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    Hey!

    There was a similar thread for biology revision where people have started passing back questions and answers for revision: (http://www.thestudentroom.co.uk/show...php?t=1121506). I want to try the same thing here with people from my class at school (though others on TSR can obviously join in too) since its a good revsion tool.

    I want there to be one rule though. You have to attempt the question using only your own knowledge and type it up. You then use your books to type a textbook answer, that way you learn it and you don't make a mistake and confuse others and yourself. Whether you keep the original answer on your post is your choice though. :p:

    Remember to ask your question at the end of your post!

    Here's my question:

    Explain why sex-linked diseases caused by recessive alleles are often more common in males.
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    The males have a shorter Y chromosome which means any alleles that normally appear on the X chromosome automatically appear as dominant as on the XY on the male there is only the X and no consequent allele to balance out a recessive allele.
    That was a poor answer lol

    What are the assumptions of the hardy weinberg principle? :woo:

    Sorry to intrude but this just seems quite an interesting idea for revision
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    No mutations
    Large population
    Random mating
    No selection
    No migration

    What happens in the light dependent reaction of photosynthesis?
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    Something.

    Light shines on chloroplast, electron excites, de-excites and moves down electron chain giving off energy, this energy is used to convert Pi + ADP to ATP, at the same time NADP becomes reduced NADP due to photolysis of water and electrons are given to the chloroplast because it's lost some.

    Something like that anyway, I have no idea; don't even want to go to the exam in a few days.

    Next poster: outline the krebs cycle.
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    Acetyl Coenzyme A (2 Carbon) joins a 4 carbon molecule to form citrate (6C). Two carbon dioxide molecules are lost whilst the molecule also reduces two NAD coenzyme molecules and produces energy to make one ATP molecule. A 4 carbon molecule is formed which then reduces an FAD coenzyme and another 2 NAD coenzymes, forming the original 4 carbon molecule which then adds on to another acetyl CoA, and it goes on.

    The Krebs cycle 'turns' twice for one molecule of glucose, so 4 CO2, 6 NADH, 2 FADH and 2 ATP are formed.

    Describe how you would complete the mark-capture-recapture technique.
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    you capture the animals mark them and then release them and wait for a given peirod of time before you recapture them and count the number of animals are marked.


    N1 x N2
    n
    N1 - the number firstn collected
    N2 - number collected in second sample
    n - number marked in seconded sample

    hope thats right haha

    Descirbe what happens in anerobic respiration?
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    of animals/bacteria, or plants/fungi?

    in animals/bacteria Pyruvate is reduced into lactate, freeing up the reduced NAD to continue glycolysis, providing the cell with ATP to prevent death

    in plants/fungi the pyruvate is decarboxylated and reduced, once again freeing up NAD to continue glycolysis, only instead of forming lactate, ethanol is formed.

    what process do plants carry out in photosynthesis to satisfy the 2:1 ratio of ATP:NADPH needed for the calvin cycle?
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    (Original post by Artymess)
    of animals/bacteria, or plants/fungi?

    in animals/bacteria Pyruvate is reduced into lactate, freeing up the reduced NAD to continue glycolysis, providing the cell with ATP to prevent death

    in plants/fungi the pyruvate is decarboxylated and reduced, once again freeing up NAD to continue glycolysis, only instead of forming lactate, ethanol is formed.

    what process do plants carry out in photosynthesis to satisfy the 2:1 ratio of ATP:NADPH needed for the calvin cycle?


    Light dependent reaction..?
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    Q. The mitochondria in muscles contain many cristae. Explain the advantage of this.
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    It provides a large surface area for the electron transfer chain to operate, allowing the manufacture of large amounts of ATP.

