VCE Biology Question Thread

[GodNifty]

By 'cellular response', I mean phagocytes and antigen presenting cells, so the 2nd line of defence. And by "humoral response", I mean complement proteins, cytokines, inflammation and fever, so in the 2nd line of defence also. There are cellular and humoral responses in the 3rd line of defence too, but they're different. And thanks for the clarification about the MHCs markers!!

You have to be careful here. Humoral response is not considered a 2nd line of defense.
The difference between 2nd and 3rd line is the specificity - 2nd line (innate) is not specific whereby the leukocytes and any other  target any foreign antigen. 3rd line is specific where, if the foreign antigen prevails and gets past the 2nd line, antibodies (from humoral response) specifically attack them. Complement proteins, cytokines, inflammation and fever can either be stimulated from the humoral immune response (hence specific) or can be innate, but humoral response is not classified in the 2nd line of defense.

The cellular response of the innate immune system can consist of phagocytes and antigen presenting cells. phagocytes can quickly eliminate PATHOGENS by engulfing them and breaking them down with digestive enzymes, and then releasing them out. but in another process,  phagocytosis of an ANTIGEN occurs, except it is followed by an class II MHC protein binding onto one of the fragments of the antigen and presenting it to a helper T cell......... how come the phagocytosis of a pathogen (first process i mentioned), doesn't involve MHC proteins? or similarly, why can't the second process not involve MHC proteins?

First process depends on the severity of the pathogen. If your first and second line of defense is losing the battle (best way I can put it), then it will signal the 3rd line of defense to create a more stronger defense. The 2nd process needs to involve MHC 2 proteins so that it can stimulate an inactive naive helper t cell to go through either humoral or cell mediated

[justinely]

You have to be careful here. Humoral response is not considered a 2nd line of defense.
The difference between 2nd and 3rd line is the specificity - 2nd line (innate) is not specific whereby the leukocytes and any other  target any foreign antigen. 3rd line is specific where, if the foreign antigen prevails and gets past the 2nd line, antibodies (from humoral response) specifically attack them. Complement proteins, cytokines, inflammation and fever can either be stimulated from the humoral immune response (hence specific) or can be innate, but humoral response is not classified in the 2nd line of defense.

First process depends on the severity of the pathogen. If your first and second line of defense is losing the battle (best way I can put it), then it will signal the 3rd line of defense to create a more stronger defense. The 2nd process needs to involve MHC 2 proteins so that it can stimulate an inactive naive helper t cell to go through either humoral or cell mediated

Thanks so much! My bio teachers taught me that humoral immunity is also part of the 2nd line of defence (non-specific), that's why. They also showed me this diagram below. Thanks for your clarification, I understand now. I will definitely ask my teachers about it.

[GodNifty]

Thanks so much! My bio teachers taught me that humoral immunity is also part of the 2nd line of defence (non-specific), that's why. They also showed me this diagram below. Thanks for your clarification, I understand now. I will definitely ask my teachers about it.

I guess I can kinda see the point of view from your teacher. Humoral is related to body fluids, but it's more so dealing with antibodies, which are specific.

[ABB0005]

Is it better doing VCAA exams first or company exams building up in difficulty to VCAA exams

[darkz]

Is it better doing VCAA exams first or company exams building up in difficulty to VCAA exams

Really depends on how much time you've got left and how prepared you are. If you've got loads of time left, then start with company papers to get used to the content. Then with VCAA, you should get a gauge of how they want things answered. Alternatively, you can start with old VCAA, then company, then recent VCAA.

[Erutepa]

Are the terms "MHC class I PROTEINS" and "MHC class I MARKERS" interchangeable? Do "proteins" and "markers" refer to the same thing? When do u use which?

You can refer to them as MHC markers, molecules, and proteins - either is fine.

You have to be careful here. Humoral response is not considered a 2nd line of defense.
The difference between 2nd and 3rd line is the specificity - 2nd line (innate) is not specific whereby the leukocytes and any other  target any foreign antigen. 3rd line is specific where, if the foreign antigen prevails and gets past the 2nd line, antibodies (from humoral response) specifically attack them. Complement proteins, cytokines, inflammation and fever can either be stimulated from the humoral immune response (hence specific) or can be innate, but humoral response is not classified in the 2nd line of defense.

