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March 29, 2024, 10:59:54 pm

Author Topic: VCE Biology Question Thread  (Read 3571694 times)  Share 

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Springyboy

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Re: VCE Biology Question Thread
« Reply #10485 on: June 20, 2018, 02:43:34 pm »
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Can someone confirm the following functions:

Glycolipids -- act as receptors for cellular recognition

Glycoproteins -- help cells to aggregate for tissue formation

Thanks.

That's correct with glycolipids, though they also maintain the stability of the cell membrane
From what I know glycoproteins do help cells aggregate for tissue formation, though they have many other functions as well

at918

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Re: VCE Biology Question Thread
« Reply #10486 on: June 20, 2018, 08:46:46 pm »
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HI everyone,
For this dot point in the study design:
-Significant changes in life forms in Earth’s geological history including the rise of multicellular organisms, animals on land, the first flowering plants and mammals.
Do we need to know the different theories (primordial soup theory, RNA world Theory) or do we just need to understand the geological time scale ?
Also, to what extent/ detail should we understand the geological time scale?

Thanks

peachxmh

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Re: VCE Biology Question Thread
« Reply #10487 on: June 20, 2018, 10:00:21 pm »
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Hi :) If I was required to graph the results of an experiment where the independent variable is not numerical (in this case it is the TYPE of antibiotic and the respective concentrations of each antibiotic are not given, so assuming they are the same), but the dependent variable is numerical, what type of graph would I use? Is it possible to use a scatter plot graph in this case or would it have to be a column graph (which from my knowledge is quite rare in Bio?)
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PhoenixxFire

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Re: VCE Biology Question Thread
« Reply #10488 on: June 20, 2018, 10:15:03 pm »
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Hi :) If I was required to graph the results of an experiment where the independent variable is not numerical (in this case it is the TYPE of antibiotic and the respective concentrations of each antibiotic are not given, so assuming they are the same), but the dependent variable is numerical, what type of graph would I use? Is it possible to use a scatter plot graph in this case or would it have to be a column graph (which from my knowledge is quite rare in Bio?)
Do you have a time variable or is it just a single number?
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peachxmh

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Re: VCE Biology Question Thread
« Reply #10489 on: June 20, 2018, 10:19:01 pm »
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Do you have a time variable or is it just a single number?

Well in the prac the independent variables are the different types of antibiotics and the dependent variables is the zone of inhibition in mm so for each antibiotic the result would be a single number, if that's what you mean? I wasn't given any other numbers other than the temperature of the incubator (for the agar plates containing bacteria on which the antibiotics are tested, to allow the bacteria to grow) which is the same for all experimental groups
« Last Edit: June 20, 2018, 10:20:52 pm by peachxmh »
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PhoenixxFire

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Re: VCE Biology Question Thread
« Reply #10490 on: June 21, 2018, 09:12:56 am »
+1
Well in the prac the independent variables are the different types of antibiotics and the dependent variables is the zone of inhibition in mm so for each antibiotic the result would be a single number, if that's what you mean? I wasn't given any other numbers other than the temperature of the incubator (for the agar plates containing bacteria on which the antibiotics are tested, to allow the bacteria to grow) which is the same for all experimental groups
Yeah I'm pretty sure you would have to use a bar chart for that.


HI everyone,
For this dot point in the study design:
-Significant changes in life forms in Earth’s geological history including the rise of multicellular organisms, animals on land, the first flowering plants and mammals.
Do we need to know the different theories (primordial soup theory, RNA world Theory) or do we just need to understand the geological time scale ?
Also, to what extent/ detail should we understand the geological time scale?

Thanks
We can't really be sure exactly what we need to know, but I doubt that you need to know the theories. Given it gives you examples of what events you need to know, just learn them and then generally understand the geological time scale, like how far apart events happened, that complex life developed very recently, etc. You should ask your teacher what they want you to know for your SAC though as they might have a different interpretation of that dot point.


Can someone confirm the following:

Mutations: increased genetic diversity
Chromosomal abnormalities: reduced genetic diversity
Environmental selection pressures: not too sure about this Decreased. Selection pressures cause a phenotype to be favoured, individuals with that phenotype will have a similar genotype, therefore the favoured individuals are genetically similar, making the population less diverse.
Gene flow: increased genetic diversity
Genetic Drift: reduced genetic diversity

When you're talking about genetic diversity it's important to read the context of the question. For example gene flow leads to increased diversity in a population but less diversity between populations.
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PopcornTime

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Re: VCE Biology Question Thread
« Reply #10491 on: June 22, 2018, 05:51:54 pm »
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Hi,

Can someone explain why the following answer is A and not C?

The action of neurotransmitters:
a) has a limited duration due to action of enzymes in the synaptic gap
b) ceases when the neurotransmitter is absorbed by the post-synaptic membrane
c) occurs only between neurons
d) is only excitatory

Also, what does excitatory mean in the context of neurotransmission?

Sine

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Re: VCE Biology Question Thread
« Reply #10492 on: June 22, 2018, 06:06:24 pm »
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Hi,

Can someone explain why the following answer is A and not C?

The action of neurotransmitters:
a) has a limited duration due to action of enzymes in the synaptic gap
b) ceases when the neurotransmitter is absorbed by the post-synaptic membrane
c) occurs only between neurons
d) is only excitatory

Also, what does excitatory mean in the context of neurotransmission?
neurotransmitters can act on stuff other than neurons such as effector muscles hence C is incorrect. Excitatory would mean to continue transmission of the electrical signal or to cause contraction.

