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    Hi everyone,

    I just did one of the essay style questions for the AQA A-Level Biology Paper 3 paper. I don't really trust myself to give an accurate mark so I was wondering if someone here would be kind enough to do so? Some feedback for improvement would also be really helpful. Here's the question and answer:

    Question 7: "The importance of nitrogen-containing substances in biological systems."

    Nitrogen is used in various biological molecules in plants. Thus, the nitrogen cycle plays a fundamental role in the growth of plants. Inert N2 from the atmosphere is fixed via nitrogen fixation by nitrogen-fixing bacteria and saprobiotic organisms. Ammonium is created which is converted into nitrite via nitrifying bacteria and then into nitrate. Nitrate is absorbed by plants and broken down into nitrogen for various products, such as amino acids and nucleic acids.
    Nitrogen also plays a large role in animals. Nitrogen is essential for amino acids and thus the synthesis of proteins that provide structure and function that allow them to live. They thus provide a necessary block for the creation of enzymes, structural proteins such as collagen, antibodies, hormones, intrinsic and extrinsic proteins in phospholipid bilayer, etc.
    Enzymes allow us to hydrolyse specific substrates into products due to the induced fit hypothesis. Proteins have a specific 3D active site that is complementary to a substrate and morph to fit it. This is important because it means lower activation energy for products to be formed. Enzymes play an essential role in the immune system. For instance, lysozymes are used to hydrolyse antigens in the phagosome of phagocytes.
    Enzymes are also used for the digestion of foods. The three principle enzyme groups are: proteases (which hydrolyse proteins), amylases (for carbohydrates) and lipases (for lipids). Carbohydrates have their glycosidic bonds broken to form maltose as saliva contains amylase. Proteins are broken down via pepsin in the stomach acid. There are three main pepsins: endopeptidases, exopeptidases and dipeptidases. Endopeptidases hydrolyse peptide bonds within the polypeptide chain, exopeptidases break bonds with terminal amino acids in a polypeptide chain and dipeptidases break apart dipeptides into single amino acids. In the small intestine, lactase hydrolyses lactose into glucose and galactose to be absorbed into the epithelium. Deficiency in lactase results in lactose buildup and bloating due to lowered water potential. Maltase hydrolyses maltose into glucose. Only monosaccharides can be absorbed into the bloodstream so it is important these enzymes function properly.
    Antibodies help agglutinate bacteria, making them easier to digest and release cytokines to signal phagocytes. Antibodies have an antibody-antigen complex which causes complementary antigens to bind to it. Due to this specificity, antibodies are monoclonal and are produced in mass by plasma cells when an infection is detected.
    Intrinsic and extrinsic proteins in the phospholipid bilayer have a host of functions: they provide rigidity to the membrane (fluid mosaic model), provide protein channels which allow for facilitated diffusion and active transport and receptors which trigger metabolic pathways within the cell when activated. Receptors allow cascade amplification to take place when ligands bind with them. For example, in hepatocytes, adrenaline binds to receptors which causes numerous cAMP molecules to be activated. Each cAMP molecule results in numerous protein kinase molecules to be produced which induce glycogenolysis to produce glucose into the bloodstream. Proteins can form with carbohydrates to make a glycocalyx, on the exterior of the membrane of a cell. This helps in cell communication.

    http://filestore.aqa.org.uk/sample-p...W-MS-JUN17.PDF
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    (Original post by Nerdcubed)
    Hi everyone,

    I just did one of the essay style questions for the AQA A-Level Biology Paper 3 paper. I don't really trust myself to give an accurate mark so I was wondering if someone here would be kind enough to do so? Some feedback for improvement would also be really helpful. Here's the question and answer:

    Question 7: "The importance of nitrogen-containing substances in biological systems."