Humoral immunity can infact contribute to this innate immune response/2nd line of defence. Humoral immunity by definition consists of any immune response mediated by molecules in extracellular fluids (i.e. antibodies in the 3rd line of defense and compliment proteins in the 2nd line of defense). This seems to be what you have been taught justinely. However, in terms of the VCE biology cource, VCAA do not use the term humoral immunity in this way - instead humoral immunity will is exclusively used to refer to the production of antibodies by B cells in the 3rd line of defense (as GodNifty explains).

The innate 2nd line of defence consists of Cellular Response and Humoral Response........ which one happens first?
Or do they happen at the same time?

As explained above, within the VCE biology course, we do not divide the innate immune system up into humoral responses (or cellular responses). Despite this, both of these responses would be occuring at the same time.

The cellular response of the innate immune system can consist of phagocytes and antigen presenting cells. phagocytes can quickly eliminate PATHOGENS by engulfing them and breaking them down with digestive enzymes, and then releasing them out. but in another process,  phagocytosis of an ANTIGEN occurs, except it is followed by an class II MHC protein binding onto one of the fragments of the antigen and presenting it to a helper T cell......... how come the phagocytosis of a pathogen (first process i mentioned), doesn't involve MHC proteins? or similarly, why can't the second process not involve MHC proteins?

APCs (like dendritic cells) will take up/obtain antigens engulfing pathogens (which contain/posess the antigen) or by engulfing debris that might consist of/contain the antigen. If this dendritic cell engulfs a pathogen (i.e. a bacteria) it will detroy the pathogen and may preserve its anitgens for presentation just as it would if it engulfed the antigen as debris. The cell will process this antigen and present fragments of it on its MHC II for activation of the adaptive immune response. As such, antigen presentation will occur in both cases you have described, not just when the antigen is engulfed as debris.
Hopefully this helps!

[Snow Leopard]

Sorry for the dumb question but: are things like anxiety and addictions examples of positive feedback loops?
- Also what stuff from 1/2 Bio, is also in 3/4 Bio?
Thanks in advance 

[s110820]

Hi Snow Leopard,

I'm pretty sure mental illnesses/disorders such as anxiety and addiction would be a negative feedback loop rather than a positive feedback loop as both are triggered by three overlapping events: the trigger or environmental cue, the mental reactivity and physical reactivity. Usually speaking and from personal experience, I find that my anxiety "loop" in a more physical/literal form reduces the change of my mindset, which thus when I studied this topic in biology, enabled me to understand that negative feedback reduces change whereas positive feedback amplified change (which will result in more of a certain product).

Hopefully, that helps

Have a great week and kind regards,

Darcy Dillon.

[darkz]

Just to confirm, so signalling molecules either combine to receptors inside the cell membrane or on it's surface? Some can bind to intracellular receptors in its nucleus and cytoplasm?

Correct, signalling molecules can either bind to extracellular receptors i.e. on the plasma membrane or intracellular receptors i.e. in the nucleus or cytosol.

[justinely]

You can refer to them as MHC markers, molecules, and proteins - either is fine.

Humoral immunity can infact contribute to this innate immune response/2nd line of defence. Humoral immunity by definition consists of any immune response mediated by molecules in extracellular fluids (i.e. antibodies in the 3rd line of defense and compliment proteins in the 2nd line of defense). This seems to be what you have been taught justinely. However, in terms of the VCE biology cource, VCAA do not use the term humoral immunity in this way - instead humoral immunity will is exclusively used to refer to the production of antibodies by B cells in the 3rd line of defense (as GodNifty explains).
As explained above, within the VCE biology course, we do not divide the innate immune system up into humoral responses (or cellular responses). Despite this, both of these responses would be occuring at the same time.
APCs (like dendritic cells) will take up/obtain antigens engulfing pathogens (which contain/posess the antigen) or by engulfing debris that might consist of/contain the antigen. If this dendritic cell engulfs a pathogen (i.e. a bacteria) it will detroy the pathogen and may preserve its anitgens for presentation just as it would if it engulfed the antigen as debris. The cell will process this antigen and present fragments of it on its MHC II for activation of the adaptive immune response. As such, antigen presentation will occur in both cases you have described, not just when the antigen is engulfed as debris.
Hopefully this helps!

wow, that helps a lot! thank you so much!!