TheBigC

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Re: VCE Biology Question Thread
« Reply #10493 on: June 22, 2018, 09:22:05 pm »
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Correct me if I'm wrong, but I thought that B or T cells are clonally selected after maturation and migration to the lymph node where they bind with an antigen and are then called 'selected' or 'activated' B & T cells and subsequently they undergo clonal expansion and they differentiate and proliferate? Or is that considered a part of the maturation process?

You are 100% correct. I made a significant typo - I meant to say "NEGATIVE and POSITIVE selection", not clonal, hence why I referred to 'self-tolerance' afterward... arghh... sorry - thanks for the correction - I'll edit it out.
« Last Edit: June 22, 2018, 09:24:34 pm by TheBigC »

TheBigC

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Re: VCE Biology Question Thread
« Reply #10494 on: June 22, 2018, 09:27:13 pm »
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He will probably have to qualify what he meant here because I’m not entirely sure. T and B cells mature in the thymus/bone marrow where they’re tested for self reactivity (and some weird things happen with their receptors) they end up with the correct receptor (either CD4 or CD8) and (hopefully) not react to self antigens. Then they’re mature and they enter general circulation. They’re called naive until they bind their antigen though (maybe that’s what TBC meant?) but they don’t get clonally selected until after they mature.


You are right Pheonixx. I made a typo - meant to say "NEGATIVE and POSITIVE selection", not clonal. Thanks for clarifying it for everybody whilst I was away from the Biology Question thread.

PopcornTime

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Re: VCE Biology Question Thread
« Reply #10495 on: June 23, 2018, 10:48:43 am »
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You are right Pheonixx. I made a typo - meant to say "NEGATIVE and POSITIVE selection", not clonal. Thanks for clarifying it for everybody whilst I was away from the Biology Question thread.

What exactly is negative and positive selection?

TheBigC

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Re: VCE Biology Question Thread
« Reply #10496 on: June 23, 2018, 01:21:58 pm »
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What exactly is negative and positive selection?

Negative selection, also known (in one form) as clonal deletion (VCE level), involves the elimination (via apoptosis) of self-reactive B cells and T cells of the immune system. This occurs within the Thymus for T cells and the Bone marrow for B cells. Ultimately, what occurs is that self-antigens are presented on the MHC of the cells in the bone marrow or thymus and if the respective B and T cells are reactive toward such (generate an immune response), they are eliminated (so as to not cause an autoimmune disease in the host).

Now, positive selection involves the recognition of non-self antigens presented and generation of an immune response. If an immune response is generated by the immune cell, it will not be eliminated, if not, the contrary will occur.

Ultimately, both B cells and T cells must undergo these tests in the primary lymphoid organs and "pass" (mostly*) to be considered naive and self-tolerant.

*cells that demonstrate a moderate affinity toward self-antigens still pass the negative selection process.
« Last Edit: June 23, 2018, 01:24:38 pm by TheBigC »

PopcornTime

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Re: VCE Biology Question Thread
« Reply #10497 on: June 23, 2018, 10:32:23 pm »
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So with the 3rd line of defence, t-helper cells signal to B cells, with B cell receptors specific to the antigen, to undergo clonal expansion. I have 2 questions about this:
- how do t helper cells secrete cytokines that target a specific B cell if there are many B cells around? Couldnt cytokines "accidentally" trigger diff and prolif of other neighbouring B cells
- also, antigens select B cells, but how does the immune system have so many varieties of different B cell receptors that can be specific to antigens?

PhoenixxFire

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Re: VCE Biology Question Thread
« Reply #10498 on: June 24, 2018, 09:21:06 am »
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So with the 3rd line of defence, t-helper cells signal to B cells, with B cell receptors specific to the antigen, to undergo clonal expansion. I have 2 questions about this:
- how do t helper cells secrete cytokines that target a specific B cell if there are many B cells around? Couldnt cytokines "accidentally" trigger diff and prolif of other neighbouring B cells
- also, antigens select B cells, but how does the immune system have so many varieties of different B cell receptors that can be specific to antigens?

Not VCE relevant

1. I don't really know the answer to this. Possibly through either contact-dependant signalling (but then how would it activate the Tc cell) or maybe it only activates cells that have already been selected.

2. I looked this up a bit - it's actually really cool!

So the antibody is made up of a constant region and a variable region. The variable region is the bit at the top where the binding sites are. The variability in the binding sites is due to random recombination of the gene segments that encode it, and mutations in that area of the antibody gene. The antibody variable region is polygenic - it's made up of 3 genes (V, D, J). It's also polymorphic - during antibody production one allele of each V, D, and J are chosen. They are then joined together using random genetic recombination which produces the variety in antibody binding sites.
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TheBigC

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Re: VCE Biology Question Thread
« Reply #10499 on: June 24, 2018, 12:45:47 pm »
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1. I don't really know the answer to this. Possibly through either contact-dependant signalling (but then how would it activate the Tc cell) or maybe it only activates cells that have already been selected.

Tc cells, in order to activate selected B cells, must bind to the presenting B cell's MHC II and THEN secrete cytokines (i.e. interleukin-2 (if I am not mistaken)). Thus, it will only activate the one B cell which is selected as a two-step "verification" process must occur.

Note: Tc cells are activated by the B cell's antigen presentation and the release of 'costimulatory' cytokines (by the B cell).
« Last Edit: June 24, 2018, 12:50:42 pm by TheBigC »