HSC Biology Question Thread

[mhuss]

can someone please explain in simple terms the difference between T cells and B cells in the search for better health. i have done research on it, but i struggle to wrap my head around the concept.
thank youu

[jasn9776]

B-cell
lymphocyte produced and matured in the bone marrow (thus B cell)
humoral response: antibody producers. They respond to antigens, which are foreign markers or molecules.
.antibodies are like things that stick on the surface of antigens(foreign particles) and form a antigen-antibody complex which helps disable it and allow phagocytes to engulf it.

T cells
lymphocyte that comes from bone marrow but matures in thymus gland (thus T cell)
cell-mediated response: They respond to i guess to infected cells which can present to cytotoxic t-cells. SO basically the difference is T-cells respond to cells which are infected and present fragments of the invader to t-cells and B-cells respond to antigens which are like foreign substances.

T cells kill cells. Unlike B-cells, they specifically attack other cells by inserting chemicals into them and killing the cell whereas B-cells just produce antibodies and attack the foreign fragments/substances from afar. 

I'm not really that sure either but i'm pretty sure T-cells are intracellular and kill the invader that is inside the cell whilst B-cells are extracellular and kill what is not inside a cell.

[mhuss]

B-cell
lymphocyte produced and matured in the bone marrow (thus B cell)
humoral response: antibody producers. They respond to antigens, which are foreign markers or molecules.
.antibodies are like things that stick on the surface of antigens(foreign particles) and form a antigen-antibody complex which helps disable it and allow phagocytes to engulf it.

T cells
lymphocyte that comes from bone marrow but matures in thymus gland (thus T cell)
cell-mediated response: They respond to i guess to infected cells which can present to cytotoxic t-cells. SO basically the difference is T-cells respond to cells which are infected and present fragments of the invader to t-cells and B-cells respond to antigens which are like foreign substances.

T cells kill cells. Unlike B-cells, they specifically attack other cells by inserting chemicals into them and killing the cell whereas B-cells just produce antibodies and attack the foreign fragments/substances from afar. 

I'm not really that sure either but i'm pretty sure T-cells are intracellular and kill the invader that is inside the cell whilst B-cells are extracellular and kill what is not inside a cell.

makes a little more sense. thank you
xx

[cnimm2000]

Hey guys
Im a bit confused, for the interaction between T and B cells, do we just need to know the antibody mediated immunity?

[KT Nyunt]

Hey guys
Im a bit confused, for the interaction between T and B cells, do we just need to know the antibody mediated immunity?

Hello,
No, you'll definitely need to understand cell-mediated immunity as well. Here's a run down of everything B cells and T cells...

Interaction between B and T lymphocytes
-   Macrophages ingest antigens and display antigenic fragments on their MHCII molecules
-   Helper T cells recognise these fragments and secrete cytokines to activate B tells and T cells, making them begin cloning and differentiating for further assistance.

Clonal selection theory
-   Many B cells and T cells exist in the lymph nodes. Each B cell and T cell has unique receptors.
-   When a foreign particle invades the body, lymph fluid carries them (or their antigenic fragments) to the lymph node is recognised by the specific receptors of one of the B cells. This B cell is ‘selected’ and produces clones of itself with the same receptors
-   Antigen presenting cells with antigenic fragments travel to the lymph node. Its antigenic fragments are recognised by specific receptors of one of the T cells. This T cell is ‘selected and produces clones of itself with the same receptors

I've attached a table outlining all the types of B cells and T cells and their roles and an image I found online which sums up the whole process pretty nicely

Hope this helps

[Razeen25]

Hii,

For the dot point 'Discuss evidence for the mutagenic nature of radiation', since the directive term is a "Discuss", what points against evidence for the mutagenic nature of radiation would we use? Or do we not need to have points for and against?

Thank you!!

[Ace2018]

Hii,

For the dot point 'Discuss evidence for the mutagenic nature of radiation', since the directive term is a "Discuss", what points against evidence for the mutagenic nature of radiation would we use? Or do we not need to have points for and against?

Thank you!!

The NESA website () directs students to "Identify issues and provide points for and/or against" for discuss. Therefore, it is not necessary to talk about issues against. Besides, with this dot point you simply have to find various evidence of the ways that the exposure to radiation has the potential to cause mutation. For example, victims  of the Hiroshima and Nagasaki nuclear bomb show birth defect in offsprings.

Hope that helps!

[Razeen25]

The NESA website () directs students to "Identify issues and provide points for and/or against" for discuss. Therefore, it is not necessary to talk about issues against. Besides, with this dot point you simply have to find various evidence of the ways that the exposure to radiation has the potential to cause mutation. For example, victims  of the Hiroshima and Nagasaki nuclear bomb show birth defect in offsprings.

Hope that helps!

Thank you so much! I knew evidence for but wasn’t sure if we needed against. This clears it up!

[Razeen25]

Hii,

I'm confused over a 5 mark past trial question,

"Use the Darwin/Wallace theory of 'natural selection' to explain the increasing numbers of antibiotic-resistant bacteria AND how this knowledge can be used to reverse this resistance trend."