[makram]

When looking at antibody count in the blood after vaccinations, why doesn't the count drop to zero?

Also for question 8 c. exam 1 2010, why is the antibody count in the baby above zero before the initial vaccine? (I deciphered this is because antibodies, through natural passive immunity, has reached the baby from the mother. But if the mother was only infected with measles as a child, why did she still have antibodies specific to measles after so many years?)

In Australia, vaccination against measles is a two-dose schedule. The first dose is generally given at age 12 months
and the second dose at 4 years.
c. On the grid below, graph the level of measles antibodies you would expect in a vaccinated child.
The child’s mother is known to have had measles as a child.

[whys]

When looking at antibody count in the blood after vaccinations, why doesn't the count drop to zero?

Also for question 8 c. exam 1 2010, why is the antibody count in the baby above zero before the initial vaccine? (I deciphered this is because antibodies, through natural passive immunity, has reached the baby from the mother. But if the mother was only infected with measles as a child, why did she still have antibodies specific to measles after so many years?)

I am assuming that in an ideal situation, the antibody count of the baby would be above zero for the reasons that you have outlined. Although the mother only had measles as a child, you probably need to assume that her immunological memory has been intact for a long time, although this probably isn't true in real life as immunity can diminish over time in many cases.

As the baby was exposed to two vaccinations, its immunological memory (prevalence of antibodies specific to measles and memory cells) won't fade anytime soon, although it is possible it could technically drop to zero in the far future if it is not exposed to measles again.

^This is my understanding of the immune system, feel free to correct me if I'm wrong

[vox nihili]

When looking at antibody count in the blood after vaccinations, why doesn't the count drop to zero?

Also for question 8 c. exam 1 2010, why is the antibody count in the baby above zero before the initial vaccine? (I deciphered this is because antibodies, through natural passive immunity, has reached the baby from the mother. But if the mother was only infected with measles as a child, why did she still have antibodies specific to measles after so many years?)

In Australia, vaccination against measles is a two-dose schedule. The first dose is generally given at age 12 months
and the second dose at 4 years.
c. On the grid below, graph the level of measles antibodies you would expect in a vaccinated child.
The child’s mother is known to have had measles as a child.

These are both really excellent questions. whys has given you an answer that is pretty close to the money, but I will clear up a couple of things.

whys is absolutely right in saying that immunity will theoretically drop to zero after some time. In the graph you've provided, it is dropping towards zero, but on both occasions a vaccine prevents it from doing so. This may help to explain why we vaccinate at these ages!
Theoretically, at the end of each year you are left with fewer B-cells specific to measles, so your immunity does wane over time. This is particularly the case for vaccine-induced immunity, which is far less robust than immunity that comes from having a disease.

Your second point is correct. The baby has immunity initially as it has acquired it from the mother. The antibodies cross the placenta and are with the baby from birth. Over time, these antibodies break down, so the baby gets more from the mother via breast milk. You suggested that the mother might not have immunity to measles, because it has been a long time since she has had the disease. whys was also unsure about whether the mother would actually have immunity in real life. The simple answer is that yes, she would! As I alluded to earlier, immunity acquired from getting a disease is a lot more robust (i.e. it lasts longer). So even though the mother had the disease as a child, you would expect that immunity to be with her until she dies.

[WhatisaMeMe]

Hi just a quick question:
Is a signal-protein complex formed inside the cell from hydrophobic signalling molecules considered a secondary messenger by its own? Thanks

[ErnieTheBirdi]

Hey everyone! I have an upcoming AOS2 SAC2 for Unit3 on immunity and all the signalling stuff. I still don't really understand it all, for example, naive and regular cells? Lymphatic system and MHC proteins? I was just wondering i someone would be able to explain those things to me? and if possible give me a guideline/checklist on what to look out for/study more of for the SAC (I know it's on the study design).