Feedback for essay on AQA A Level Biology Paper 3

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Student_17362929
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I would really appreciate if someone would give me feedback for this essay. The other two exams didn't go very well and I know I need to do really well in paper 3 to do well.

Essay title : Hydrogen Bonds and their importance in living organisms

One of the ways that hydrogen bonds are used in living organisms is in-between a double stranded DNA helix. Hydrogen bonds are used to keep complimentary base pairs together for the maintenance of the DNA helical shape. The unzipping of hydrogen bonds inbetween DNA allows DNA replication to take place by semi-conservative replication. Hydrogen bonds also have other significant purposes in the structure of DNA such as preventing the reactive bases from corruption of chemicals by the complimentary base pairing of adenine and thymine; guanine and cytosine. Hence, hydrogen bonds prevent DNA from damage and allow DNA replication to take place. They also allow protein synthesis to occur because of hydrogen bonds in RNA and DNA molecules.

Protein synthesis consists of two main processes; Transcription and translation. This involves RNA nucleotides binding to the template strand of DNA which joins complimentary base pairs by hydrogen bonds. This forms pre-mrna which is spliced to remove introns that do not code for amino acids, and this ultimately forms a molecule of RNA. Hydrogen bonds are therefore important to the formation of polypeptides, such as enzymes which catalyse reactions such as the breakdown of larger molecules into smaller molecules.

Enzymes also contain hydrogen bonds in their secondary structures which is the foldings of the proteins which can either form an alpha helix or beta-pleated sheet. The foldings are determined by hydrogen bonds. The tertiary structure of proteins consists of extensive foldings of polypeptides and their interactions which include ionic bonds, disulfide bridges and hydrogen bonds. Enzymes are especially important in organisms because they serve several purposes such as metabolising reactions or in digestion. For instance, the hydrolysis of starch to maltose by salivary amylase and the hydrolysis of maltose to glucose by membrane-bound disacharidases. This allows glucose to diffuse into the blood by facilitated diffusion and broken down for respiration. This would otherwise not be possible without enzymes which contain hydrogen bonds.

Hydrogen bonds are equally important in plants as they are in living organisms. For example, hydrogen bonds can be used to join together lots of cellulose molecules, which form fibrils that can make plant cell walls strong and give the plant cell structural support. Without these bonds, plants wouldn't have a rigid structure, making them susceptible to osmotic lysis. Additionally, plant cells require hydrogen bonds to allow transpiration and hence translocation to take place. The dipolar nature of water molecules gives water important properties such as strong forces of attraction because of hydrogen bonds between water molecules. This allows a stream of water to be transported up the xylem by cohesion-tension. Without hydrogen bonds, water would not be pulled up the xylem by transpiration and water is equally important in translocation because water moves in from the xylem to the phloem by osmosis, which allows mass flow to take place and sugars to be transported the the sink for respiration or storage.




I haven't written this in timed conditions, but at this point I would like critical feedback on this essay. I need to do well in this to make up for Paper 1 and 2, and get in to university. Thank you for reading if you've gotten up to this point
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W00LFY
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Only 4 topics, this will hinder you from accessing those top marks so definitely include at least 5 topics. What you've written however is very concise, nothing irrelevant so keep that up. Just my take on it .
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Student_17362929
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(Original post by W00LFY)
18/25
Only 4 topics, this will hinder you from accessing those top marks so definitely include at least 5 topics. What you've written however is very concise, nothing irrelevant so keep that up. Just my take on it .
Thank you! I'll make sure to write on 5 topics just to be sure
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cbaforusernames
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Good essay but you will need to include key words such as DNA Polymerase, RNA Polymerase. You should also talk about why the stream of water is pulled up, it's due to transpiration from the leaves creating tension which pulls the water up. For DNA talk about how the hydrogen bonds provide strength. Talk about how mutations can cause different hydrogen bonds to be made in the secondary and tertiary structure. Talk about how this can result in an inactive enzyme, e.g in Tumor suppressor genes.
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