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March 28, 2024, 11:05:06 pm

Author Topic: VCE Biology Question Thread  (Read 3570461 times)  Share 

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TheBigC

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Re: VCE Biology Question Thread
« Reply #10680 on: September 24, 2018, 10:39:49 pm »
+1
When B-cells encounter an antigen, does the antigen bind to an antibody OR another receptor on the B-cell, before being engulfed and presented on the B-cell's MHC-II marker? Does the same thing apply to allergens?

(1) The antigen would bind to a membrane-bound immunoglobulin/ antibody (B cell receptor)...
(2) In the context of allergens, the antigen would bind to surface Immunoglobulins (IgE) on MAST CELLS (after they have been primed (during second or nth exposure))...
« Last Edit: September 24, 2018, 10:43:19 pm by TheBigC »

peachxmh

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Re: VCE Biology Question Thread
« Reply #10681 on: September 24, 2018, 10:45:22 pm »
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The antigen would bind to a membrane-bound immunoglobulin/ antibody (B cell receptor)... In the context of allergens, the antigen would bind to surface Immunoglobulins (IgE) on MAST CELLS (after they have been primed (second or nth exposure)).


Thanks for the explanation! For the second part about allergens I meant during the initial exposure to the allergen when the B-cell first produces IgE antibodies (sry I didn't make this clear enough haha) - does the allergen bind to an antibody (is it IgE or can it be IgG?) on the B-cell, causing it to be presented on the MHC-II marker before a T-Helper cell causes the B-cell to differentiate into plasma and memory cells?
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vox nihili

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Re: VCE Biology Question Thread
« Reply #10682 on: September 24, 2018, 10:56:43 pm »
+5
Thanks for the explanation! For the second part about allergens I meant during the initial exposure to the allergen when the B-cell first produces IgE antibodies (sry I didn't make this clear enough haha) - does the allergen bind to an antibody (is it IgE or can it be IgG?) on the B-cell, causing it to be presented on the MHC-II marker before a T-Helper cell causes the B-cell to differentiate into plasma and memory cells?

You're getting into details well beyond VCE here, so don't worry so much about the answer.

B-cell receptors are antibodies that are stuck in the membrane of a B-cell. They also buddy up with some other proteins that help them transmit their receptory signal into the cell. The particular type of antibody in this case is actually IgM (IgM exists outside the cell as a pentamer; however, as the B-cell receptor it is monomeric—if these words mean nothing to you, ignore them).
It does not matter what kind of antibody the B-cell eventually goes on to produce; its receptors will always be IgM. So in the case of allergens, the allergen will bind to the IgM B-cell receptor, which will prompt the B-cell to start producing IgE (the reasons for the choice of IgE here are complicated and well beyond the course).
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Azim.m

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VCE Biology Question Thread
« Reply #10683 on: September 27, 2018, 02:58:20 pm »
0
Why is the krebs cycle apart of aerobic respiration if it does not require oxygen?

Monkeymafia

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Re: VCE Biology Question Thread
« Reply #10684 on: September 27, 2018, 03:58:31 pm »
+1
Why is the krebs cycle apart of aerobic respiration if it does not require oxygen?

Here is just my logic (but someone else will explain better):
- without oxygen, NADH can't be converted back to NAD in ETC. So there is no NAD for Krebs cycle
- ATP has to be used to make more ATP, so if 32 net ATP isn't produced in ETC (as a result of no oxygen present), then there is less ATP to carry out specific reactions (such as Krebs Cycle)

Hopefully that's right.

PopcornTime

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Re: VCE Biology Question Thread
« Reply #10685 on: September 27, 2018, 04:00:25 pm »
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How can Homo Neanderthalensis and Homo Erectus interbreed if they are separate species? Is this an exception to the rule...

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Re: VCE Biology Question Thread
« Reply #10686 on: September 27, 2018, 04:21:07 pm »
+2
Here is just my logic (but someone else will explain better):
- without oxygen, NADH can't be converted back to NAD in ETC. So there is no NAD for Krebs cycle
- ATP has to be used to make more ATP, so if 32 net ATP isn't produced in ETC (as a result of no oxygen present), then there is less ATP to carry out specific reactions (such as Krebs Cycle)

Hopefully that's right.


Ok, so the order of the reactions is:
-Glycolysis
-Kreb's Cycle
-Electron Transport Chain

In Glycolysis, we don't need oxygen. However, for the pyruvates to move into the mitochondria, the presence of oxygen is required. So, even though the later 2 reactions might not directly need oxygen, the cell needs to have oxygen for the reactions to continue.

Hopefully that makes sense.  :)

How can Homo Neanderthalensis and Homo Erectus interbreed if they are separate species? Is this an exception to the rule...


hmmm... my guess is that these species can only interbreed to produce infertile offspring? I know that this happens with mules, not sure if the same applies to humans  :P

However, if this above assumption is indeed correct, it would not be 'an exception the rule' provided that the offspring are infertile, meaning they themselves cannot reproduce. 

