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

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    (Original post by cor_fortis)
    acetyl is a molecule not a functional group, it is actually ethanoyl, but Alevel biochemistry dumbs it down a bit.
    My two books say it is broken down into acetate and choline. One is written by the head examiner I think. Wiki says this too...
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    (Original post by l4ith)
    Too low pH increases heart rate so you can remove as much CO2 in the lungs as possible to raise the pH again
    Thanks, got my pH's mixed up, keep doing that :/. Edited the post now
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    (Original post by NRican)
    MRSA highly resistant strains.


    What are 3 key difference between DNA, mRNA and tRNA, excluding size, location, stability.
    DNA is the only one that contains Thymine. All other RNA Uracil instead.
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    (Original post by Phalange)
    My two books say it is broken down into acetate and choline. One is written by the head examiner I think. Wiki says this too...
    Different sources say different things....I hate AQA.
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    sorri guys but i do not understand why they use the sanger method and how that helps locate the bases they are lookin got, i mean if they didnt kno the bases they lookin for so then why are primers complemantary to it

    many thanks!!!! :P
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    Hey, is anyone bothering to learn AS biology or at least go over it for the synoptic essay tomorrow?
    I'm not sure whether I should or not, as i haven't got much time left
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    For the essay, if, say, we mention 3-4 topics from units 1,2 and 4, do we still 'have' to mention something from unit 5? Or does that not matter, since its synoptic? Thanks
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    (Original post by cor_fortis)
    Different sources say different things....I hate AQA.
    And the thing is looking at past questions from all units they pull information from multiple sources. Not just the "endorsed" NT book
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    (Original post by NRican)
    Not specifically although it may help you in the essay, just learn germ line , somatic and how somatic isn't effective as cells die etc.
    Thanks, what about using the harmless virus, gene wrapped in lipid molecules and SCID? I just don't think they're worth learning if we don't need them and the specification isn't very clear on them.
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    (Original post by johnsoloman)
    Hey, is anyone bothering to learn AS biology or at least go over it for the synoptic essay tomorrow?
    I'm not sure whether I should or not, as i haven't got much time left
    I'm not bothering too much with AS either. I know all the basics from AS and I'll just try realte anything that comes into mind to the essay question without going into too much detail.
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    (Original post by cor_fortis)
    DNA is the only one that contains Thymine. All other RNA Uracil instead.
    dna- largest
    rna-second largest-
    trna-smallest
    dna-mostly in the nucleus
    trna-made in the nucleus, found in cytoplasm mostly
    rna- made in nucleus-found in cytoplasm mostly
    dna- most chemically stable
    rna- least stable broken down quicker
    trna- more stable than rna less than dna


    also other difference, such as the bases, with u in trna and rna, also trna and dna have hydrogen bonding, yet rna and trna are similar in that they are made of a single polynuclotide strand
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    (Original post by strawberry_cake)
    For the essay, if, say, we mention 3-4 topics from units 1,2 and 4, do we still 'have' to mention something from unit 5? Or does that not matter, since its synoptic? Thanks
    Nope, as long as it's all relevant.
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    (Original post by johnsoloman)
    Hey, is anyone bothering to learn AS biology or at least go over it for the synoptic essay tomorrow?
    I'm not sure whether I should or not, as i haven't got much time left
    Gloss over main principles, diffusion, osmosis, protein structue/enzymes, carbs, transpiration in plants etc.
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    Can someone please explain to me the use of reverse transcriptase and how it synthesisis cDNA from RNA? (any conditions please include)
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    (Original post by johnsoloman)
    Hey, is anyone bothering to learn AS biology or at least go over it for the synoptic essay tomorrow?
    I'm not sure whether I should or not, as i haven't got much time left
    I've briefly looked back over it for some bacteria stuff and the DNA stuff as that fits in with a lot of the Unit 5. But not especially. Just flicking through it now because I got fed up with Unit 5.
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    That my problem, with all the gene technology stuff, why do you used restriction endonucleases to 'cut' the fragment when you are going to sequence it, how do you know what restriction endonucleases to use?!
    Also, are neurotransmitter's hormones?
    Thanks guys! So nervous!
    xxx
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    (Original post by Sparkly-Star)
    Do we really need to know how DNA are introduced to host cells? When plasmids get mixed together in a medium with calcium cells and all that? =/
    I'm pretty sure we don't. Its not on the specification
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    (Original post by Stirlo)
    And the thing is looking at past questions from all units they pull information from multiple sources. Not just the "endorsed" NT book
    And I found that the question about IAA on the specimen paper was actually pulled from a 2003 paper of either the old spec or a different exam board. blasphemy
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    whats the difference between dna probe and primer? why cant a dna probe act as a primer??? dont get the difference? i know what they're roles are put cant a dna probe do what a primer does?
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    Gas exchange in organims. Few mistakes here and there but oh well. The info is taken from various sources.

    Gas Exchange in Living Organisms
    In this essay, I am going to outline the process of gas exchange within several types of organisms.

    Fick’s law states that the rate of diffusion across a membrane is directly proportional to the concentration gradient of the substance on the two sides of the membrane, which is also inversely related to the thickness of the membrane. Therefore, to increase efficiency of gas exchange between surfaces requires a large surface area: volume ratio, a thin partially membrane, a movement of the environmental medium and a movement of an internal medium to maintain a diffusion gradient.

