VCE Biology Question Thread

[radiant roses]

From the 2017 NHT Exam, question 1(b):
My response was:
- missense mutation occurs so that single nucleotide change results in change in amino acid in HBB gene
- new amino acid may not have same chemical properties or orginal amino acid
- beta globin structure is changed
- results in altered haemoglobin molecule

I am not sure if my answer is correct or not.
The exam report says:
Both:
- changing primary structure (or a description of this)
- affects folding/secondary/tertiary structure (shape) of molecule or the quaternary structure may be affected as haemoglobin is made up of more than one sub-unit.

Would I only get 1 mark because I only talked about the amino acid primary structure?
To get the second mark, could I just have had included that the new amino acid changes the folding of the haemoglobin molecule?

[Geoo]

In the 2017 VCAA Exam,

Question 1C:
It asks about how the expression of a single gene can lead to the production or different proteins.

Can someone explain how that happens and why, I really have no clue.
Thank you

[Erutepa]

From the 2017 NHT Exam, question 1(b):
My response was:
- missense mutation occurs so that single nucleotide change results in change in amino acid in HBB gene
- new amino acid may not have same chemical properties or orginal amino acid
- beta globin structure is changed
- results in altered haemoglobin molecule

I am not sure if my answer is correct or not.
The exam report says:
Both:
- changing primary structure (or a description of this)
- affects folding/secondary/tertiary structure (shape) of molecule or the quaternary structure may be affected as haemoglobin is made up of more than one sub-unit.

Would I only get 1 mark because I only talked about the amino acid primary structure?
To get the second mark, could I just have had included that the new amino acid changes the folding of the haemoglobin molecule?

I would award the mark for describing a change in the primary structure (although it would be good to used the terminology of 'primary structure' in your response). While you described a change in structure, I think it's important to integrate the terminology of secondary, tertiary and quaternary structures in your response in order to get full marks.

In the 2017 VCAA Exam,

Question 1C:
It asks about how the expression of a single gene can lead to the production or different proteins.

Can someone explain how that happens and why, I really have no clue.
Thank you

This question wants you to talk about post transcriptional modification, specifically the variable splicing of pre mrna to produce mrna. Hopefully this points you in the right direction. 

[Evolio]

Thanks IThinkIFailed and Erutepa for the help!

From the 2017 exam, question 9 c ii, I was wondering why they said that the transformed bacteria wouldn't have ampilicillin resistance? Since the restriction enzyme used was BamH1, this means that the gene for tetracycline resistance was disrupted meaning that the transformed bacteria wouldn't have died if placed on tetracycline agar. Would this be correct?
From the same exam and question 9 b ii, I was wondering why VCAA didn't add the BamH1 recognition site on the plasmid even though the question specifically asked to do that?

Also, when talking about complement proteins, what should we talk about?
I know that we need to talk about them forming membrane attack complexes and lysing but I was wondering what other stuff we needed to know about their function and how they help?

[xenx]

Hey,
does DNA hybridisation require temperatures to separate DNA strands (95 and 55) and allow them to join back together, like PCR?
I usually write the temperatures in but would this be wrong

[Erutepa]

Thanks IThinkIFailed and Erutepa for the help!

From the 2017 exam, question 9 c ii, I was wondering why they said that the transformed bacteria wouldn't have ampilicillin resistance? Since the restriction enzyme used was BamH1, this means that the gene for tetracycline resistance was disrupted meaning that the transformed bacteria wouldn't have died if placed on tetracycline agar. Would this be correct?
From the same exam and question 9 b ii, I was wondering why VCAA didn't add the BamH1 recognition site on the plasmid even though the question specifically asked to do that?

Also, when talking about complement proteins, what should we talk about?
I know that we need to talk about them forming membrane attack complexes and lysing but I was wondering what other stuff we needed to know about their function and how they help?

1. Question 9 has come up before and some nice answers to it can be found here https://atarnotes.com/forum/index.php?topic=184382.0
But basically, ampicilin resistance is carried on the plasmid as the ampicilin gene is intact in the plasmid. As such, bacteria sucsessfully transformed will have ampicilin resistance, while those not sucsessfully transformed will not have ampicilin resistance and will die. This is what the examiners report says.
You seem to be getting confused between ampicilin gene and the tetracycline gene.

