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    (Original post by SKK94)
    The main difference is in their function:
    - DNA polymerase: assembles complementary DNA nucleotides along a single DNA strand, resulting in the formation of a double-stranded DNA molecule. This enzyme is involved in DNA replication.
    - RNA polymerase: assembles complementary RNA nucleotides along a single DNA strand, resulting in a molecule of mRNA. This enzyme is involved in transcription
    - Reverse transcriptase: as the name suggests, it does the opposite of transcription. It assembles complementary DNA nucleotides along a molecule of RNA (viral RNA) resulting in a single strand of complementary DNA (cDNA). This enzyme is involved in viral replication in host cells.




    ANGELLLL thank youuuuuuuuuuu.

    okay one more thing...

    difference between sense and antisense strand...

    and how do we know which sampling to go for, random or systematic, i guess i asked this before also, but im not sure.
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    (Original post by Trinitybabe)
    what your definition of gene flow would be? what context / example please?
    Gene flow is the transfer of alleles or genes from one population to another. for example when there is a reproductive isolation (where interbreeding is prevented) between two populations of the same species, there is a restriction of gene flow whereby there are no transfer of genes from one population to another. over time, they can no longer breed together to produce fertile offspring due to the change in phenotype.
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    (Original post by iwantopas19)
    ummm? can u be more specific ?

    gene : sequence of amino acids that codes for a particular protein or function.

    flow: u know the meaning

    basically it means the transfer of genes form one organisms to another through sexual reproduction.

    for example, if a geographical barrier arises between a population of a species, means they cannot interbreed therefor no gene flow between them.
    thanks guys, that helps me a lot. i can t wait to get over and done with unit 4..i feel i m doing the same thing over and over..and still can t get it right..even if i understand the context...i had a terrible E in january and i need a B to get into Uni..i m kind of scared. what s your target for next uni?
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    (Original post by iwantopas19)
    okay I know this sounds so dumb, but seriously can someone please explain me what one earth HSW is? where can I find relavanet infos about HSW which is related to our specification? :dontknow:
    How Science Works. There are HSW sections in the A2 student book (green one) , for each chapter ( I don't know about the SNAB book though )
    Check out page 13 of the biology specification to see how to use them.
    Sorry, I don't think this was very helful
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    i do not understand the difference between homozygosity and heterozygosity, and why is homozygosity caused by inbreeding? could someone pls explain


    one more thing... do we have to remember all methods and procedures from the unit 4 practicals?
    anyone's help is very much appreciated
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    is the exam at am or pm?
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    (Original post by amber109)
    is the exam at am or pm?
    it is at AM.
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    (Original post by bubblegummer)
    i do not understand the difference between homozygosity and heterozygosity, and why is homozygosity caused by inbreeding? could someone pls explain
    I think this is right, somebody correct me if not.
    If a cell is homozygous it has two of the same allele at a locus (a location on your DNA), one from each parent eg a-a
    If a cell is heterozygous is has two different alleles at a locus eg A-a

    The more inbreeding that happens the greater chance there is of keeping those alleles in the family. This can be bad, as -for example- in some cases having two recessive alleles can give you a genetic illness.
    So let's say Mum is A-a and Dad is A-a. There kids can take one of the alleles from each parent.
    They have a boy1 (A-a) and a girl1 (a-a).
    They do the dirty, and the chances of their kids having a-a is greater (as there are more as between them).
    So lets say THEY have a boy2 (a-a) and a girl2 (a-a). Now a-a is the only zygous in this family, and every generation after this will have to genetic illness.

    Sorry was long winded! Hope that answered your question? :rolleyes: I don't even think it comes up in this unit does it?
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    (Original post by PakStar28)
    it is at AM.
    thanks
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    (Original post by Lgambo)
    I think this is right, somebody correct me if not.
    If a cell is homozygous it has two of the same allele at a locus (a location on your DNA), one from each parent eg a-a
    If a cell is heterozygous is has two different alleles at a locus eg A-a

    The more inbreeding that happens the greater chance there is of keeping those alleles in the family. This can be bad, as -for example- in some cases having two recessive alleles can give you a genetic illness.
    So let's say Mum is A-a and Dad is A-a. There kids can take one of the alleles from each parent.
    They have a boy1 (A-a) and a girl1 (a-a).
    They do the dirty, and the chances of their kids having a-a is greater (as there are more as between them).
    So lets say THEY have a boy2 (a-a) and a girl2 (a-a). Now a-a is the only zygous in this family, and every generation after this will have to genetic illness.