    Single-celled organisms, such as bacteria and protozoa, are in constant contact with their external environment. Being small, they have a large surface area: volume ratio that means they rely on diffusion for the exchange of gasses. These organisms are covered only by a cell-surface membrane, therefore oxygen, used for respiration, is absorbed across their body surface. In the same way, the co2 waste product produced in the link reaction and Krebs cycle of aerobic respiration, diffuses out through their body surface.

    Most insects are terrestrial organisms. The problem of this is that they lose moisture from their body surface and become dehydrated: which may lead to desiccation. To compromise, they are adapted by having a small surface area: volume ratio as well as a thick waterproof covering. This need to conserve water is therefore in conflict with the need for efficient gas exchange. This indicates that insects cannot use their body surfaces to diffuse reparatory gasses. Instead, they have a special internal network of tubes that supply respiring tissues directly.

    Gas enters the insect through tine pores on the body surface, known as spiracles, after which it travels into trachea. From here, it diffuses into tracheoles, which are permeable to gasses and water. A supply of oxygen is delivered down a concentration gradient directly into the cells themselves. Meanwhile, the co2 produced by tissues during respiration travels along this internal network and out to atmosphere down its diffusion gradient. Many larger insects actively ventilate their respiratory systems, by raising and lowering the volumes of their abdomens with muscle contractions.
    Although the tracheal system is an efficient method of gas exchange, it has some limitations. It relies solely on diffusion to exchange gasses between the environment and cells. Diffusion pathways need to be short and so consequently, this limits the natural size that an insect can attain.

    In the presence of light, autotrophs take up atmospheric co2 for photosynthesis in order to synthesise the sugars needed for respiration. The gas exchange surface of the plant is on the underside of the leaf. Small pores, called stomata allow the diffusion of carbon dioxide into the air spaces as oxygen diffuses out. The thin structure and flat shape of the leaf minimises the diffusion pathway as well as offering an increased surface area for gaseous exchange. The air spaces between the mesophyll cells allow a rapid spreading and expansion of the CO2 up through the leaf towards the palisade cells down a concentration gradient, by diffusion. Here it diffuses through the plasma membrane, through the cytoplasm and on into the stroma of chloroplasts where it undergoes the Calvin cycle. Similarly, oxygen produced in respiration leaves the plant through the reverse pathway to that of co2.

    In contrary to respiratory gasses, water vapour is also lost through the plants gas exchange surface, the stomata. The evaporation of water through the gas exchange surface draws water up the xylem by cohesion-tension creating a transpiration stream that returns the water to the atmosphere.
    Aquatic organisms, namely fish, have a waterproof, gas-tight outer covering. Being relatively large, they have a small surface area: volume ratio. This means that their body surface alone in not adequate to supply their respiratory gasses and so, they too have developed a specialised gas exchange surface: gills.

    The gills are made up of stacks of gill filaments. Each filament has gill lamellae at right angles to itself which immensely increases the surface area of the gills for more efficient gas exchange. Gaseous exchange in fish relies on the principle of counter-current flow. This is where the flow of water over the gill lamellae and the flow of blood within them are in opposite direction. This helps maintain a steep diffusion gradient for oxygen across the entire length of the gill lamellae, which ensures that the blood absorbs about 80% of oxygen in the water. Blood acts as a transport medium, delivering oxygen to respiring tissues by mass transport.

    Mammals have a complex gaseous exchange system. This is because organisms have evolved into larger and more complex structures and so the tissues and organs from which they are made of have become more specialised and dependent upon each other. There therefore needs to be an efficient system that is able to meet the respiratory needs of an active mammal.
    Contraction allows ventilation of the lungs to take place in mammals. The contraction of the intercostal muscles and the flattening of the diaphragm moves the rib cage up and out, increasing the volume of the thorax. This decreases the pressure, allowing air to be drawn into the lungs down a pressure gradient. This introduces oxygen to the gas exchange surface, the epithelium of the alveoli of the lungs. This ventilates the epithelial cells of the alveoli, allowing oxygen to diffuse through the membrane of the cells. The oxygen then continues to diffuse through to the membrane of the red blood cells where it loads to haemoglobin, forming oxyhaemoglobin.

    Red blood cells themselves are small cells that have a biconcave shape that can flex easily and offer a high surface area of contact with the capillary walls for efficient gas exchange. This reduces the diffusion pathway of the oxygen and carbon dioxide, increasing gas exchange rates. An absence of organelles also increases the room available for the haemoglobin, each molecule of which can load four oxygen molecules.

    On contraction of the ventricles, the pressure forces the red blood cells through the body to regions where the partial pressure of oxygen is lower. These regions are that of respiring tissue which release co2. Co2 decreases pH around its immediate vicinity, which changes the shape of the haemoglobin molecule in red blood cells, to one that has a lower affinity to oxygen: thus, oxygen is released. Hydrostatic pressure forces the oxygen and other small molecules into the respiring tissues through the formation of a tissue fluid that allows aerobic respiration to take place, which ultimately leads to the production of ATP. Some co2 now binds with the haemoglobin molecules, forming carbaminoglobin, which is transported to the alveoli for gas exchange.

    Relaxation of the intercostal muscle’s actin and myosin protein filaments and the arching of the diaphragm move the rib cage down and in, decreasing the volume of the thorax and increasing the pressure in the lungs to higher than atmospheric. This creates a pressure gradient that forces co2 back though the respiratory system and back out into the atmosphere.
 
 
 
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