~wings~
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Hi,
This is my first thread so i'm not sure how it all works, but i'm giving it a go

There seems to be loads of sites for english and psychology where people share the essays that they've done for the subject...but none for biology!!
WHY!?!?!?!

Unit 8, AQA biology has a massive synoptic essay question at the end of it, and i'm really struggling with them - I'm going to post a couple (of mediocre) essays that i've already done, and HOPEFULLY. More will post and we'll build up a nice load of essays to revise from.

That is the plan!


PLEASE do not use this as a chat thread! Only post essays or essay plans...

Thanks

And good luck for the summer exams!!!
=]
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~wings~
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Enzymes in Biotechnology

Enzymes are globular proteins used as biological catalysts, they speed up the rate of chemical reactions. The essential role of the enzyme is to provide an active site, which has a complimentary shape to the molecules that bind there. Substrates are converted to products through the formation of an enzyme-substrate complex. To be effective in a production process the enzyme molecules must be brought into maximum contact with the substrate molecules.
For the purposes of this essay, biotechnology includes Recombinant DNA technology, bio-detergents, Biological fingerprinting and PCR.
In recombinant DNA technology, the DNA from one organism is combined with the DNA from another organism. Often this involves inserting human DNA into the DNA of another organism. When these genetically engineered organisms are cultured, they produce human protein.
When cells make a protein, they first transcribe its gene into a molecule of mRNA. mRNA molecules carry genes, for example, the gene that codes for Insulin. By finding molecules of insulin mRNA they can be used to make artificial insulin genes. To do this, the enzyme reverse-transcriptase is used. This enzyme speeds up the production of cDNA from mRNA.
Once the target gene has been located using a DNA probe, enzymes called restriction endonucleases (or restriction enzymes) control the process of removing it from the chromosome. There are many different restriction enzymes and each ‘cuts’ DNA at a different base sequence.
When the gene has been isolated using the restriction enzyme it is inserted into a vector that has been ‘cut’ with the same restriction enzyme to produce complimentary ‘sticky ends’. For this insertion to be successful, the enzyme ligase must be used to control the process of joining together the sticky ends of the vector and the sticky ends of the gene.
Using this gene technology, bacteria has been produced that can help to reduce pollution by removing existing pollutants and by introducing cleaner industrial processes.
Spillages from oil tankers are a major source of pollution at sea. Although detergents can be used to remove the oil, these detergents can be very harmful to marine life. However, naturally occurring ‘oil-eating’ bacteria are able to oxidise hydrocarbons into carbon dioxide. The genes that enable them to do this are often carried on plasmids. This has enabled the transfer of these genes into marine bacteria. As a result, genetically engineered bacteria can now be used to deal with oil spills.
Another aspect of enzymes in biotechnology that has proven to be particularly useful is in DNA profiling. This is a way of making a pattern from pieces of DNA cut with restriction enzymes. As everybody has different DNA, the pattern, or fingerprint, is unique to each individual.
This works because within the non-coding regions between genes, there are short sequences of bases called core sequences that repeat themselves over and over again. These repeating regions of DNA are called minisatellites. Different individuals have different numbers of repeated core sequences. The greater the number of repeats, the longer the minisatellite. Different people therefore have different sized minisatellites.
The technique for making a DNA fingerprint can be divided into four main steps: Extraction; digestion; separation and hybridisation.
In Digestion, certain restriction enzymes are added to the DNA to cut it. These enzymes recognise specific base sequences and so cut at specific points, close to, but not within the minisatellite region, thus leaving the minisatellite intact. This process produces a number of DNA fragments of different lengths, which are then separated out using electrophoresis to form a unique pattern.
In many instances there is insufficient DNA available for a genetic fingerprint test. This problem is overcome by using the polymerase chain reaction (PCR). PCR involves the repeated replication of DNA in a test-tube, doubling the amount with each replication cycle.
After heating the DNA to separate the double strands, the enzyme DNA polymerase, four different free nucleotides and DNA primers are added. As the mixture cools, the primers join to the DNA at either end of the region that is to be amplified. The enzyme DNA polymerase controls the ‘joining up’ of the free nucleotides to complete the strands. In this way, DNA is replicated, producing two double-stranded molecules.
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~wings~
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How nitrogen-containing substances are made available to and used by living organisms. – June 08

In the nitrogen cycle, plants take up nitrate ions from the soil. They are absorbed through the roots by active transport and are used to produce proteins and other nitrogen containing compounds in plant cells.
Primary consumers then feed on plants and the proteins in their food are digested to form amino acids. The amino acids are absorbed from the gut and built up into proteins which make up the tissues of the primary consumers. The same processes occur when the primary consumer is eaten by a secondary consumer.
In this way, nitrogen is passed from one trophic level to the next through the food web.