    Next poster-
    A farmer used Nitrogen containing fertiliser in the form of Ammonium sulfate to encourage the growth of his plants.
    i.) Is ammonium sulfate an organic fertiliser?
    ii.) What processes would need to occur before the plants could use the Nitrogen in the fertiliser?
    iii.) Suggest why using natural fertiliser would be better than using artificial fertiliser in a field where crops are rotated twice a year, every year.
    iv.) The farmer noticed that the yield increased with the addition of fertiliser upto a point, after which it began to decrease. Suggest and Explain why it began to decrease.
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    (Original post by Orihime)
    Light dependent reaction..?
    Cyclic Phosphorylation.
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    (Original post by Hippysnake)
    It provides a large surface area for the electron transfer chain to operate, allowing the manufacture of large amounts of ATP.

    Next poster-
    A farmer used Nitrogen containing fertiliser in the form of Ammonium sulfate to encourage the growth of his plants.
    i.) Is ammonium sulfate an organic fertiliser?

    No.

    ii.) What processes would need to occur before the plants could use the Nitrogen in the fertiliser?

    ammonification.. then oxidisation during nitrification

    iii.) Suggest why using natural fertiliser would be better than using artificial fertiliser in a field where crops are rotated twice a year, every year.

    the cost of re-applying artificial fertliser will be very high.

    iv.) The farmer noticed that the yield increased with the addition of fertiliser upto a point, after which it began to decrease. Suggest and Explain why it began to decrease.

    If the fertiliser concentration is very high; fast growing species are favoured meaning that non-required species of plants such as grass will compete with the required crop for nutrients; reducing the amount of nutrients available to the required crop for growth hence decreasing the yield.
    Nest poster: Explain the process of speciation.
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    When a population of species is seperated by either allopartic or sympartic methods, there is no interbreeding between the two populations and no gene flow. Mutations already exist in both populations and continue to occur independently in both populations. Different selection pressures in the two environments will cause differential reproductive success, those most adapted to survive in their respective conditions are more likely to reproduce and pass on their advantageous alleles. Overtime the gene pools of the two populations will diverge and they will become different species, such that even if the two populations were bought together again, they would not be able to produce fertile offspring.

    (At the poster above-
    Most of your answers were correct, but for Q3- we all know artificial fertiliser costs alot even if applied once a year. What I was looking for was an answer relating to deteriorating soil structure, which would be improved when natural fertilisers add organic matter to the soil.)

    Next Poster:
    In a recent study of birds in the Snowdonia National Park, it was found that four different species of bird both nested and fed in the same tree.
    Species A usually nested and fed at the top.
    Species B usually nested and fed at in the middle.
    Species C usually nested on either side of the canopy, and fed elsewhere.
    Species D usually nested just above the visible tree trunk and fed there as well.

    i.) What evidence is there to suggest that all four birds are definetly different species?
    ii.) What is the advantage of having different nesting and feeding sites to each species?
    b) A second species is introduced that nests at the top of the canopy, but feeds at the middle of the canopy. Further observation showed that this species was a very agressive competitor for food.
    Describe and Explain the changes in species composition you'd except to see.
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    Next Poster:
    In a recent study of birds in the Snowdonia National Park, it was found that four different species of bird both nested and fed in the same tree.
    Species A usually nested and fed at the top.
    Species B usually nested and fed at in the middle.
    Species C usually nested on either side of the canopy, and fed elsewhere.
    Species D usually nested just above the visible tree trunk and fed there as well.

    i.) What evidence is there to suggest that all four birds are definetly different species?
    ii.) What is the advantage of having different nesting and feeding sites to each species?
    b) A second species is introduced that nests at the top of the canopy, but feeds at the middle of the canopy. Further observation showed that this species was a very agressive competitor for food.
    Describe and Explain the changes in species composition you'd except to see.
    i) all the birds feed from different niches and areas suggesting different food is present in each area. Different species require a different diet to survive due to adapting to that environment.
    ii) Each area contains only one species of bird as different species are suited to a different ecological niche. There will therefore be less interspecific competition between organisms as only intraspecific competition is present in each area.
    b) As its an agressive competitor for food the population af species B would reduce. This is because there is greater interspecific competition in the middle level for food between the organisms. The population of the new species would increase due to it being such an agressive competitor for food.

