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AQA BIOL2 Biology Unit 2 Exam - 26th May 2011 watch

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    pleeeeeeease can someone explain to me tissue fluid?? I dont get it
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    (Original post by f.chowdhury)
    pleeeeeeease can someone explain to me tissue fluid?? I dont get it
    I'll do my best

    There is high hydrostatic pressure at the arteriole end
    So soluble substances are forced out
    The large proteins remain
    The water potential at the arteriole end is lowered [as all the water has been forced out]
    Water returns by osmosis

    That's one thing I don't understand is the water potential as it's not clear. The markschemes don't make it clear when they go that "water potential is lowered so water moves back into the venule end by osmosis"?
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    (Original post by f.chowdhury)
    pleeeeeeease can someone explain to me tissue fluid?? I dont get it
    Tissue fluid is basically the liquid part of the blood that drains out of the capillaries into the spaces between cells. It allows important substances to be transferred to the cells and provides cells with a constant environment (constant pH, temperature and water potential).

    At the arteriole end of a capillary there is a higher pressure, called the hydrostatic pressure, which forces fluid out of the capillary and into the spaces between cells. The fluid moves by osmosis down a concentration gradient because there is more water in the capillary than near the cells. At the venous end of the capillary there is a greater concentration of plasma proteins (less fluid) in the capillary so there is a negative water potential and the tissue fluid moves from the cells back into the capillaries. Any fluid that isn't reabsorbed is drained into the lymph capillaries
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    (Original post by LifeIsGood)
    That's one thing I don't understand is the water potential as it's not clear. The markschemes don't make it clear when they go that "water potential is lowered so water moves back into the venule end by osmosis"?
    That's because in the venous end there are more plasma proteins than tissue fluid (because the tissue fluid exited at the arteriole end) and this creates a negative water potential (W.P. is lowered) so fluid moves down the conc. gradient from where there is more fluid (between the cells) to where there is less fluid (at the venule end of the capillaries).
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    im hoping for a high A on this paper just to secure my overall A
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    im so bored of revision now! i just want the exam to be now!! any good revision techniques guys? :\
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    (Original post by LifeIsGood)
    I'll do my best

    There is high hydrostatic pressure at the arteriole end
    So soluble substances are forced out
    The large proteins remain
    The water potential at the arteriole end is lowered [as all the water has been forced out]
    Water returns by osmosis

    That's one thing I don't understand is the water potential as it's not clear. The markschemes don't make it clear when they go that "water potential is lowered so water moves back into the venule end by osmosis"?
    Can also return by the lymphatic system too.
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    (Original post by LifeIsGood)
    That's so confusing as it seems you're mixing up Mitosis & Meiosis, I don't understand what you're saying except the first bit. Can you explain please?
    Okay, I'll try again.

    During the cell cycle, the DNA replicates in interphase, so by the time it gets to the stage of Prophase, there is twice as much genetic information as there is in a normal cell. So when the cells divide in mitosis, the chromatids are pulled apart, and one sister chromatid from each chromosome goes into each cell. So essentially, the the mass of DNA at the start of prophase is split between the two daughter cells. The number of chromosomes stays the same though.

    In meiosis 1, the homologous chromosomes are separated, so you've got 23 chromosomes in each of the two cells. But during meiosis 2, they divide in a similar way to mitosis, so the chromatids are separated. So you've got four daughter cells, and the mass of DNA is split between those four.
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    Please can someone help with any of the following?

    -Difficulties in defining a species?

    -Importance of taxonomy?

    -Ethics for antibiotic resistance?