2. For the diagram in the examiners report, I think they just left out the label. The question asked you to label it so you should.

3. I would say that the main 3 functions are to:
Attract other immune cells function as chemoattractants.
Lyse the cell by forming a membrane attack complex
Enhance phagocytosis by binding to pathogens and acting as an opsonin.

Hey,
does DNA hybridisation require temperatures to separate DNA strands (95 and 55) and allow them to join back together, like PCR?
I usually write the temperatures in but would this be wrong

In the past they have just accepted heating and cooling. Specific temps are not needed for DNA hybridization, but are needed for PCR.

[radiant roses]

I was wondering if someone could clarify the answer to question 5(a)(ii) to the Tutesmart Biology Practice Exam.
I thought that a plant cell has more chloroplast if it is in an area with more sunlight, so that there can be more chlorophyll to capture that light energy?

The sample solutions say that:
"The cell with a higher number of chloroplasts is likely to be in an environment where it is exposed to a lower level of sunlight and as a result needs to maximise photosynthesis. Where cell B has a low number of chloroplasts as it is in a high light environment and resultingly needs a decreased number of chloroplasts to have an adequate rate of photosynthesis occurring."

[dev_xy]

I was wondering if someone could clarify the answer to question 5(a)(ii) to the Tutesmart Biology Practice Exam.
I thought that a plant cell has more chloroplast if it is in an area with more sunlight, so that there can be more chlorophyll to capture that light energy?

The sample solutions say that:
"The cell with a higher number of chloroplasts is likely to be in an environment where it is exposed to a lower level of sunlight and as a result needs to maximise photosynthesis. Where cell B has a low number of chloroplasts as it is in a high light environment and resultingly needs a decreased number of chloroplasts to have an adequate rate of photosynthesis occurring."

Have you ever owned a house plant? the answer is correct. This is because house plant rarely gets light this results in more chloroplast because the plant want to absorb as much light that it can get hands to. Think about it if u have 3 chloroplasts what are the odds that the chloroplast will absorb light (spoiler: less chance) so it is more likely to die.

[Bri MT]

I was wondering if someone could clarify the answer to question 5(a)(ii) to the Tutesmart Biology Practice Exam.
I thought that a plant cell has more chloroplast if it is in an area with more sunlight, so that there can be more chlorophyll to capture that light energy?

The sample solutions say that:
"The cell with a higher number of chloroplasts is likely to be in an environment where it is exposed to a lower level of sunlight and as a result needs to maximise photosynthesis. Where cell B has a low number of chloroplasts as it is in a high light environment and resultingly needs a decreased number of chloroplasts to have an adequate rate of photosynthesis occurring."

You're thinking in terms of wanting the plant to capture the available resources to the max, yeah?

The thing is, basically everything in biology comes with trade-offs, so maximising the amount of chloroplasts when you already have access to all the light you want isn't often the best way to go. E.g. if a plant is in a sunny environment it might be more important to invest in water-saving morphology since water's a limiting resource for photosynthesis (and important to plants for other reasons too)

[Didge123]

Hello!
I am very confused about humoral immunity. Sorry for the long post I hope it makes some sense! Do I need to mention that antigen presenting phagocytes engulf the pathogen and present the antigens on MHC 2 markers to begin with? then which process is correct...

1.
- B cell binds to specific antigen and engulf it and present it on MHC2 markers
- T helper cells with specific complementary receptor bind to antigen presented on B cell
- T helper cells release cytokines that activate B cells to proliferate ect....
OR
2.
- Phagocytes engulf and present
- T helper cells then bind to antigen and release cytokines that activate specific B cells to proliferate
OR
3.
- B cells bind to specific antigen
- Specific T helper cell also binds to the antigen
- This double binding causes proliferation of B cells
 
Thank you so much any help is appreciated!

[Didge123]

Hello!
I am very confused about humoral immunity. Sorry for the long post I hope it makes some sense! Do I need to mention that antigen presenting phagocytes engulf the pathogen and present the antigens on MHC 2 markers to begin with? then which process is correct...

