutation (in context).

    4) idea of advantageous allele.

    * What this means is that a change in the environment ( extreme temperature changes etc.)/ or competition (giraffes with longer necks have a better chance of reaching high leafs on a tree, than giraffes with shorter necks)/ or predation (a new predator is introduced to the environment or that there is an increase in a certain predator - more foxes than rabbits) will make that organism have to adapt to the new change. That is caused by a mutation, where an advantageous allele is produced, this allele contains the change(s) that the organism needs to adapt.

    5) Idea that individuals with advantageous {alleles/characteristics} survive and breed.

    6) idea of (advantageous) {allele/mutation} being passed on (to future generations);

    7) idea of more individuals with this adaptation in the population/increased frequency of advantageous alleles in the population.

    * This means that organisms with this advantageous allele will have an advantage over the organisms that don't have the allele. This is natural selection at its finest where the organisms at a disadvantage - without the special allele - will die out while the ones with the allele will survive to reproduce. For the last point, its hinting towards as the generations progress there will be more organisms with the advantageous allele - as more will reproduce - and less organisms with the original genetic makeup as they will have died out.
 
 
 
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