Plants need nitrogen for amino acid, protein and nucleotide synthesis. However, they cannot use nitrogen gas from the atmosphere.
Nitrogen gas in the atmosphere can be made available to plants by nitrogen fixation. This term refers to a number of processes which involve the conversion of nitrogen gas to nitrogen-containing substances and these processes all require a significant amount of energy.
A nitrogen molecule consists of two atoms, and the molecules have to be split before nitrogen fixation can take place.
One of the methods of fixing nitrogen is through lightning. During a thunderstorm, the electrical energy in lightning allows nitrogen and oxygen to combine to form various oxides of nitrogen. Rain washes these compounds into the soil where they can be taken up by plants as nitrates.
In the UK, the amount of nitrogen fixed by lightning is small, whereas in some parts of the tropics, violent thunderstorms are common and are an important way of fixing nitrogen.
An industrial process used in fixing nitrogen is the Haber process, which combines nitrogen and hydrogen to produce ammonia. The reactions take place at high temperatures and pressures and require the presence of a catalyst. A lot of the ammonia produced by the Haber process is used to make fertilizers which are added to the soil.
Already in the soil are micro-organisms, some of which are free living nitrogen-fixing bacteria. These bacteria reduce nitrogen to ammonia, using the enzyme nitrogenase as a catalyst for this reaction. Nitrogenase, however, is inhibited by the presence of oxygen and so many nitrogen-fixing bacteria have adaptations which ensure that anaerobic conditions exist in the parts of the cells involved in nitrogen fixation.
When organisms die, the nitrogen-containing organic substances which they contain are digested by saprobiotic bacteria and ammonia is released.
Another group of bacteria, the nitrifying bacteria then convert ammonia to nitrites and nitrates.
Under anaerobic conditions (e.g. in waterlogged soil), denitrifying bacteria are found in large numbers. These bacteria are able to use nitrate instead of oxygen as an electron acceptor in the respiratory pathway. The reaction involves reduction of nitrate to nitrogen gas. This nitrogen escapes and is no longer available to plants.

The movement of nitrogen from atmosphere to living organisms and back into the atmosphere exists as a continuous, self-sustaining cycle. However, human activities such as deforestation can affect this cycle by causing reduced input to the nitrogen cycle, slower and reduced recycling of nitrates and increased loss of nitrates by leaching.
This causes the soil to lose fertility, meaning it can support lower numbers and fewer species of plants, leading to a lowered diversity.
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nie-wiem
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any ideas what the essay could be on? predictions?
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nie-wiem
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i've noticed there are no questions on lipids and genetic eng in aqa...
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jaison2
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There's only a limited number of titles which can be asked which will cover the whole course! The huge ones are:
Function and importance of proteins! (DNA, facilitated diffusion etc etc etc)
The importance of water in an organism! (Photosynthesis, Blood plasma etc)
Cells and their structure in relation to their function (Sperm cells have a tail, red blood cells are bi-concave to increase surface area, nerve cells have long axons etc etc etc)
Transportation within cells and an organism! (Diffusion, facilitated diffusion, active transport etc etc etc..)

Only 16 marks out of the 25 for the essay are for the "stuff" you inlcude! The rest is all for grammar, presentation and how much you relate to the whole course. And remember, the examiners realise that we are writing this essay in the space of 45 mins so they wont be overly harsh when marking
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Sarah_279
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Are the essays in this thread A grade?
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Kinkerz
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(Original post by jaison2)
There's only a limited number of titles which can be asked which will cover the whole course! The huge ones are:
Function and importance of proteins! (DNA, facilitated diffusion etc etc etc)
The importance of water in an organism! (Photosynthesis, Blood plasma etc)
Cells and their structure in relation to their function (Sperm cells have a tail, red blood cells are bi-concave to increase surface area, nerve cells have long axons etc etc etc)
Transportation within cells and an organism! (Diffusion, facilitated diffusion, active transport etc etc etc..)

