VCE Biology Question Thread

[Erutepa]

2013 examiners report says that memory B cells are “short lived”.
Is this true? Do they ‘die’ or something?
And approximately how long do they last?

regular plasma B cells require a constant stimulation from cytokines from both itself and from other immune factors in order for them to function. This is to prevent unnecessary immune responses that last too long. So whenever these cytokines stop being received by the plasma b cell, they will undergo apoptosis. This is the same for T cells aswell.
Memory B cells, however, do not have the same need for this cytokine stimulation and will not undergo apoptosis along with plasma B cells after the infection has mitigated such that these memory cells will continue circulating within the body.

Obviously, these memory cells are not immortal and (as with most things) will eventually die.
However, I am pretty sure the lifespan of memory B cells can change significantly in context to different pathogens (some pathogens more readily and strongly activate the adaptive immune system than others). I think this may relate to how some vaccines require many doses throughout a lifetime, while others achieve adequate stimulation just once.
(please correct me if I am wrong (not too sure about this last thing))

[C14M8S]

I've got a fair few questions to vomit out, I may as well do them all in one hit as opposed to drip-feeding them -
1) What immune cells are mainly involved in tissue rejection? I've heard both Cytotoxic T and B plasma cells in practice exams, I'm assuming the actual answer is Cytotoxic T...?

2) What is the difference between clonal selection, expansion and differentiation? I'm assuming selection is the process of not killing self cells, expansion is division and differentiation is becoming memory/effector cell?

3) Is the dating of two volcanic rock layers to date whatever's inside absolute? I'm assuming so.

4) Do I need to know much about the process of how aneuploidy arises and how chromosomes are distributed, or just the fact that aneuploidy exists and recognizing it?

5) Do plants that are exposed to less light produce more chloroplasts to be more efficient or less because they lack the resources to make them?

6) Do helper T and cytotoxic T cells have their own specific naive and memory cells i.e memory cytotoxic and helper cells and naive helper and cytotoxic cells?

7) Different cells use the same receptor for hydrophilic signalling molecules and incur different responses due to them being hooked up to different transduction pathways, correct?

[PhoenixxFire]

I've got a fair few questions to vomit out, I may as well do them all in one hit as opposed to drip-feeding them -
1) What immune cells are mainly involved in tissue rejection? I've heard both Cytotoxic T and B plasma cells in practice exams, I'm assuming the actual answer is Cytotoxic T...?

2) What is the difference between clonal selection, expansion and differentiation? I'm assuming selection is the process of not killing self cells, expansion is division and differentiation is becoming memory/effector cell?

3) Is the dating of two volcanic rock layers to date whatever's inside absolute? I'm assuming so.

4) Do I need to know much about the process of how aneuploidy arises and how chromosomes are distributed, or just the fact that aneuploidy exists and recognizing it?

5) Do plants that are exposed to less light produce more chloroplasts to be more efficient or less because they lack the resources to make them?

6) Do helper T and cytotoxic T cells have their own specific naive and memory cells i.e memory cytotoxic and helper cells and naive helper and cytotoxic cells?

7) Different cells use the same receptor for hydrophilic signalling molecules and incur different responses due to them being hooked up to different transduction pathways, correct?

1. Tc cells. Plasma B cells (the antibodies produced by them) can be involved in autoimmune diseases though. But for VCE just assume its Tc cells in tissue rejection.

2. Selection is when a naive cell binds it's antigen. The naive cell is 'selected'. The other two you have right. The not killing self cells things happens during maturation.

3. If it's inside it then yes. If the fossil is in a layer above or below it then no.

4. Nope. Just that it exists and is a type of mutation.

5. I'm not entirely sure on this, I've heard conflicting things. Plant development isn't on the study design though, you just need to know how the rate of photosynthesis changes in response to differing light intensities.

6. Yes.

7. Yep, not necessarily the same receptor, but it will be a receptor with the same specificity.

Is it just me or did anyone else find the 2017 VCAA exam to be really hard? It was probably the hardest VCAA exam so far like it was so time constrained (( I'm so worried what this years exam will be like now....

Worth noting that objectively it wasn’t that much harder than the 2016 exam.

Looking at the grade distributions for 2016/2017
A+ 188/190
A 175/173
B 138/137
C 94/94
So whilst it seemed harder, the state overall performed fairly similarly on both exams.

