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Biol 5 essay practice. - The Student Room

  • Thought I'd have a crack at a practice essay today. I thought it might be beneficial to get other people to analyse my attempts

    The causes of variation and its biological importance.


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    Variation between living organisms is almost certainly one of the most important features of all life on planet earth as a whole.
    Without both interspecific and intraspecific variation, Life as we know it would not exist.
    Muscles need ATP in order for humans and animals to move around, and hunt for food. The cells in our muscles contain a lot more mitochondria, than other cells due to the fact that the muscles require lots of energy to contract and therefore they need lots of mitochondria to help keep up the ATP production to its high demand. ATP is also vital in homeostasis in helping to maintain constant body temperatures e.g. mammals such as polar bears require lots of ATP to help store the heat and prevent it from being lost to the surroundings. Anabolic Reactions also requires ATP. Such as the production of proteins from amino acids (Protein Synthesis), the production of glycogen from glucose and the production of lipids, all require ATP to be formed. Active transport is a process that requires a lot of ATP, as it's the movement of substances against a concentration gradient. An example of this- energy from ATP may be used by carrier proteins to move molecules into the cell against the gradient. The Na / K pump is a carrier protein bringing K into cell and removing Na . In plants, root cells minerals also travel from a low concentration in the soil to a higher concentration within the cell, which requires energy. In conclusion, ATP is the most important energy source in living organisms. Obtained in different ways and amounts. ...read more.



    Variation between members of the same species, known as intraspecific variation, is one of the driving forces behind evolution through natural selection. Minute variations in organisms, brought about through mutations in their DNA can cause certain members of a community to be better adapted to their environment than others, making them more likely to breed successfully and pass on their superior genes.
    The Last process takes place on the Cristi of the mitochondria and is called the Electron Transport Chain. This is the most efficient stage of respiration where around 32 molecules of ATP may be produced via a series of redox (oxidation and reduction) reactions. The hydrogen ions are brought by the reduced NAD and reduced FAD; this replenishes the cells supply of hydrogen carriers. The hydrogen atoms are brought at different energy levels depending on the carrier (NAD at the higher energy level). Once these hydrogen ions(+)are on the electron transport chain they are moved along the chain, this happens because each successive carrier on the chain has a higher electro negativity than the carrier one before it, therefore the positive hydrogen ions are pulled along down the chain. While they are being pulled along they also participate in a series of redox reactions, which join the free phosphorous groups to ADP molecules to form the end ATP. (below diagram of Electron Transport Chain) ATP is only produced, as it is required. It releases energy by breaking off the last phosphate group on the phosphate chain, attached with a very unstable covalent bond; the bond is broken by hydrolysis (the addition of water) ...read more.

    Alternatively, differences in DNA may provide immunity to a disease which affects most members of a species. Although, if widespread disease can wipe out large amounts of a species, it will create a genetic bottleneck, where the size of a species gene pool is dramatically reduced and only the individuals with the mutated genes survive. This leads to a founder effect, where there is very little diversity in the species.
    Overall this is a good solid essay, clearly written and covering the major points. Towards the end it is less well written and looks a little rushed. The last two paragraphs could be extended quite a lot to cover other things on the syllabus. There are a couple of misunderstandings that could be cleared up with some more reading: ideally this essay would also have the names of the textbooks used in a bibliography at the bottom.

    A good example of this can be seen in the cheetah population. They suffer from many genetic problems caused by inbreeding, after hunting severely reduced their population.

    Variation between members of the same species can also be brought about through environmental factors.
    This student written piece of work is one of many that can be found in our AS and A Level Energy, Respiration & the Environment section.

    If a group of one species is separated into two groups, living in two distinctly different environments, they will adapt differently over time, even in one generation. Over many generations, these different adaptations will manifest themselves genetically, and the gene pools of the two separate populations will become very different. If the members of the same species become so different, that when brought back together, they can no longer breed, then they must now be classified as different species. This is one of the fundamental principles behind evolution by natural selection. New species arise through old ones adapting to their environment. The separation between two of the same species does not necessarily have to be a purely environmental one. For instance, a slight genetic mutation could cause a plant’s flowers to become a different colour. At this point, they would still be the same species. However, because of this change in colour, they would no longer be pollinated by the same insects as the rest of the species. In this way, the two gene pools would be separated, even though the two sets of plants still continue to live side by side.
    If there was no variation between species, then every organism would be attempting to occupy the same niche. Two species that try to occupy exactly the same niche cannot comfortably coexist, and so, a balanced ecosystem could not be established. Variation allows for ecosystems to remain balanced for very long periods of time, as each animal continuously adapts around their environment.
    This activates the molecule allowing a series of reactions to occur, first by splitting into 2 glycerate-3-phosphate molecules and then producing 2 NADH molecules and 4 ATP molecules in total (leaving 2 pyruvate molecules for the link reaction), with a net gain of 2 ATP molecules.