Only 16 marks out of the 25 for the essay are for the "stuff" you inlcude! The rest is all for grammar, presentation and how much you relate to the whole course. And remember, the examiners realise that we are writing this essay in the space of 45 mins so they wont be overly harsh when marking
I think that's really really restricting.

What can you honestly say?
* Photolysis
* Cohesion-tension/root pressure/capilliarity
* Turgor in cells

Then things start getting tough.
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Amelia31
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Im so worried about this exam, theres never enough for me to say without looking in the textbook
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PkT1991
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Perhaps instead of writing an essay just brain storm ideas? Why the fuss on the essay anyways? Im more scared of the article reading then the essay and data handling
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PkT1991
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Also in the Nitrogen question could you not say how nitrogen is used as the base pairing for DNA, such as Adenine with Tyrosine and Guanine with Cytosine, and then discuss in RNA the tyronise is replaced by uracil.
And how by doing this nitrogen can form nucloetides to allow for mRNA production or semi conservative replication, and so then discuss further about protien production via amino acids, I'm sure thats one of the main ideas of how nitrogen would be used in living oragnisims.
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CyberLink
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The synopsis is marked based on a few things. Breadth of knowledge, meaning that using different parts of the syllabus from the 4 modules, I think there are 3 marks for this so if you only write the whole essay that only mentions stuff from one module you get one mark.
If you mention things that is taken from beyond the syllabus you would be given a maximum 2 bonus points for showing you do background reading, provided you don't get over 100%
Structure and grammar as well as use of key words also get you some merit.
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SomeStudent
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How did it go guys? Essay on use of water and ATP came up again, I was so surprised... Not sure about question 1 and 2 tho, they were bit difficult.
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jack252
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questions were pretty awkward.
water essay was good though =]
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xxruthxx
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hey has any one done a synoptic essay on factors effecting population growth if so could you post it or give me some pointers fanx
:p:
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Susie25
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For the water ones:
photolysis (ie in light dependant photosynthesis)
Oxidative phosphoralation(its a bi-product)
osmosis and chemical gradients
the lung (the surfactant)
hydrolysis and condensation reactions
as a solvent
the water cycle

In plants:
cohesion-tension theory
keeping cells turgid
transport of glucose and vitamins

Properties of water:
H2O is a polar molecule and so allows the idea of the fluid mozaic model (hydrophobic and hydrophylic)
Hydrogen bonds allowing a surface tension (important for animals such as pond scaters)

i dunno there must b TONNEEEEEESSS more.. but thats it 4 now and tbh it totally depends on the question
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greenpeas
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[QUOTE=~wings~]How nitrogen-containing substances are made available to and used by living organisms. – June 08

Good that takes me back! That's the one in my A2 exam!
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Fusilero
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Hmmm... a bit of simple elimination here.

The Specimen Paper had Temperature and Causes of Variation

The 2009 Paper had ATP and Water

The 2008 Paper had (a) The part played by the movement of substances across cell membranes in the functioning of different organs and organ systems.
OR
(b) The part played by enzymes in the functioning of different cells, tissues and organs.

The 2007 Paper had (a) Movements inside cells.
OR
(b) Transfers through ecosystems.

The 2006 Paper had (a) The transfer of substances containing carbon between organisms and between organisms and the environment
OR
(b) Cells are easy to distinguish by their shape. How are the shapes of cells related to their function?

I think we can just about assume it's going to be shape and functions of polymers, something to do with bacteria or cycles in biology.

Or how behavioural responses cause shrews to maintain themselves in a favourable faunagoo free environment. :yep:
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Susie25
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haha we'll i'm literally pro at all that shrew stuff now so i'm sooooooooooooo doing that one!:woo:
i dnt think u can reli do elimination tho.. cause questions do repet themselves a lot and there are so many other possible essay titles that they could choose.. something on C02 or protiens or the importance of negative and positive feedback (in which case i'm TOTALLY screwed!)
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FMercury
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so how is everyone going about trying to revise for the synoptic essay? im not quite sure how it is best to tackle this one.
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