Oxbridge Application Specialists
There are many questions in the public domain that have been asked of applicants to Cambridge looking to study Natural Sciences. Here, we’ll focus on questions that cover biology in particular. We’ve selected a range of questions from those that are simpler and can be readily covered with A Level knowledge, through to those that are more bizarre and require ‘out of the box’ thinking.
Let’s begin with a question that would require you to work through various different processes. You might begin this by breaking down the fact that they will face some problems that are universal to any organism, be it underwater or on land, and some that are unique to being underwater. Oxygenation and temperature, for example, are issues on land too. The temperature in certain seas, or in deeper water, might be much cooler – just as it would be in certain areas on land or at higher altitude. Meanwhile, oxygenation might be lower in certain pockets of water, whilst it could also be lower at altitude, again, on land.
Unlike land organisms, you might explain that fish are affected by pH changes. As an example, you might outline that at a very high pH (above 9) ammonium is converted to ammonia, which is fatal to fish. pH levels will also affect bacteria, which in turn would be necessary for the ecosystem in which the fish lives – they will likely clean the water, and alter nutrient levels. Additionally, fish are subject to pressure changes – something that would only affect a land organism if it were to reach an exceptionally high altitude. Of course, one would expect the fish to be adapted to the level at which it swims in the water and therefore have few problems with the pressure at lower altitudes of water. We might also highlight light levels being an issue at greater depths.
Lastly, we should highlight man’s effect on the oceans – plastic pollution, oil spills, and other detritus damaging habitats and creating issues for fish and other marine life.
With this question, you might not be expected to go into huge detail, but should show an ability to think ‘big picture’ and work with the tutor to discuss your points.
This is a question that relies more obviously on your A Level knowledge. You should explain that amino acids are organic molecules consisting of an amino group, a carboxyl group, and an R sidechain, and that they are the basic building blocks from which we are able to construct proteins – be they hormones, antibodies, etc. Regarding why there are only 20, the most widely-held theory is that redundancy of information reduces the risk of mutation. There are 64 possible DNA codons, of which four are start and stop codons. This means that 60 codons produce only 20 amino acids. Therefore a single amino acid can relate to multiple codons, which reduces the risk of translation errors, and increases fidelity. A codon could have one base altered, but produce the same amino acid as it was intended to.
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You should be aware of the current system of domain, kingdom, phylum, class, order, family, genus, species. The system originated in 1758, codified by Carl Linnaeus, and is therefore referred to as Linnaean taxonomy. Originally there were 5 ranks, and now there are eight as above. However, understanding what a rank means is difficult and there’s often no clear definition. Even the concept of a ‘species’ is hard to define, and there are many different definitions used by biologists.. The system has changed consistently, with domains being proposed recently in 1990, for example. Given that the general public has no conception of what a rank is in our taxonomic system, we might argue that they are unfit for purpose when trying to communicate with non-scientists. We might highlight alternate systems, like the phylocode, which tries to more accurately classify organisms into their phyla. It looks to define a common ancestor and then use phylogenetics, and has been touted as a better system which is less confusing.
This question could be approached through a few different avenues, although one is perhaps the most obvious. That is that the majority of the human population today can drink dairy without incident, whilst thousands of years ago, drinking milk as an adult would have resulted in illness. In general, the enzyme lactase is only produced in the young of species, rather than in adults as well. However, animal husbandry and the subsequent incorporation of milk and cheese into adult diets led to a slow process of genetic change that has seen the human population able to eat and drink dairy – as we produce lactase throughout our lives (unless one is lactose intolerant, of course).
A less obvious example is a dietary gene called FADS2, which we see different versions of in meat-eating versus plant-based societies. As an example, a vegetarian population in a certain area of India displayed a particular mutation of the FADS2 gene that allowed them to better process omega-3 and omega-6 that they obtained from their plant-based diets.
You should approach this by outlining that the two questions here have essentially the same answer. There is no one ‘cold virus,’ rather there are many different types. Colds can be caused by rhinoviruses, which are the majority, although coronaviruses and RSV are also common causative agents. There are more than 160 serotypes of rhinovirus.
A ‘cure’ for the common cold would really be vaccine (as the common cold is a self-limiting illness that doesn’t require a cure in the typical sense) – and trying to create a vaccine that could cover more than 160 different types of rhinovirus, as well as the myriad other causative agents, would be incredibly difficult, especially when compared to reward – the cost to reward ratio would not be worth it. A cold is not a significant enough issue to necessitate the research to try to create a vaccine.
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There are different types of flu vaccine with different mechanisms of action. In general, adults are given an inactivated cell-based vaccine, while children are given a live attenuated vaccine. Some influenza vaccines combat three different seasonal influenza viruses – these are trivalent vaccines. This is normal and includes influenza A, pandemic A, and one of two influenza B lineage viruses. More recently, vaccines have been produced which combat both influenza B lineage viruses (i.e. they combat four viruses).
Vaccination is annual due to the high rate of mutation of the viruses, meaning that new vaccines must be produced yearly to combat these changes.
Inactive virus vaccines do not cause influenza, but will display the same antigens, allowing the body to mount an immune response in the future. In a similar manner, live viruses – whilst they do contain the virus – are weakened, meaning that they do not cause influenza, although they will cause some mild flu-like symptoms.
The viruses targeted are updated annually by the WHO to reflect the circulating viruses.
I believe that there are two parts to this – we need to both be able to add new energy to our component being used, and this component needs to provide a suitable amount of energy.
The molecule in which biochemical energy is being stored acts as currency which is used for biochemical processes. A ‘loaded’ molecule must be unloaded, and in turn drive a process. For ATP, it can become ADP (or AMP). It can then be restored to ATP, and fuel further processes.
Hydrolysis of ATP is a suitable amount of energy to drive most of the body’s chemical reactions, whereas conversion of glucose to CO2 and water releases around 30x more energy, which is not suitable.
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