    My answer is shameful next to yours above HippySnake :o:

    Next poster: Outline the main factors that can affect on the rate of photosynthesis. :yes:
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    "Outline the main factors that can affect on the rate of photosynthesis."

    There are three (arguably four) main factors that affect the rate of photosynthesis: atmospheric carbon dioxide concentration, light intensity, temperature, and atmospheric oxygen concentration in C3 plants. Others exist such as wavelength of light etc. that I won't go into.

    A high carbon dioxide concentration increases the number of reactions that rubisco catalyses. This means that GP is formed at a faster rate, increasing the rate that the products of the light-independent reaction, i.e. hexose sugars, are produced (more is produced in the same amount of time). However, too much carbon dioxide damages the leaves of the plant, so an optimum concentration is needed.

    An increase in light intensity affects the light-dependent reactions so that the rate of photosynthesis increases (due to more excited electrons at a faster rate, producing more ATP and NADPH for the the light-independent reaction) until the photosynthetic pigments in the thylakoid membranes have become saturated with light. The removal of light intensity will stop the excitement of electrons and so no ATP or NADPH will be produced. ATP and NADPH are needed in the light-independent reaction to convert glycerate 3-phosphate to to triose phophate (ATP provides the energy, NADPH provides hydrogen) and so no hexose sugars are formed and the GP is not regenerated into RuBP.

    An increase in temperature will increase the kinetic energy of the reactants of the light-independent stage, increasing the probability of RuBP combining with carbon dioxide. It also increases the efficiency of rubisco, the catalyst of the reaction between these two substrates. This increases the rate of photosynthesis. However, if the temperature gets too high, the enzyme rubisco becomes denatured as bonds break, so that the reaction cannot occur, reducing the rate of photosynthesis.

    Oxygen and carbon dioxide compete for the same active site on rubisco. Consequently, photorespiration occurs whereby RuBP is oxidised to form only one molecule of GP (as opposed to two) and some by-products, halving the efficiency of photosynthesis.

    Have fun with this one: :p:
    The green pigment in a particular plant is caused by the dominant allele G. The yellow pigment is caused by the recessive pigment g. Complete a genetic cross between two parents heterozygous for this. Show each stage (e.g. parent genotypes) clearly.
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    Drawing isnt my strong point so Ill explain it.

    Gg and Gg parents are both carriers

    GG - Green
    Gg - green hetrozugous - Carrier
    Gg - Green hetrozygous - Carrier
    gg - Yellow - affected

    3:1 ratio are green : yellow


    "define the differnce between oxidive and substrat level phosphorelation"

    ENJOY
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    Boring.
    Substrate- Direct donation of Pi to ADP.
    Oxidative- Chemiosis. Pumping of H+ into intermembranal space using energy lost from elections. Diffusing back through ATP synthase, rotating the molecule giving off energy that's used to combine ADP and Pi.

    NEXT POSTER-

    1.)Explain how grazing prevents succession. Suggest why grasses can survive being grazed upon, but smaller woody plants and shrubs cannot.
    2.) I was recently conducting a study into the investigation of the colour found under the wings of eagles. The recessive allele 'q' codes for the production of a purple pigmentation under the wing. The dominant allele 'p' codes for the formation of green pigmentation under the wing.

    A.)Define in terms of expression in the phenotype
    i) Dominant allele
    ii.) Recessive allele
    iii.) Codominance
    iv.) Hierarchy of dominance.

    B.) Explain why we cannot directly determine the genotype of an eagle with a green pigmentation. Suggest how we could determine the genotype.

    I remember deducing that there were 333 eagles in the population I was studying. I remember recapturing 143 on the second week I was there, and I recognised 46 from before.

    Ci) Suggest how I recognised them.
    ii) How many did I originally capture?
    iii) What presumptions did I make when estimating the population size.