    Thanks!
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    (Original post by LifeIsGood)
    I think so yes as mitosis divides to produce 2 identical cells with the same number of chromosomes
    i dont understand, wouldnt the number of chromosomes have to double at some point to have now two cells with the same number of chromosomes, so when you replicate dna arnt you replicating chromosomes? ahhh confused
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    (Original post by kingsmod1)
    try and answer the Questions right LOL

    :aetsch:
    Haha Shhh i panic!
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    (Original post by jessplease)
    i dont understand, wouldnt the number of chromosomes have to double at some point to have now two cells with the same number of chromosomes, so when you replicate dna arnt you replicating chromosomes? ahhh confused
    Yeah, the DNA replicates during interphase, that's why the chromosomes appear as the 'X' shape. Originally, it's just one 'strand', one chromatid. After replication, you have two sister chromatids, which are then separated during mitosis.
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    (Original post by liviaaa)
    Please can someone help with any of the following?

    -Difficulties in defining a species?

    -Importance of taxonomy?

    -Ethics for antibiotic resistance?

    Thanks!
    A species is a group of organisms that can reproduce together to produce fertile offspring. The difficulty in establishing this could result from species being rare and hard to make mate in isolation, and the ethical implications of interfering with the organism to get the DNA sample or what-not.

    Taxonomy is the classification of organisms into a hierarchy. The hierarchy simply being large groups containing smaller groups with no overlap, and allowing organisms to be classified by their common ancestor and evolutionary relationship(phylogenetic classification), or grouping into groups of similar phenotypes/characteristics and alleles.

    The ethical implications of antibiotic resistance mean that bacteria have gained a selection advantage as a result of their mutated resistance gene, and due to this modern antibiotics may not work on them, and without use of multiple antibiotics can result in strains of bacteria resistant to multiple antiobiotics. This can result in more suffering for patients and animals who are infected with these strains as they cannot be treated as effectively as well as leading them to die in this time.
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    (Original post by oHellno)
    Yeah, the DNA replicates during interphase, that's why the chromosomes appear as the 'X' shape. Originally, it's just one 'strand', one chromatid. After replication, you have two sister chromatids, which are then separated during mitosis.
    During interphase can the DNA be seen as a single chromatid or is it diffused throughout the nucleus as chromatin and thus not visible?
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    (Original post by liviaaa)
    Please can someone help with any of the following?

    -Difficulties in defining a species?

    -Importance of taxonomy?

    -Ethics for antibiotic resistance?

    Thanks!
    -Might be extinct, nocturnal.
    -Because some countries have different names for the same organisms so a scientific name helps to identify what they are talking about.
    -Not sure what you mean? Like testing antibiotics on animals?
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    (Original post by kingsmod1)
    LOOL wat u get the last 3 times

    this is my third time and ive had 2 Ds

    I understand all stuff now and have lots of experience lol
    need A
    I got a d last time >__>. But yeah I'm revising properly now last time I actually forgot I had the exam and didn't revise a single minute.
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    (Original post by oHellno)
    Yeah, the DNA replicates during interphase, that's why the chromosomes appear as the 'X' shape. Originally, it's just one 'strand', one chromatid. After replication, you have two sister chromatids, which are then separated during mitosis.
    oh okay, thanks! so the number of chromosomes doesn't change unless its a haploid cell?
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    (Original post by ewoo3148)
    im so bored of revision now! i just want the exam to be now!! any good revision techniques guys? :\
    so am I, I have lost all my motivation today, bored is the only way to describe it. god knows what I'll be like tomorrow night after stats and biology, knowing that I have a chemistry exam the next day too :| i wish they were a bit more spread out
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    (Original post by oHellno)
    Yeah, the DNA replicates during interphase, that's why the chromosomes appear as the 'X' shape. Originally, it's just one 'strand', one chromatid. After replication, you have two sister chromatids, which are then separated during mitosis.
    Thank you, thank you! I understand it a lot more now
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    I'm not sure about the structures of cellulose and starch. Could someone please explain?

    I know that cellulose is made up of beta glucose and starch is made up of alpha glucose. Cellulose has many Hydrogen bonds between its chains for strength and it forms criss-crossing micro fibrils (also for strength). Starch is spiral-shaped to be compact so it takes up less space, and it is branched so that it can be readily hydrolyzed.

    Is there anything else I need to know?
 
 
 
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