Find the key to application questions in VCE Biology

On the first page of every recent VCE Biology Exam Report, you’ll find a variation of this sentence:

“Students who set out their answers logically were more likely to gain marks than those who produced answers that appeared to be rushed and lacking in thought.”

When the chief examiner repeats the same thing six times in a row, you know it’s something you should be paying close attention to.

Unfortunate as it is, exam assessors have to mark hundreds of papers a day, which means that they won’t have time to scrutinise your answer if it’s in any way difficult to understand. This means that an answer which is well-structured and easy for your marker to follow is more likely to get marks.

This is why it can be extremely useful to develop skeleton structures for some of the major topics in Biology Units 3 and 4 that ask you to explain specific biological processes. These are step-by-step frameworks which you can adapt to the support the specific question you’re given. Not only do they help give logical structure to your answers, but they also prevent you from waffling on with extra information that probably isn’t necessary, saving you precious time.

While this concept can be applied to a variety of different question types, skeleton structures can be especially useful when explaining the processes of:

• Natural selection
• Cell signalling
• Developing immunity

At the end of the article, you’ll find a variety of original practice questions that you can tackle yourself to hone your skills and understanding.

Natural selection

This is a huge part of Biology Unit 4, so it’s worth knowing the four steps of natural selection like the back of your hand. The four general steps are:

1. Variation. In the population, there is genetic and phenotypic variation between individuals.
2. Selection. A selection pressure makes one phenotype more likely to survive than another.
3. Reproduction. That phenotype is more likely to reach reproductive maturity, reproduce, and pass on its genes to the next generation.
4. Evolution. Over time, the phenotype becomes more and more common.

So with these four steps in mind, let’s look at how we can adapt this skeleton answer to a new scenario:

The African elephant uses its large ears to fan itself, keeping itself cool in the hot African Savannah. Using natural selection, explain how the African elephant developed this adaptation. (4 marks)

We can take above framework, and make it specific to this scenario by specifying:

• what the original phenotypes might have been
• what selection pressure acted on them, and
• which phenotype was favoured by that selection pressure

1. Originally, there would have been elephants with large and small ears.
2. The selection pressure of heat made elephants with large ears more likely to survive than individuals with smaller ears.
3. Elephants with large ears were hence more likely to reach reproductive maturity, reproduce, and pass on the genes for big ears to the next generation.
4. Over evolutionary time, the big ear phenotype became more and more common.

Note: Not all questions on natural selection will follow this relatively simple format, so this exact, four-point structure won’t always fit. It’s up to you to adapt the answer to make sure you answer the particular question you’re being asked, so make sure you do lots of practice papers to experience as many different question variants as possible!

Cell signalling

‘Cell signalling molecule’ is a broad term given to any molecule that conveys a message from one cell to another. There’s massive variation in the types and properties of the molecules that can do this, as well as in the process of cell signalling itself. However, all the variations in this process boil down to three simple, generalised steps:

1. Reception. A signalling molecule (ligand) binds to a receptor on the cell surface (if it’s protein-based) or within the cell (if it’s lipid-based).
2. Transduction. This ligand-receptor interaction triggers a cascade of changes which relay and amplify the signal throughout the cell. These changes can include enzymes being activated, proteins being modified, and secondary messengers being produced.
3. Response. The cell’s behaviour changes in some way.

These three steps are quite general, so it helps to look at some specific examples of how cell signalling molecules bring about a cellular response:

Insulin (protein-based cell signalling molecule):

1. Reception: Insulin in the blood binds to insulin receptors on the surface of muscle cells.
2. Transduction: The receptor triggers a cascade of reactions which result in the activation of enzymes and proteins that help to absorb glucose.
3. Response: More glucose is absorbed from the blood.

Testosterone (steroid/lipid-based cell signalling molecule):

1. Reception: Testosterone diffuses through the cell membrane and binds to testosterone receptors in the cytosol.
2. Transduction: The testosterone-receptor complex acts as a transcription factor which travels to the nucleus and upregulates target genes (eg. those involved in cell growth and replication) by binding to their promoter regions.
3. Response: The cell grows and divides more rapidly.

Let’s use these three steps of cell signalling to answer a sample question:

Epidermal growth factor, EGF, is a peptide hormone which is involved in healing skin. Following a cut or burn, cells near the injured area will release EGF, which will stimulate fibroblast cells in the area to synthesise and secrete collagen. This helps to speed up the healing process.

Describe how EGF leads fibroblasts to have this response. (3 marks)

You probably won’t have heard of EGF or fibroblasts before, but we can use our skeleton structure to develop a well-structured answer regardless. To make your answer specific to the question, identify:

• To what receptor, and where, the signalling molecule will bind.
• How the signal will likely be amplified throughout the cell.
• What the final response will be.

