VCE Biology Questions Thread

chimichurri

Question 4a in the VCAA 2021 Exam is confusing me a bit and I was wondering if someone could help 🙂

The question:
Varicella (chickenpox) is a highly contagious disease caused by the varicella zoster virus. A live, attenuated
varicella zoster virus vaccine is recommended for children at age 18 months. In Australia, this vaccine is
provided free of charge under the National Immunisation Program.
a. Once the varicella zoster virus vaccine is injected into the arm of a child, an immune response occurs.
Summarise the immune response that occurs within the child to result in long-term protection from
chickenpox. [5 marks]

The VCAA Marker's Guide:
A suitable answer was that the vaccine is taken up by, for example, macrophages and antigen presented on the surface of the cell. The antigen presenting cell moves into the lymphatic system and is taken to the lymph node. Helper T cell stimulates naïve B cells. Each B cell divides to produce plasma cells, which produce specific antibodies. B memory and or T memory cells are produced for long-term immunity
This was very well answered. Many students presented clear logical answers and demonstrated a sound understanding of how long-term immunity is achieved.

I was wondering why we are expected to talk about B cells and antibodies when this question is a virus? As viruses are intracellular pathogens shouldn't a response to this question focus on the cell-mediated response and thus T cells?

prettypink1881

chimichurri i think its because in a vaccine, teh virus is dead/weakened so it doesnt invade the cell, so its only recognised as extracellular and then b cell immunity occurs. hope this helps! 🙂

_sophiestudies_

chimichurri I agree with prettypink1881, but also, during a viral infection, usually both your cell-mediated and humoral responses occur. Cell-mediated response targets infected cells, but the humoral response will also be initiated because the cells lyse and release more viral particles into the extracellular environment. Viruses can be extracellular and intracellular, so both responses would be initiated. With a vaccines, both would be usually be stimulated, as mentioned in the answer by VCAA (they state that B and T memory cells are produced). A live attenuated virus in the vaccine will replicate using the person's cells but at a very low level (not enough to cause proper disease), meaning a cell-mediated response is necessary. However, some of virus won't be inside cells and will be in the blood, requiring the humoral response. Both responses almost always work together in the third line of defence (since almost all pathogens will be able to be extracellular and intracellular in some way, and there a exceptions to these processes anyway since biology is kinda like that ahaha).

chimichurri

prettypink1881 and _sophiestudies_ thank you both so much!!!! that makes sense 🙂 would bacterial infections be an exception? as in they only require a humoral response? as they are not invading cells?

_sophiestudies_

chimichurri not necessarily, since some bacteria can invade and infect cells. It's quite complex though, so usually at a VCE level, bacteria as deemed extracellular and viruses are deemed mostly intracellular. It's unlikely VCAA would ask a question about which pathogens are extracellular and which aren't, since it can become complicated.

chimichurri

hi!! I was just wondering how much we need to know about the geological time scale - for instance do we need to know the specific eons or when different species came to develop? How much of this overview [https://i0.wp.com/www.australianenvironmentaleducation.com.au/wp-content/uploads/2020/09/Geological-Timescale-v3-768x879.jpg?resize=768%2C879&ssl=1](https://) would we need to be familiar with? and for those who have the cambridge textbook, how much of chapter 10A is relevant?
thank you so so much!!

prettypink1881

chimichurri Hi, sorry for the late reply but I dont think it says anywhere on the study design that we need to know any specific periods.
but I've done a few practice tests that are centred around the study design and in regard to geological time scale, most of them had things about the order of life complexity that has evolved like from bacteria to archea then eukaryotes. I think if you get a question about geological time scale it will usually include all the context about the time period for the question you need to answer the question.
I don't have the cambridge textbook so I'm not sure, but I hope this helps!

Taaaa76

Hey guys, I just want some tips on exam prep.
Which exams should I buy and when should I do each exam? Harder or easier exams first etc.
Also how many should I do? I heard 20 exams should be the minimum

Meep<3

Taaaa76 I think you should start off with the easier ones so that you can easily tell in which areas you need to focus on and to build up your confidence. After a few I think maybe you could start the harder ones.I'm not sure about which companies are better, I think its best to ask your teacher. Hope this helps.

btw how is everyone else going with exam prep??

Taaaa76

Meep<3
Haven't started practice exams yet, I have only just started revising the content from semester 1 and I have a trial exam tomorrow. yikes

Taaaa76

I have a question from AOS 1 unit 3: Is a silencer the same as an operator? or is an operator only in prokaryotes and a silencer in eukaryotes?

Seb

Taaaa76 From what I know, the operator is where the repressor binds in the trp operon to inhibit transcription (trp repression) and the silencer simply prevents transcription of an operon.

Taaaa76

For the polymerase chain reaction, what are the temperatures for each stage?? Every single source says something different
Edrolo says:
90-95 for denaturisation
50-55 for annealing
72 for elongation
TSSM says:
98 for denatureisation
60 for annealing
72 for elongation

Like what am I supposed to write in the exam????

Meep<3

Taaaa76 Question 2 on the 2022 exam is about PCR and asks about the different temperatures at each step. This is the answer to that question from the examiner's report, so I think you should go off this.

The stages are:
• Stage 1: denaturation occurs at e.g. 94°C; DNA strands separate
• Stage 2: annealing occurs at e.g. 55°C to allow the primers to join
• Stage 3: extension occurs at e.g. 72°C; optimal temperature of Taq polymerase and adding of nucleotides occurs.

hope this helps

Taaaa76

Meep<3
Thank you so much this definitely helped

Taaaa76

I was doing a TSSM exam and I came across this question:
Lithium hydroxide is a chemical that removes carbon dioxide by chemically reacting with it. During an experiment, a pot plant is placed into a sealed container that contains lithium hydroxide. Identify what will occur to the rate of photosynthesis. Provide a reason to support your answer. (1 mark)
The answer was:
The rate of photosynthesis will decrease. No mark awarded but must be stated. AND Carbon dioxide is an essential reactant in the process of photosynthesis. When it is a limiting factor there are insufficient carbon dioxide molecules to combine with the hydrogen ions. Less glucose is therefore produced.

I didn't understand this part: When it is a limiting factor there are insufficient carbon dioxide molecules to combine with the hydrogen ions.

Does carbon dioxide normally bind to hydrogen ions in photosynthesis? Is this referring to the Hydrogen ions that NADPH transfers??

prettypink1881

Taaaa76 I think they are talking about the carbon dioxide that binds with hydrogen and oxygen to make glucose (C6H12O6) but I'm not completely sure. it would makre sense though because it correlates directly to the fact that less glucose would be produced.

hope this helps!

Taaaa76

prettypink1881

Thank you!
Would a question like that come on the exam? As in should I expect to have to write that CO2 wouldn't be able to bind hydrogen to produce glucose if this question came in the exam?

prettypink1881

Taaaa76 personally I don't think so, because vcaa stated that

"Students should understand that a biochemical pathway is a series of steps (which may occur at different
locations within a cell or, in the case of eukaryotic organisms, in different cells) from initial reactants to a final
product and that each step is facilitated by enzymes and coenzymes. Students should understand the inputs,
outputs and cellular locations of the light dependent and light independent stages of photosynthesis within
chloroplasts in C3 plants. They do not need to understand the specific details of
the mechanisms that underpin biochemical pathways involved in photosynthesis and cellular respiration."-I belivee this means you don't need to know about which elements bind to other elements.
My teacher also told me that TSSM usually has much harder questions that have some content that isn't examined in the vce exam.

Taaaa76

prettypink1881

That's a relief. Thanks for letting me know so quickly

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