If you’re worried about the slabs of text then bring a highlighter in and highlight the important information as you read the question.

[Azim.m]

Could someone help me out? I don’t really get the solutions

[PhoenixxFire]

Could someone help me out? I don’t really get the solutions

It's so you know what the conditions are like before you start the experiment. Notice that the temperature and oxygen changed and then remained steady, if you'd started the experiment at 1 minute you might assume that the cockroach caused that change.

[persistent_insomniac]

Worth noting that objectively it wasn’t that much harder than the 2016 exam.

Looking at the grade distributions for 2016/2017
A+ 188/190
A 175/173
B 138/137
C 94/94
So whilst it seemed harder, the state overall performed fairly similarly on both exams.

If you’re worried about the slabs of text then bring a highlighter in and highlight the important information as you read the question.
[/quote]

Yeah I marked it and didn't do as bad as I thought but how do you read those grade distributions things? Like what does 188/190 mean? Thanks!

[PhoenixxFire]

Yeah I marked it and didn't do as bad as I thought but how do you read those grade distributions things? Like what does 188/190 mean? Thanks!

That's the A+ cutoff. So in 2016 you had to get 188/240 to get an A+, in 2017 you had to get 190/240

[sophiie]

Is molecular homology and structural morphology the same thing?

[PhoenixxFire]

Is molecular homology and structural morphology the same thing?

No, but they’re similar.
Molecular homology is comparing the similarities and differences in DNA/proteins between species whereas structural morphology is comparing body structure (e.g. the pentadactyl forelimb)

[AISHAB]

I'm a little confused ,is water an output of photosynthesis as well? I've watched edrolo and Douch has it in his diagram but not equation. In the Heinemann textbook it is also part of the photosynthesis equation, so was wondering, is it better to write:

6CO2 + 6H20 --> C6H12O6 + 6O2

OR

6CO2 + 12H20 --> C6H12O6 + 6O2 + 6H20

Thanks in advance!

[PhoenixxFire]

I'm a little confused ,is water an output of photosynthesis as well? I've watched edrolo and Douch has it in his diagram but not equation. In the Heinemann textbook it is also part of the photosynthesis equation, so was wondering, is it better to write:

6CO2 + 6H20 --> C6H12O6 + 6O2

OR

6CO2 + 12H20 --> C6H12O6 + 6O2 + 6H20

Thanks in advance!

You can use either, VCAA accepts both. The second one is the actual equation but you can use the simplified version if you want.

[AISHAB]

You can use either, VCAA accepts both. The second one is the actual equation but you can use the simplified version if you want.

Thanks!

[$noopDodd]

That's the A+ cutoff. So in 2016 you had to get 188/240 to get an A+, in 2017 you had to get 190/240

correct me if I'm wrong, but I think the 2013-2016 exams were out of 220 marks, indicating a significantly lower A+ cutoff last year (79%) compared to 2016's 85%

Got a couple of questions from VCAA 2017:

Is the reason chloroplasts have double membranes due to the outer membrane arising from endocytosis, or due to cyanobacteria having double membranes themselves? Seen differing views of this in the textbook and online
On MCQ 12 one of the incorrect options was that chloroplast and bacteria "store chlorophyll in their outer membrane".
Not sure if the reason it's incorrect is because the bacteria don't have an outer membrane or because they store chlorophyll in their inner membrane.

In the 2017 exam for the question (9c) about selection of bacterial cells which have been successfully transformed, I noticed the solutions didn't say anything about the tetracycline gene being disrupted as a method for selecting bacteria (which have taken up the recombinant plasmids (containing the foreign gene), rather than just any plasmids. Would we just have to interpret the question as implying that ALL of the plasmids being inserted are recombinant?

[Azim.m]

If I a question asks why there’s a great genetic variation in African than non-African populations, could we say that since Homo Sapiens migrated out of Africa, they could have been subject to the founders effect, hence having a low genetic diversity, whereas the Homo Sapiens in Africa were not? How else could I go about answering this?

[galaxy21]

correct me if I'm wrong, but I think the 2013-2016 exams were out of 220 marks, indicating a significantly lower A+ cutoff last year (79%) compared to 2016's 85%

The 2013-2016 Exams were out of 110 marks - the exams have increased by 10 marks with the new study design. The 220 is from grade distributions (they double the marks as two examiners are marking the exam)