    Nitrogen is used in various biological molecules in plants. Thus, the nitrogen cycle plays a fundamental role in the growth of plants. Inert N2 from the atmosphere is fixed via nitrogen fixation by nitrogen-fixing bacteria and saprobiotic organisms. Ammonium is created which is converted into nitrite via nitrifying bacteria and then into nitrate. Nitrate is absorbed by plants and broken down into nitrogen for various products, such as amino acids and nucleic acids.
    Nitrogen also plays a large role in animals. Nitrogen is essential for amino acids and thus the synthesis of proteins that provide structure and function that allow them to live. They thus provide a necessary block for the creation of enzymes, structural proteins such as collagen, antibodies, hormones, intrinsic and extrinsic proteins in phospholipid bilayer, etc.
    Enzymes allow us to hydrolyse specific substrates into products due to the induced fit hypothesis. Proteins have a specific 3D active site that is complementary to a substrate and morph to fit it. This is important because it means lower activation energy for products to be formed. Enzymes play an essential role in the immune system. For instance, lysozymes are used to hydrolyse antigens in the phagosome of phagocytes.
    Enzymes are also used for the digestion of foods. The three principle enzyme groups are: proteases (which hydrolyse proteins), amylases (for carbohydrates) and lipases (for lipids). Carbohydrates have their glycosidic bonds broken to form maltose as saliva contains amylase. Proteins are broken down via pepsin in the stomach acid. There are three main pepsins: endopeptidases, exopeptidases and dipeptidases. Endopeptidases hydrolyse peptide bonds within the polypeptide chain, exopeptidases break bonds with terminal amino acids in a polypeptide chain and dipeptidases break apart dipeptides into single amino acids. In the small intestine, lactase hydrolyses lactose into glucose and galactose to be absorbed into the epithelium. Deficiency in lactase results in lactose buildup and bloating due to lowered water potential. Maltase hydrolyses maltose into glucose. Only monosaccharides can be absorbed into the bloodstream so it is important these enzymes function properly.
    Antibodies help agglutinate bacteria, making them easier to digest and release cytokines to signal phagocytes. Antibodies have an antibody-antigen complex which causes complementary antigens to bind to it. Due to this specificity, antibodies are monoclonal and are produced in mass by plasma cells when an infection is detected.
    Intrinsic and extrinsic proteins in the phospholipid bilayer have a host of functions: they provide rigidity to the membrane (fluid mosaic model), provide protein channels which allow for facilitated diffusion and active transport and receptors which trigger metabolic pathways within the cell when activated. Receptors allow cascade amplification to take place when ligands bind with them. For example, in hepatocytes, adrenaline binds to receptors which causes numerous cAMP molecules to be activated. Each cAMP molecule results in numerous protein kinase molecules to be produced which induce glycogenolysis to produce glucose into the bloodstream. Proteins can form with carbohydrates to make a glycocalyx, on the exterior of the membrane of a cell. This helps in cell communication.

    http://filestore.aqa.org.uk/sample-p...W-MS-JUN17.PDF
    You missed talking about nucleotides ,and could talk about some key examples such as ATP,which gives you a lot to talk about and you could cleverly connect it to nucleotides involved in metabolism such as NADH, and FADH .

    You also missed a big one by just mentioning nucleic acids and not talking talking about them more in depth (DNA and RNA) or why they are important.That fits in nicely with proteins and you have not mentioned much on metabolism.

    You could also talk about peptide hormones such insulin.That would fit in with cell communication and receptors.

    You should perhaps mention proteins are modified after translation such as adding carbohydrates to them (glycoproteins ) or lipids (glycolipids).Talk about self antigens and non self antigens,which are glycoproteins.
    It connects beautifully with the immune stuff you are talking about.

    Here something not mentioned in your syllabus that might get extra points.Not all enzymes are proteins.Some are made of RNA instead of protein,we call them ribozymes.The rRNA in the ribosome is an example and is what actually catalyses the peptide bond formation in the ribosome,not the protein component.So there more to talk about.RNA can have its own functions that isn't coding for proteins.Another example of this is tRNA.

    Maybe try to say something about plants.The pigment chlorophyll key structure is a porphyrin ring,which has 4 nitrogen atoms and its the electrons in this ring that gets absorbed and excited in photosynthesis.
    Anyway,I think your essay is good and I like how it flows.Good luck .

    As for marks ,I would put this in the 16-20 mark range.For 21-25 ,you need to mention stuff beyond the course.Add some synoptic bits such as what I suggested and I would then put it 21-25 marks.
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    Most appreciated, thanks for taking the time to provide feedback. Fingers crossed!
 
 
 
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