Not sure about this though.
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PhoenixxFire

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Re: VCE Biology Question Thread
« Reply #10687 on: September 27, 2018, 04:22:39 pm »
+2
How can Homo Neanderthalensis and Homo Erectus interbreed if they are separate species? Is this an exception to the rule...
There’s lots of exceptions to our definition of a species. For example, how do you define a species if it reproduces asexually? Some people use exceptions like if it’s only males of one species and females of the other that can interbreed (and not vice versa) then they’re seperate species, but until there’s a better definition of what a species is, just accept that they are seperate despite them not fitting the definition.
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Sine

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Re: VCE Biology Question Thread
« Reply #10688 on: September 27, 2018, 04:33:26 pm »
+1
How can Homo Neanderthalensis and Homo Erectus interbreed if they are separate species? Is this an exception to the rule...
I'm not 100% sure which "species" could interbreed but the "strict" definition for a species we take in VCE biology is that if two organisms can interbreed and produce a fertile, viable offspring they are the same species. Plenty of different species (e.g. lion and tiger) can interbreed and produce offspring (Liger, Tigon) but the offspring are not fertile.

But it's important to know that these are the arbitrary rules we have chosen to define a species so taking a strict definition may mean they are the same species. (VCAA 2015 Question 10 discusses this a bit for H. sapiens and H. neanderthalensis).

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Re: VCE Biology Question Thread
« Reply #10689 on: September 27, 2018, 05:36:07 pm »
0
The secondary immune response is normally more rapid and greater than the primary response - is this the same with allergic responses, comparing the initial sensitisation to the allergen and subsequent exposure?
Thank you
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darkz

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Re: VCE Biology Question Thread
« Reply #10690 on: September 27, 2018, 06:44:45 pm »
+4
The secondary immune response is normally more rapid and greater than the primary response - is this the same with allergic responses, comparing the initial sensitisation to the allergen and subsequent exposure?
Thank you

Yes that is correct. However in this case, it is important to note that sensitisation essentially 'primes' the mast cells - so the antibodies bind to the mast cells. Therefore, I believe the initial reaction is pretty much non-existant or mild at best
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peachxmh

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Re: VCE Biology Question Thread
« Reply #10691 on: September 28, 2018, 02:27:09 pm »
0
Can someone please provide worked solutions for this question? I'm really stuck haha - the solution is C

The carbon-14 content in bone is about one 12C atom to every 10 billion 14C atoms. The half-life of 14C is about 5500 years. Using radioisotopic dating techniques, a fossilised bone was found to have 0.125 14C atoms to every 10 billion 12C atoms. The most accurate estimate of the absolute age of the bone would be:
A. 5500 years.
B. 55 000 years.
C. 16 500 years.
D. 11 000 years.
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vox nihili

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Re: VCE Biology Question Thread
« Reply #10692 on: September 28, 2018, 02:49:41 pm »
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Can someone please provide worked solutions for this question? I'm really stuck haha - the solution is C

The carbon-14 content in bone is about one 12C atom to every 10 billion 14C atoms. The half-life of 14C is about 5500 years. Using radioisotopic dating techniques, a fossilised bone was found to have 0.125 14C atoms to every 10 billion 12C atoms. The most accurate estimate of the absolute age of the bone would be:
A. 5500 years.
B. 55 000 years.
C. 16 500 years.
D. 11 000 years.

Are you sure that you've written out the question properly? Your ratio of 12C:14C in the first part of the question looks wrong.
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PopcornTime

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Re: VCE Biology Question Thread
« Reply #10693 on: September 28, 2018, 02:50:48 pm »
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Ok, so the order of the reactions is:
-Glycolysis
-Kreb's Cycle
-Electron Transport Chain

In Glycolysis, we don't need oxygen. However, for the pyruvates to move into the mitochondria, the presence of oxygen is required. So, even though the later 2 reactions might not directly need oxygen, the cell needs to have oxygen for the reactions to continue.

Hopefully that makes sense.  :)
 

hmmm... my guess is that these species can only interbreed to produce infertile offspring? I know that this happens with mules, not sure if the same applies to humans  :P

However, if this above assumption is indeed correct, it would not be 'an exception the rule' provided that the offspring are infertile, meaning they themselves cannot reproduce. 

Not sure about this though.

Why is oxygen required for pyruvate to move into the mitochondria?

vox nihili

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Re: VCE Biology Question Thread
« Reply #10694 on: September 28, 2018, 02:54:28 pm »
+2
Why is oxygen required for pyruvate to move into the mitochondria?

Apologies to any Chem students reading this explanation, but a simple way to think about it is that the reactions that occur in the mitochondria eventually lead to the electron transport chain.
Kreb's produces all of your loaded carriers (i.e. NADH, FADH2) which then go to the ETC, offloading electrons and hydrogen ions. Those electrons are then "accepted" by oxygen, which takes them away.

If there weren't oxygen, then the electrons inthe ETC would have nowhere to go. If the electrons have nowhere to go, the ETC gets clogged up. If the ETC is clogged up, the carriers can't offload. If the carriers can't offload, you don't make any new NAD+. If there's no NAD+ Kreb's reactions can't occur. If Kreb's can't occur, then the pyruvate in the mitochondria doesn't get used. If the pyruvate doesn't get used, it builds up in the mitochondria. Once it's built up, the mitochondria stops bringing in more pyruvate (because it's already got too much).
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