    My data shows that 224 of the eagles had green pigmentation under their wings. Using this, suggest how many heterozygous individuals are there in the population.
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    1.)Explain how grazing prevents succession. Suggest why grasses can survive being grazed upon, but smaller woody plants and shrubs cannot.

    Succession is prevented as grazing stops the amount of growth of plant species needed to alter the environment, e.g. through the deomposition of matter that would not have been eaten. Grasses survive as their growth rate is fast enough between grazing to survive, whereas other plants cannot, and so don't photosynthesise, can't respire etc.

    2.) I was recently conducting a study into the investigation of the colour found under the wings of eagles. The recessive allele 'q' codes for the production of a purple pigmentation under the wing. The dominant allele 'p' codes for the formation of green pigmentation under the wing.

    A.)Define in terms of expression in the phenotype
    i) Dominant allele - This allele affects the phenotype when present and 'represses' a recessive allele in heterozygous genotypes.
    ii.) Recessive allele - This allele is expressed only if no dominant allele is present, i.e. in recessive homozygous genotypes.
    iii.) Codominance - both alleles affect the phenotype of a heterozygous genotype, and neither is dominant over the other. For example, alleles A and B are codominant and, together, produce blood type AB.
    iv.) Hierarchy of dominance - a form of animal social structure in which a linear ranking exists. each animal is dominant over those below it and submissive to those above it in the hierarchy - Why did I have to answer this?

    B.) Explain why we cannot directly determine the genotype of an eagle with a green pigmentation. Suggest how we could determine the genotype.

    An eagle with green pigmentation could be either heterozygous dominant (pq), or homozygous dominant (pp). A genetic cross between the eagle with a green pigmentation and an eagle with a known genotype (i.e. homozygous recessive (qq) could be carried out. If any offspring present the phenotype of purple pigmentation then the green pigmented parent was heterozygous. If none were produced, the parent was likely to be homozygous dominant.


    I remember deducing that there were 333 eagles in the population I was studying. I remember recapturing 143 on the second week I was there, and I recognised 46 from before - theoretically speaking?

    Ci) Suggest how I recognised them. You marked them the first time around, e.g. with a leg tag.
    ii) How many did I originally capture? eurgh... let me find that calculator. 333 x 46 = 15318. 15318 / 143 = 107.11 (so 107.)
    iii) What presumptions did I make when estimating the population size. There was no migration in and out of the population. No reproduction, deaths and births in the population. Marking did not affect behaviour or survival of the birds. And finally that random mixing occured between the marked and unmarked birds within the population.

    My data shows that 224 of the eagles had green pigmentation under their wings. Using this, suggest how many heterozygous individuals are there in the population. 224 / 333 = 0.67 = P squared. Square root = 0.82. P + Q = 1. 1 - 0.82 = 0.18 = Q. 2PQ = frequency of heterozygous individuals. 2 x 0.82 x 0.18 = 0.295. 0.295 x 333 = 98-99 heterozygous individuals.

    Although I enjoyed the challenge (and most likely got one or two wrong), I don't think many people would bother to answer such a long winded question for the sake of revision.

    My question:

    Define Directional Selection. If you can, explain why the curve on the graph moves to the right and why some new alleles appear on the extreme side that is becoming advantageous.
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    [QUOTE=jimmy303]1.)Explain how grazing prevents succession. Suggest why grasses can survive being grazed upon, but smaller woody plants and shrubs cannot.

    Succession is prevented as grazing stops the amount of growth of plant species needed to alter the environment, e.g. through the deomposition of matter that would not have been eaten. Grasses survive as their growth rate is fast enough between grazing to survive, whereas other plants cannot, and so don't photosynthesise, can't respire etc.

    Grass survives because their auxin (growh hormone) is secreted from the base of the plant so they can continue to grow despite their tips being eaten. With trees and shrubs the auxin is secreted from the tip so when the tip is eaten by animals it can no longer grow and therefore dies.
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    Describe the effect on the levels of GP, RuBP and TP of changing the Light Intensity.

    is photosynthesis in the AQA spec?
 
 
 
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