    Sorry was long winded! Hope that answered your question? :rolleyes: I don't even think it comes up in this unit does it?
    i can understand them better now. hmm i don't think this is in our spec, but i saw it somewhere in the old past papers. not sure though. thank you so much btw
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    Predictions for the exam tomorrow:
    Photosynthesis
    -Hydrogen stored as a fuel in glucose
    -Photolysis in the L.D. reactions
    -ATP as energy
    -Usage of the L.I. reaction products
    Food chain/habitats etc.
    -Trophic levels
    -NPP/GPP
    -Biotic/abiotic factors in distribution
    -Niche within a habitat
    Carbon etc.
    -Carbon cycle
    -Global warming (cause and effect)
    -The effect of temperature on enzyme activity (kinetics etc.) and the development of organisms
    -Evidence for global warming, and why this might be controversial/not accepted
    -The decomposition of organic material by micro-organisms
    Immune system etc.
    -Antibiotic resistance
    -Bacteria vs. viruses
    -Non-specific immune system
    DNA etc.
    -Protein synthesis
    -The use of exons in producing multiple types of proteins from one gene
    -DNA profiles
    A specific TB/HIV question?

    Anyone else got any guesses?
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    Can someone name all the experiments? Thanks
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    (Original post by Brad0440)
    Predictions for the exam tomorrow:
    Photosynthesis
    -Hydrogen stored as a fuel in glucose
    -Photolysis in the L.D. reactions
    -ATP as energy
    -Usage of the L.I. reaction products
    Food chain/habitats etc.
    -Trophic levels
    -NPP/GPP
    -Biotic/abiotic factors in distribution
    -Niche within a habitat
    Carbon etc.
    -Carbon cycle
    -Global warming (cause and effect)
    -The effect of temperature on enzyme activity (kinetics etc.) and the development of organisms
    -Evidence for global warming, and why this might be controversial/not accepted
    -The decomposition of organic material by micro-organisms
    Immune system etc.
    -Antibiotic resistance
    -Bacteria vs. viruses
    -Non-specific immune system
    DNA etc.
    -Protein synthesis
    -The use of exons in producing multiple types of proteins from one gene
    -DNA profiles
    A specific TB/HIV question?

    Anyone else got any guesses?
    You basically summarised the whole specification ...
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    Also, I don't know how useful this is but I've attached some of my revision posters for this exam...
    Attached Files
  1. File Type: pptx Unit 4 biology revision.pptx (1.11 MB, 216 views)
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    can someone or anyone tell me the difference between definition of species and of reprodcutiive isolationnnnnnnnnnn
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    (Original post by iwantopas19)
    difference between sense and antisense strand...

    and how do we know which sampling to go for, random or systematic, i guess i asked this before also, but im not sure.
    The antisense is the strand used as a template to make the mRNA. ( The RNA nucleotides are complementary to bases on this strand)
    The sense strand is the DNA strand opposite the antisense strand. It is identical to the mRNA that is formed (except thymine is present instead of uracil)
    http://www.google.ae/imgres?q=sense+...6&tx=215&ty=33
    http://www.google.ae/imgres?q=antise...15&tx=24&ty=62

    Systematic sampling is used when you want to find a trend within an area, relating two variables. For example, to find the effect of distance from shore on the number of shrubs. So you will have to place a line transect starting from the shore and up to, say, 200m.
    Now, along this 200m line transect, you can place quadrats at fixed distances and count the number shrubs in each.
    Next, you might a pattern with number of shrubs and distance from shore ( i.e the number of shrubs increases with increasing distance)

    Random sampling may be used when you want to a trend between two different areas. For example, the effect of light intensity on then number of seeds produced by a plant. You have to choose two areas of the same size (but different light intensities, of known values).
    Say one area has low intensity and the other has high intensity. Next, use random sampling within each area to count the number of seeds in each. With this you can see the effect of light intensity on number of seeds produced.

    Sorry this is really long! I hope this helped
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    (Original post by Brad0440)
    Also, I don't know how useful this is but I've attached some of my revision posters for this exam...


    its cute
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    (Original post by iwantopas19)
    can someone or anyone tell me the difference between definition of species and of reprodcutiive isolationnnnnnnnnnn
    HEY
    An organism is defined as being a different species if can't interbreed to produce fertile offspring.
    Reproductive isolation is just that, not being able to produce fertile offspring (due to sex organ differences or mating season differences blalbllalbla)
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    (Original post by iwantopas19)
    can someone or anyone tell me the difference between definition of species and of reprodcutiive isolationnnnnnnnnnn
    A species are a group of individuals that have similar similar characteristics and can breed to produce fertile offspring.

    Reproductive isolation is when individuals of a species cannot breed with each other.
    This may be due to a change in structure of reproductive organs, not allowing for sexual reproduction.
    It could also be because individuals in a population were geographically separated, and with time, developed different reproductive cycles or courtship behaviours that do not let them to breed with each other.
    Reproductive isolation is a way that different species are formed.
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    I was going through the January 2010 paper and i came across a question related to reverse transcriptase?
    I swear this isn't in the specification and i also checked the CGP book and it isn't there.
    I'm worried now? :/
 
 
 
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