    Prey becomes better at avoiding predators, predators become better at chasing prey, and so on.

    There are two main types of selection, directional and stabilising.

    On a genetic level, variation can be brought about either during meiosis by a number of factors, or during mitosis by a mutation in the DNA. A mutation is a change in the order of bases in the DNA of an organism. There are two types of mutation, deletion and substitution. A deletion is where one base is lost from the DNA strand, and a substitution is where one base is replaced by another. If the order of bases changes, then this will change the way proteins in the organism are synthesised. A tiny change in the order of bases can have catastrophic consequences in the phenotype of an organism. For instance, the genetic condition cystic fibrosis is caused by just 3 base pairs being lost by a deletion type mutation in the DNA.

    In meiosis, which occurs only in organisms which reproduce sexually, variation in the genetic makeup of the gametes can be caused by “crossing over” of the chromosomes, and independent assortment. Since each gamete is not genetically identical to any other, random fertilisation, i.e. that the two gamete which eventually form the zygote are picked at random from millions, is also a cause of variation.

    Although each member of a species has the same genes, variation is caused by them being expressed in different ways. Different variations of the same gene are called alleles, and the combinations of ways in which these alleles are expressed in the phenotype of an individual causes variation.

    As humans, we have learned to exploit variation. Using techniques known as artificial selection, and controlling the breeding of animals, we can control how subsequent generations of a population will turn out. We can use this to our advantage in farming to give us cows which produce more milk, chickens which lay more eggs, or more bountiful crops. This technique is also what gave rise to the astonishing diversity of domesticated dog and cat breeds around the world today. Although they are all members of the same species, different breeds of dogs and cats look significantly different because of generations of selective breeding. Some people however, claim that this practice is ethically and morally incorrect and we should not control the breeding habits of animals.

    There are many models for calculation the genetic diversity and variation of a population, and for calculating the frequency of an allele in a population. One such model is the Hardy-Weinberg principle.


    There are parts which need expanding, and I'll work on it more later today. But this is what I came up with in 40 minutes. And thats roughly the time you're supposed to spend on it.
    It needs an end as well. Something about conservation I guess.
    Last edited by Jaziek; 21-06-2010 at 10:12.
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  • sam2192
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    • 21-06-2010 14:35
    I will just mention brief points

    -mutation
    -founder effect, bottleneck effect (possibly deforestation and artificial and natural selection)
    -Meiosis, rnadom crossover phase, independent sgregation
    -Isolation (speciation)
    -migration

    and to expand on the importance you could say:

    -antibiotic resistance
    -homozygous recessive disorders
    -keeping alleles that have resistance to future problems that may arise (more to do with plants)
    -prevent inbreeding, which causes disorders

    thats all I can think of, I could do with people doing one for "enzymes and their importance in plants and animals, I'm guessing it would be useful to know everything an enzyme is linked to
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  • Fusilero
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    • 21-06-2010 14:39
    Genetic bottlenecks, as far as I'm aware, do not lead to the founder affect. The founder affect is organisms moving somewhere else in small numbers (if I remember right)
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  • Mann18
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    • 21-06-2010 14:42
    Above looks like a damn good essay plan. Mutation- Insertion, deletion, substitution, independent segregation, crossing over, selection pressure: for the causes.

    Then importance as you've said, niches, resistance, species diversity.

    I wouldn't do this essay unless the other one was awful though, there's so much scope to ramble, and it may cost you relevance marks.
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    • 21-06-2010 14:43
    (Original post by Fusilero)
    Genetic bottlenecks, as far as I'm aware, do not lead to the founder affect. The founder affect is organisms moving somewhere else in small numbers (if I remember right)
    Yeah, small numbers of organisms moving somewhere, most likely with a gene pool of limited variety.
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    • 21-06-2010 14:46
    (Original post by Mann18)
    Above looks like a damn good essay plan. Mutation- Insertion, deletion, substitution, independent segregation, crossing over, selection pressure: for the causes.