I understand the first half of the question, as it is just linking the way in which the theory of evolution is responsible for antibiotic resistance, but I don't understand how that knowledge can be used to reverse resistance. I thought antibiotic-resistance could be SLOWED through the use of narrow-spectrum antibiotics, finishing the course, etc, but reversed?

Any help would be appreciated!

[beeangkah]

Hi,

I'm struggling with the meiosis diagram-type questions where it asks to find the possible genotypes.

For instance these HSC questions
2002 Q22
2007 Q22d

After looking at sample answers, I can work backwards and see how it was answered, but I don't understand why it was done that way.

Could someone please explain the thought process on how to answer the above questions?

Thanks 

[KT Nyunt]

Hii,

I'm confused over a 5 mark past trial question,

"Use the Darwin/Wallace theory of 'natural selection' to explain the increasing numbers of antibiotic-resistant bacteria AND how this knowledge can be used to reverse this resistance trend."

I understand the first half of the question, as it is just linking the way in which the theory of evolution is responsible for antibiotic resistance, but I don't understand how that knowledge can be used to reverse resistance. I thought antibiotic-resistance could be SLOWED through the use of narrow-spectrum antibiotics, finishing the course, etc, but reversed?

Any help would be appreciated!

Yeah that's confusing. I think in the exam I would've just talked about how knowledge of antibiotic resistance leads to solutions that would slow this process (like the ones you've pointed out). I think this technically is what they're asking for - slowing down the fast moving trend I guess reverses the resistance trend... (if that makes any sense to you)

 It's not like strains of bacteria can de-evolve and become non-resistant. Maybe our B cells and T cells can evolve and become better at attacking bacterial infections??? I think this is just simply over complicating the question. It probably just wants you to talk about taking the full course and not overusing antibiotics on populations.

Hope this helps

[KT Nyunt]

Hi,

I'm struggling with the meiosis diagram-type questions where it asks to find the possible genotypes.

For instance these HSC questions
2002 Q22
2007 Q22d

After looking at sample answers, I can work backwards and see how it was answered, but I don't understand why it was done that way.

Could someone please explain the thought process on how to answer the above questions?

Thanks 

So for the 2002 paper with question 22, they've asked to construct a table listing possible genotypes that could be produced after meiosis with random segregation has occurred and the expected frequency of each genotype.
The cell features 3 pairs of homologous chromosomes. In meiosis this will divide into haploid cells like in the diagram if attached (see attachment). Note that a haploid cell has 1 chromatid of from each of the 3 homologous chromosomes pairs. So to find all the possible genotypes, we basically have to find all the possible combinations where one chromatid can be E or E, another can be B or b and the last one can be G or g
The possible combinations we can get are:
EBG
EBg
EbG
Ebg
As there are 4 of them and they all have an equal chance of being the genotype, they all have an expected frequency of 25%

For the 2007 paper, question 22d, make sure you:
1) show the difference between genes and alleles by defining them both
2) make reference to the diagram as well

A sample answer could be:

Spoiler

Genes are sections of DNA that code for the production of a specific polypeptide (e.g the section of DNA that codes for B or b). Whereas, alleles are variations of genes (e.g. B and b are variations of a gene)

Hope this helps 

[beeangkah]

So for the 2002 paper with question 22, they've asked to construct a table listing possible genotypes that could be produced after meiosis with random segregation has occurred and the expected frequency of each genotype.
The cell features 3 pairs of homologous chromosomes. In meiosis this will divide into haploid cells like in the diagram if attached (see attachment). Note that a haploid cell has 1 chromatid of from each of the 3 homologous chromosomes pairs. So to find all the possible genotypes, we basically have to find all the possible combinations where one chromatid can be E or E, another can be B or b and the last one can be G or g
The possible combinations we can get are:
EBG
EBg
EbG
Ebg
As there are 4 of them and they all have an equal chance of being the genotype, they all have an expected frequency of 25%

For the 2007 paper, question 22d, make sure you:
1) show the difference between genes and alleles by defining them both
2) make reference to the diagram as well

A sample answer could be:

Spoiler

Genes are sections of DNA that code for the production of a specific polypeptide (e.g the section of DNA that codes for B or b). Whereas, alleles are variations of genes (e.g. B and b are variations of a gene)

Hope this helps 

Thanks for your answer! For the 2007 one I was meant to write b) though, sorry.

[KT Nyunt]

Thanks for your answer! For the 2007 one I was meant to write b) though, sorry.

Sorry it took me a while to get back to you!
So for b)... I took a screenshot of the cell in the question. We see the the homologous chromosomes are separated and drawn to opposite sites of the cell by the spindles (as indicated by the dotted lines). So then after the first meiotic division, one cell will have the two chromosomes on the left of the picture and the other cell will have the two chromosomes on the right.

Then, we know in the process of meiosis, there's a second meiotic division, where we end up with 4 daughter cells. So for one cell, we separate it into 2 gametes.
The gametes that can come from cell with the chromosomes on the left are:

Spoiler

A B E D
A b E D

and we do the same for other cell:

Spoiler

a B e d
a b e d

Remember each gamete must have one of each gene (ie. the gene that codes for A or a, the gene that codes for B or b etc.)
Hope this helps 

[amelia20181]

is it possible to learn the whole syllabus in 2 weeks and get a good mark and how??