1. EGF binds to receptors to EGF on the surface of the fibroblasts.
2. The binding of EGF triggers a cascade of changes, such as activation of enzymes and production of secondary messengers, which relay and amplify the signal throughout the cell.
3. The changes ultimately result in the increased expression of the collagen gene and secretion of collagen from the cell.

Developing immunity

Whether it’s through infection or a vaccination, the process of developing active immunity to a pathogen also happens to follow a general, four-step process, which again makes answering questions about it much more manageable.

1. Primary exposure. A person is exposed to a pathogen and/or its antigens.
2. Clonal selection. B and T cells undergo clonal selection to produce cells to fight the pathogen.
3. Memory. Once the infection is cleared, memory B and T cells remain in the lymph nodes.
4. Secondary exposure. If the person encounters the pathogen again, the memory B and T cells rapidly divide to clear the infection much faster and more efficiently than the primary exposure.

As an example, let’s see how we can use these steps to answer a questions hinting at us to explain how adaptive immunity works in this case:

Rabies is an infectious viral disease prevalent in parts of Asia and Africa. It is caused by the rabies lyssavirus pathogen.

The first successful vaccine for rabies was produced in 1885 by infecting rabbits with the virus, waiting a few days, and harvesting the viral particles that had been weakened by the rabbit’s immune defences. These weakened viral particles were then prepared in a solution and administered to a human. After this, when the individual was exposed to the rabies virus, he did not get sick. (4 marks)

Explain how this vaccine led the individual to develop immunity to the rabies lyssavirus.

Surprise surprise, our skeleton structure can help us develop a high-quality 4-mark answer here. From the question stem, try and identify:

• Which specific antigen(s) the individual is developing immunity towards.
• How the individual was originally exposed to the antigens (vaccine, infection, etc) and how the individual’s immune system responded.
• How the immune system responded when it encountered the antigen again.

1. The individual was exposed to the antigens of the rabies lyssavirus expressed by the weakened viral particles in the vaccine.
2. B and T cells specific to the rabies antigens underwent clonal selection to produce cells to help fight the pathogen.
3. Once the virus was cleared, memory B and T cells carrying receptors for the rabies antigens remained in the individual’s lymph nodes.
4. When the individual was exposed to the rabies virus, their memory B and T cells were able to divide and clear the infection much more quickly and effectively than during a primary response, allowing the individual to avoid becoming sick.

Practice questions

Here are a handful of questions which you can try your hand at yourself. See if you can incorporate the skeleton structures we’ve talked about in your responses!

1. The Texas coral snake is a highly venomous snake, easily distinguishable by its bright red and yellow scales. Due to its deadly nature, it is generally avoided by predators, such as birds and raccoons. The Mexican milk snake, which lives in the same geographic area as the Texas coral snake, shares an almost identical red and yellow scale pattern, making the two virtually indistinguishable. However, unlike the Texas coral snake, it has no venom.

Using natural selection theory, explain how, and why, the Mexican milk snake evolved its red and yellow scale pattern. (5 marks)

2. The great white shark is a highly successful marine predator, preying on fish, otters, seals and sea lions. Great white sharks are coloured blue-grey on the top, to allow them to blend in to the water and sea floor, and are coloured white on the bottom, to allow them to blend in with light entering the water from above.

Using natural selection theory, explain how the great white shark evolved this camouflage colour scheme. (4 marks)

3. Antidiuretic hormone (ADH) is a peptide hormone released by the brain when the body is dehydrated. When released, epithelial cells in the kidneys increase their production of a channel protein called aquaporin, which is inserted into the cell membrane. Aquaporin helps reabsorb water molecules from the urine.

Explain how the release of ADH leads to the described response by epithelial cells in the kidneys. (3 marks)

4. The varicella-zoster virus, which causes chickenpox, is estimated to have infected one in five Australians. It is commonly said that a child who develops chickenpox once will never get chickenpox again.

Using your knowledge of adaptive immunity processes, explain why a child who is infected with the varicella-zoster virus can only get chickenpox once, even if they are exposed to the virus again. (4 marks)

5. The ‘seasonal flu’ is caused by the influenza A virus, and is responsible for around 36,000 deaths every year. Influenza A is a unique virus in that it is capable of rapidly mutating its antigens every year, meaning that developing long-lasting immunity to the flu is very difficult.

a) With reference to the process of adaptive immunity, explain how an individual getting a flu vaccination will help protect them from getting the seasonal flu that year. (4 marks)

b) Why might the same individual not be immune to influenza A during the next year’s flu season? (1 mark)

In conclusion.

When you’re under the stress of exam conditions and you’re hit with an application-style question, being able to adapt an existing formula to a novel scenario can be a total lifesaver.

However, don’t just stop at what’s in this article! See if you can create skeleton structures for other key areas of content too – enzyme inhibition and PCR might be good places to start.

It’s easier said than done, but being able to share your knowledge in a logical and easily understandable way is what can really elevate your answers from ‘good’ to ‘great’.