VCE Biology Question Thread

[Bruzzix]

What are selective pressures and selective agents and what is the difference between the two?

[grindr]

Just a clarification on the 'Parallel Evolution' theory: SO

Homo erectus moved out from Africa to other continents where they all evolved into homo sapiens?

Sounds dodgy...

The other hypothesis, 'Out of Africa' is more likely to be correct, right?

[chemzy]

Hello cosine

I found an answer to your question. Well, enzymes in organisms cannot synthesise DNA primers but they can make RNA primers, so they use them for natural processes such as DNA replication. But with pcr, since, it's an artificial process, we can make DNA primers in the lab and use them.

It's just a matter of whether or not our enzymes can make DNA primers or not. If they can't, alternative is RNA primers,

 

[cosine]

Why would the second response to a bee sting be more dangerous than the first reaction?

[Sine]

Why would the second response to a bee sting be more dangerous than the first reaction?

The initial response would produce antibodies which attach onto mast cells which is called desensitization(dont need to know this term for VCE) the second response will result in the allergen bind to the antibodies on mast cells subsequently releasing histamine, large quantities may cause anaphylactic shock.

[cosine]

Would it be reasonable to say, that because the antibodies come from B cells, that memory B cells are also produced during the first response, and these memory B cells over-produce IgE anitbodies upon the second detection at a much greater rate?

[mahler004]

However, I still do not get why during PCR, DNA primers are added and not RNA primers?

Hello cosine

I found an answer to your question. Well, enzymes in organisms cannot synthesise DNA primers but they can make RNA primers, so they use them for natural processes such as DNA replication. But with pcr, since, it's an artificial process, we can make DNA primers in the lab and use them.

It's just a matter of whether or not our enzymes can make DNA primers or not. If they can't, alternative is RNA primers,

 

Main reason is because RNA is very unstable - DNA is very stable so can be easily manipulated and stored. This is not the case for RNA.

[vox nihili]

Hello cosine

I found an answer to your question. Well, enzymes in organisms cannot synthesise DNA primers but they can make RNA primers, so they use them for natural processes such as DNA replication. But with pcr, since, it's an artificial process, we can make DNA primers in the lab and use them.

It's just a matter of whether or not our enzymes can make DNA primers or not. If they can't, alternative is RNA primers,

 

Just to add to this: if we had DNA primers, what would be the point of the primer in the first place? We need a primer because DNA polymerase can only extend strands, not make new ones. But if we had an enzyme in the cell that could make a DNA primer (i.e. make a new DNA strand from scratch), why wouldn't the cell just use that enzyme to make the full stand?

In PCR we can use DNA primers because we can synthesise them in the lab. Using DNA primers is much better, because it means that we don't need to add any enzymes to remove the RNA from the strand and replace it with DNA (as we do in DNA replication).

EDIT: what mahler004 said too. RNA is shit to work with.

[Bruzzix]

What are selective pressures and selective agents and what is the difference between the two?

Anyone?

[cosine]

Would it be reasonable to say, that because the antibodies come from B cells, that memory B cells are also produced during the first response, and these memory B cells over-produce IgE anitbodies upon the second detection at a much greater rate?

Mr T-Rav please enlighten me this was on my practice exam today

[cosine]

why is the answer NOT D?

Bumb

[cosine]

The answer is via the bloodstream. Dont only endocrine hormones travel via the bloodstream? I just got confused because we don't get told that this was released by an endocrine gland. Or are all glands endocrine glands??

[heids]

What are selective pressures and selective agents and what is the difference between the two?

A selection pressure is a factor in an organism's environment that removes unsuited individuals (VCAA), and a selective agent is basically the same, it's any agent of any sort that removes unsuited individuals.  They may be slightly different, but I don't think so.

why is the answer NOT D?

A person with blood group A is receiving AB - this person has antibodies against B proteins.  Thus when they receive blood with both the A and B proteins, they'll make antibodies against the B proteins.  (Yes, this is a tricky question that takes careful thought).

The answer is via the bloodstream. Dont only endocrine hormones travel via the bloodstream? I just got confused because we don't get told that this was released by an endocrine gland. Or are all glands endocrine glands??

Think about it - it's going from the pituitary (in the brain) to the thyroid, which it says is in the throat, so it's obviously travelling a reasonable distance --> thus it must be travelling in the bloodstream.

[Bruzzix]

why is the answer NOT D?

Bumb

Think of the bloodtypes as antigens on the surface of the red blood cell. Blood group A has the A type antigen, B has the B type antigen, AB has both and O has no antigens.
The blood will only be accepted if it doesn't have non-self antigens.

If group A received blood from group B there would be a non-self antigen introduced to the body and thus the body would reject it.
If group B received blood from group O, no non-self antigens are introduced to the body and the blood will be accepted. This applies for when group O donates blood to anyone - no blood type can reject it, hence why group O is sometimes referred to as the universal blood donor.
If group O receives blood from group A then again, non-self antigens are introduced and the blood will be rejected.
If group A receives blood from group AB then A antigens are introduced which is okay, but so are B antigens which is not okay, they will be rejected.

Edit: bangali_lok got to it first

[cosine]

The answer is B, but if a group B person receives blood from a group O person, then the blood from group O has antibodies for A and B proteins, and the group B person has B proteins on its surface? So wouldnt that mean the antibodies from the plasma of the group O blood will neutralise the proteins on the group B blood ?