    Then importance as you've said, niches, resistance, species diversity.

    I wouldn't do this essay unless the other one was awful though, there's so much scope to ramble, and it may cost you relevance marks.
    Hoping for the carbohydrate structure & function, temperature & biological processes or hormonal control essays. They should be easy.

    The hydrogen bond one would be good as well, I can put in a lot of extra detail from chemistry.
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    • 21-06-2010 14:59
    (Original post by Fusilero)
    Hoping for the carbohydrate structure & function, temperature & biological processes or hormonal control essays. They should be easy.

    The hydrogen bond one would be good as well, I can put in a lot of extra detail from chemistry.
    I'm hoping for one based around enzymes or ATP, maybe one about the importance of cycles. Would be sweeeet, and easy to get all 4 Units into the essay.
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    • 21-06-2010 15:05
    (Original post by Fusilero)
    Genetic bottlenecks, as far as I'm aware, do not lead to the founder affect. The founder affect is organisms moving somewhere else in small numbers (if I remember right)
    The founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population.

    Therefore, if an animal was hunted almost to extinction, and then the population was built back up, the founder effect would be relevant.
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  • PinkGothicLady
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    • 21-06-2010 15:06
    This
    The causes of variation and its biological importance.
    is the essay title I'd like to come up.. but wasn't that the title of one of the specimen paper essays? Hence the likelihood of it coming up in the exam is probably rather slim

    I'm hoping not for one on carbohydrates or hormones though :|
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    • 21-06-2010 15:06
    (Original post by Mann18)
    I'm hoping for one based around enzymes or ATP, maybe one about the importance of cycles. Would be sweeeet, and easy to get all 4 Units into the essay.
    Ugh. Enzymes. how many enzymes have we actually done?
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    • 21-06-2010 15:08
    (Original post by Fusilero)
    Ugh. Enzymes. how many enzymes have we actually done?
    You wouldn't have to name specific ones.
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    • 21-06-2010 15:10
    (Original post by Mann18)
    You wouldn't have to name specific ones.
    But then you could do practically every biochemical reaction we've done and say an enzyme was involved...


    Smart.
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    • 21-06-2010 15:13
    (Original post by Fusilero)
    But then you could do practically every biochemical reaction we've done and say an enzyme was involved...


    Smart.
    My apologies, you'd have to name specific ones where the mark scheme asks that we do: e.g. maltase. But rubisco isn't one that we need to know conversely.
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    • 21-06-2010 15:19
    I'm really hoping the really specific biochemistry ones don't come up.

    I'd love "cycles in biology" though, that one would be brilliant.
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    • 21-06-2010 15:32
    Enzymes would be nice I'd not really considered that could be a title! You could talk about catalase from waaaay back in Unit 1 (I'm assuming you're all doing AQA here), that enzyme in PCR, DNA synthesis enzymes, you could talk about the primary, secondary and tertiary structures.. heat stability, mutations etc.. it'd be great! It perhaps wouldn't even be that painful writing about carbohydrates from that angle..
    Last edited by PinkGothicLady; 21-06-2010 at 15:35.
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    • 21-06-2010 15:39
    Oh man, I'd love "transfer of materials" as a title.
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    • 21-06-2010 15:43
    (Original post by Jaziek)
    Oh man, I'd love "transfer of materials" as a title.
    Transfer of materials? I wouldn't even know how to begin that... what is that referring to? As in nitrogen and carbon cycles?
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    • 21-06-2010 15:50
    Come onnnn something about organic compounds
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    • 21-06-2010 15:56
    (Original post by PinkGothicLady)
    Transfer of materials? I wouldn't even know how to begin that... what is that referring to? As in nitrogen and carbon cycles?
    nah more osmosis, diffusion, active transport ect...

    eg, Jan 08 - The part played by the movement of substances across cell membranes in the functioning of different organs and organ systems.
    Last edited by Jaziek; 21-06-2010 at 15:58.
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    • 21-06-2010 16:00
    (Original post by Jaziek)
    nah more osmosis, diffusion, active transport ect...

    eg, Jan 08 - The part played by the movement of substances across cell membranes in the functioning of different organs and organ systems.
    Ahh I see.. then yes I agree that would be a great title.

    The essay is worth 25% of the exam isn't it? And the exam is worth 20% of the overal A2 grade?
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    Updated: June 21, 2010
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