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July 16, 2019, 10:20:09 am

Author Topic: VCE Biology Question Thread  (Read 1259254 times)  Share 

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areeb008

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Re: VCE Biology Question Thread
« Reply #9615 on: October 30, 2017, 09:36:05 pm »
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hey guys, could someone clarify the main difference between accuracy and validity? also if an experiment is accurate is it necessarily valid as well and vice versa??

PhoenixxFire

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Re: VCE Biology Question Thread
« Reply #9616 on: October 30, 2017, 10:26:00 pm »
+1
hey guys, could someone clarify the main difference between accuracy and validity? also if an experiment is accurate is it necessarily valid as well and vice versa??
Accuracy is whether you are correctly measuring something. ie if you measure something that is actually 1metre and get 50cm your measurements (and therefore results) are not accurate. Validity is whether you are actually testing what you're supposed to be testing ie have you designed an experiment that tests your hypothesis?
No, a test can be accurate (measured correctly) but not valid (not testing the hypothesis) and vice versa.
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areeb008

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Re: VCE Biology Question Thread
« Reply #9617 on: October 30, 2017, 10:28:09 pm »
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Accuracy is whether you are correctly measuring something. ie if you measure something that is actually 1metre and get 50cm your measurements (and therefore results) are not accurate. Validity is whether you are actually testing what you're supposed to be testing ie have you designed an experiment that tests your hypothesis?
No, a test can be accurate (measured correctly) but not valid (not testing the hypothesis) and vice versa.

thanks g

Seno72

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Re: VCE Biology Question Thread
« Reply #9618 on: October 30, 2017, 11:14:22 pm »
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Do we need to nonsense and missense mutations?
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PhoenixxFire

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Re: VCE Biology Question Thread
« Reply #9619 on: October 30, 2017, 11:23:11 pm »
+2
Do we need to nonsense and missense mutations?
Yes.
Nonsense-codes for a premature STOP codon.
Missense-codes for a different amino acid.
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ezferns

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Re: VCE Biology Question Thread
« Reply #9620 on: October 30, 2017, 11:33:56 pm »
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How do phagocytes distinguish between self and non self? Do they have both self and non self antigen receptors or is there just self receptors and everything that doesn't fit is considered nonself?

PhoenixxFire

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Re: VCE Biology Question Thread
« Reply #9621 on: October 30, 2017, 11:36:31 pm »
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How do phagocytes distinguish between self and non self? Do they have both self and non self antigen receptors or is there just self receptors and everything that doesn't fit is considered nonself?
That is outside the study design. If you're asking out of curiosity Vox might be able to explain it.
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pink sharpie

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Re: VCE Biology Question Thread
« Reply #9622 on: October 31, 2017, 02:20:52 am »
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what key features of hominin evolution do we have to know? Like for morphological structures such as large cranial capacity and what not.
I'm having a difficult time remembering the features that have evolved as a result of bipedalism such as the pelvis structure as when I look these up they get really specific with names such as the iliac ala and gluteus medius which i've never seen in my text book!

PhoenixxFire

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Re: VCE Biology Question Thread
« Reply #9623 on: October 31, 2017, 08:16:53 am »
+1
what key features of hominin evolution do we have to know? Like for morphological structures such as large cranial capacity and what not.
I'm having a difficult time remembering the features that have evolved as a result of bipedalism such as the pelvis structure as when I look these up they get really specific with names such as the iliac ala and gluteus medius which i've never seen in my text book!
Increased cranium volume
Changed position of the forunem magnum
Increased width and decreased length of the pelvis

These pelvis changes did not evolve as a result of bipedalism, they evolved along side it. It was these changes (and others) that allowed us to become bipedal.
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dimenc

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Re: VCE Biology Question Thread
« Reply #9624 on: October 31, 2017, 09:10:27 am »
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Hi Everyone- sorry for all the questions
But am i right in saying;

APCs present MHC II which can be recognized by a Th
B cells present MHC II which can be recognized by a Th
Virally effected cells present MHC I which can be recognized by a Tc

Thanks!


PhoenixxFire

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Re: VCE Biology Question Thread
« Reply #9625 on: October 31, 2017, 09:20:55 am »
+1
Hi Everyone- sorry for all the questions
But am i right in saying;

APCs present MHC II which can be recognized by a Th
B cells present MHC II which can be recognized by a Th
Virally effected cells present MHC I which can be recognized by a Tc

Thanks!
APC's present peptide fragments (from molecules they have engulfed) on MHC2 which can be recognised by Th cells
I'm not sure what B cells present their bound antigen on to Th cells (I assume you mean to cause the Th cell to release cytokines) but we do not need to know that level of detail
Virally affected cells present peptide fragments (that they have produced) on MHC1 molecules to Tc cells.
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dimenc

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Re: VCE Biology Question Thread
« Reply #9626 on: October 31, 2017, 09:56:56 am »
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APC's present peptide fragments (from molecules they have engulfed) on MHC2 which can be recognised by Th cells
I'm not sure what B cells present their bound antigen on to Th cells (I assume you mean to cause the Th cell to release cytokines) but we do not need to know that level of detail
Virally affected cells present peptide fragments (that they have produced) on MHC1 molecules to Tc cells.

Okay thank you, would you say this is sufficient for the process of Cell Mediated Immunity?