1.
- B cell binds to specific antigen and engulf it and present it on MHC2 markers
- T helper cells with specific complementary receptor bind to antigen presented on B cell
- T helper cells release cytokines that activate B cells to proliferate ect....
OR
2.
- Phagocytes engulf and present
- T helper cells then bind to antigen and release cytokines that activate specific B cells to proliferate
OR
3.
- B cells bind to specific antigen
- Specific T helper cell also binds to the antigen
- This double binding causes proliferation of B cells
 
Thank you so much any help is appreciated!

[Evolio]

When talking about the humoral response, I mostly focus on the B cells undergoing clonal selection and expansion, to differentiate into B plasma cells and B memory cells after B cells have been activated by T helper because I think the main thing with humoral is antibodies, so i think you can skip the antigen presenting part and focus on antibody production.
I usually use number 2 when talking about the humoral response.

Please feel free to correct me if I'm wrong.

[dev_xy]

Hello!
I am very confused about humoral immunity. Sorry for the long post I hope it makes some sense! Do I need to mention that antigen presenting phagocytes engulf the pathogen and present the antigens on MHC 2 markers to begin with? then which process is correct...

1.
- B cell binds to specific antigen and engulf it and present it on MHC2 markers
- T helper cells with specific complementary receptor bind to antigen presented on B cell
- T helper cells release cytokines that activate B cells to proliferate ect....
OR
2.
- Phagocytes engulf and present
- T helper cells then bind to antigen and release cytokines that activate specific B cells to proliferate
OR
3.
- B cells bind to specific antigen
- Specific T helper cell also binds to the antigen
- This double binding causes proliferation of B cells
 
Thank you so much any help is appreciated!

All of the descriptions are vague.
It depends on the question, you don't just wanna list bunch of stuff.

Its incorrect to state "B cell binds to specific antigen and engulf it and present it on MHC2 markers" because that really isn't true.
- The chosen T helper cell finds the chosen Beta cell
- The T helper cell stimulates the Beta cell to undergo clonal expansion to produce plasma cells and B memory cells
(- The plasma cells produce specific antigens used to defend against the pathogen.. or.. The B memory cells give lasting immunity... so on and so forth)

again it depends on the question, and the above response may not be complete. Don't complicate things. use the word "chosen"

[dev_xy]

When talking about the humoral response, I mostly focus on the B cells undergoing clonal selection and expansion, to differentiate into B plasma cells and B memory cells after B cells have been activated by T helper because I think the main thing with humoral is antibodies, so i think you can skip the antigen presenting part and focus on antibody production.
I usually use number 2 when talking about the humoral response.

Please feel free to correct me if I'm wrong.

No2 is not specific and it's likely that you don't get marks. remember the markers want detailed answer.
What do the phagocytes engulf and what do they present? the response is too vague

[Erutepa]

All of the descriptions are vague.
It depends on the question, you don't just wanna list bunch of stuff.

Its incorrect to state "B cell binds to specific antigen and engulf it and present it on MHC2 markers" because that really isn't true.
- The chosen T helper cell finds the chosen Beta cell
- The T helper cell stimulates the Beta cell to undergo clonal expansion to produce plasma cells and B memory cells
(- The plasma cells produce specific antigens used to defend against the pathogen.. or.. The B memory cells give lasting immunity... so on and so forth)

again it depends on the question, and the above response may not be complete. Don't complicate things. use the word "chosen"

Just a couple of corrections to what you've said above - B cells do bind to free antigen, engulf it and present it on their MHC class II markers. This detail, however, seems to be beyond what VCAA wants you to know. I personally talked about it in my responses, but I am not aware of any past questions requiring you to know this, however, it is not incorrect to include this in your response. You should also be aware that B cells are different from Beta cells. B cells/B lymphocytes are the immune cells which are relevant here, while Beta cells are pancreatic cells that secrete insulin.

I do agree with the lack of depth though at some points. Some dot points are lacking full explanations and are not even sentences like 'phagocytes engulf and present'. You are free to use dot points for these responses, but you might want to fill them out with a bit more explanation.

For all your responses, it is not imperative that you talk about B cells binding to free antigen, engulfing and presenting it to Th cells (as mentioned above). However you should be talking about how Th cells are activated by antigen presentation, then release stimulatory cytokines activating the B cells and prompting them to rapidly proliferate and differentiate into plasma B cells and memory B cells. As Evolio mentioned, it's important to cater the response to what the question wants, so if the question is talking about antibodies, you need to explain further that antibodies are produced in large quantities by these plasma B cells.