- An APC presenting cell, such as a Dendritic cell, presents peptide fragments from a molecule they have engulfed on their MHC II molecules
- A Th cell binds to this antigen, which causes it to proliferate. The Th cell also releases cytokines which recruit other cells but also further proliferate the t cells into other cells such as Cytotoxic T cells, Regulatory T cells, T memory cells etc.
- Cytotoxic T cells roam the body searching for virally affected cells.
- One the Tc recognizes the peptide fragments on the MHC 1 marker of the cell, it binds and releases a granzyme called preforin
- Preforin punches holes in the virally affected cell, triggering apoptosis which ultiamtely, leads to the death of the cell. Any remains are quickly adsorbed by phagocytes.

- Th cells also can bind to death receptors on a cells surface using Fas signalling molecule and initiate apoptosis that way

PhoenixxFire

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Re: VCE Biology Question Thread
« Reply #9627 on: October 31, 2017, 10:17:36 am »
+3
- An APC presenting cell
I doubt you would get marked down for this but you wrote 'An Antigen Presenting Cell presenting cell' - It implies you don't know what APC stands for.
- A Th cell binds to this antigen, which causes it to proliferate. The Th cell also releases cytokines which recruit other cells but also further proliferate the t cells into other cells such as Cytotoxic T cells, Regulatory T cells, T memory cells etc.
This seems to be a common misconception. T cells do not differentiate into helper T cells and cytotoxic T cells. Both are already present in your body (Th cells in lymph nodes and Tc cells throughout your body) Tc cells are constantly attempting to bind to peptide fragments presented on MHC2. If they are selected (bind their antigen) they will not divide and differentiate without cytokines present but they are otherwise independent to Th cells. (Th and Tc cells both mature in the thymus gland - when they exit they are already one or the other.)

The cytokines released by Th cells cause ( already selected Tc cells to divide and differentiate into activated and memory Tc cells, (and Th cells to divide and differentiate into activated Th cells and memory Th cells, and B cells into memory B cells and Plasma B cells)

Tc cells searching for and binding their antigen happens at the same time as Th cells being presented with their antigen - not afterwards.

Try writing another one that shows that and i'll give it a read.
« Last Edit: October 31, 2017, 10:28:18 am by PhoenixxFire »
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dimenc

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Re: VCE Biology Question Thread
« Reply #9628 on: October 31, 2017, 10:56:52 am »
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I doubt you would get marked down for this but you wrote 'An Antigen Presenting Cell presenting cell' - It implies you don't know what APC stands for.This seems to be a common misconception. T cells do not differentiate into helper T cells and cytotoxic T cells. Both are already present in your body (Th cells in lymph nodes and Tc cells throughout your body) Tc cells are constantly attempting to bind to peptide fragments presented on MHC2. If they are selected (bind their antigen) they will not divide and differentiate without cytokines present but they are otherwise independent to Th cells. (Th and Tc cells both mature in the thymus gland - when they exit they are already one or the other.)

The cytokines released by Th cells cause ( already selected Tc cells to divide and differentiate into activated and memory Tc cells, (and Th cells to divide and differentiate into activated Th cells and memory Th cells, and B cells into memory B cells and Plasma B cells)

Tc cells searching for and binding their antigen happens at the same time as Th cells being presented with their antigen - not afterwards.

Try writing another one that shows that and i'll give it a read.

- Sorry that first part was just a mistake
- I am sort of confused at what you are saying so do th cells proliferate at all and how do they do it?
- So after a Th binds to the MHC 11 of an APC, what happens because now i am so confused

vox nihili

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Re: VCE Biology Question Thread
« Reply #9629 on: October 31, 2017, 11:43:09 am »
+4
How do phagocytes distinguish between self and non self? Do they have both self and non self antigen receptors or is there just self receptors and everything that doesn't fit is considered nonself?
That is outside the study design. If you're asking out of curiosity Vox might be able to explain it.

Outside of the study design, keep scrolling if you're not interested

It's surprisingly simple. Cells of the innate immune system, including phagocytes, have receptors that are able to recognise molecules that you only find in pathogens. These molecules are ones that, for whatever reason, appear to be shared by a broad range of pathogens. One such example is lipopolysaccharide, which is found in the cell walls of many bacteria. This is good for distinguishing self from non-self, as we don't have cell walls and therefore no lipopolysaccharide. These molecules are collective called pathogen-associated molecular patterns and are recognised by receptors called pathogen recognition receptors.
When these receptors are engaged, an immune response happens.

It's probably worth noting at this point, and of relevance to the VCE course, that the immune system doesn't really have "self" receptors. The immune system only needs to respond to non-self, so a way of distinguishing between the two is to just have receptors that always respond to non-self. There's no need to have self-receptors, because by having receptors capable of only responding to non-self, you already satisfy the requirement that the immune system distinguish between the two.
A way of looking at it is to say that I'm asking you to sort fruit. Let's say I want you to sort fruit into apples and non-apples. There are two ways I could do this. I could teach you all of the different types of fruit in the world, so that you can accurately say "this is a raspberry" and put it into the non-apple pile. This would, however, take a very long time for me to do; there are lots of fruit. Another way I could do this is to simply teach you what an apple looks like, and tell you that anything that doesn't look like this should go into the non-apple pile. That way, we achieve the same result, but without all the bother of teaching you to identify the fruit. This is, in essence, how the immune system works. Rather than teaching it what self is, just teach it what non-self is and then anything else that pops up is just self and thus, it can be ignored by the immune system.

Last thing to mention on this topic is that phagocytosis is mediated by complement and antibodies. Both help make bacteria (et al.) more tasty for phagocytes. So another way they can identify non-self is to have the adaptive immune system (via antibodies) do it for them :)
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