VCE Biology Questions Thread

HKS

Laila
Hi Laila, i think its because it is a flu virus and this is transmitted via air droplets, so the flu will enter the nose by 0inhaling the air particles or either thru contaminated food or water so stomach acid. and therefore intact skin would not be an appropriate answer for a question like this.

Laila

HKS Thank you so much 🙂

HKS

All good🙂

Taaaa76

I need help with this question:

A scientist wishes to make a recombinant plasmid into which they are going to insert gene X.
(I summarised what's Important from the table they showed):
EcoRI (sticky ends)
HindIII (sticky ends)
BamHI (sticky ends)
BalI (blunt ends)
HaelI (blunt ends)
SmaI (blunt ends)
The best option to do this is to
A. use BamHI to cut around the gene and through the plasmid.
B. cut around gene X with SmaI and cut the plasmid with SmaI.
C. cut around gene X with EcoRI and cut the plasmid with BamHI.
D. cut around gene X with HaeIII and cut the plasmid with HindIII.

The answer is A but I don't understand how. Can someone explain?

_sophiestudies_

Taaaa76 Remember that recombination works best with sticky end restriction endonucleases. This is because they create a specific overhang in the gene that can match the overhang created in the plasmid (blunt ends aren't specific enough, and any nucleotides could insert themselves. There's no hydrogen bonding between the complementary nucleotide overhangs to stabilize the formation of the vector/insert structure (i.e. the overhangs of the gene and plasmid can form hydrogen bonds, whereas that doesn't work with blunt ends). Therefore, B and D are incorrect (they're blunt end restriction endonucleases). C isn't correct either because you need to use the same restriction endonuclease for both the gene and plasmid, as they'll make a cut at the same base code (means they'll be complementary and can bind). A is correct because BamHI is a sticky end restriction endonuclease and is used to cut around the gene and through the plasmid (used for both).

Taaaa76

I need help with another question:
Which one of the following is a correct statement about monoclonal antibodies?
A. They facilitate a specific immune response.
B. They provide protection against a wide variety of pathogens.
C. They can help reduce swelling caused by rheumatoid arthritis.
D. They are produced by the cells of organisms that have strong immune systems.

The answer is C but I don't understand how

_sophiestudies_

Taaaa76 The answer is C because monoclonal antibodies can target auto-immune diseases, such as rheumatoid arthritis by supressing the immune system's attack on its own cells (i.e. supresses action of auto-reactive immune cells). They don't actually initiate an immune response (A), protect you against pathogens like vaccinations or types of disease control methods (B) or are produced by cells of an organism with a strong immune system (D -> they're produce from B cells in mice and myeloma cells).

Taaaa76

I need help with yet another question:

Many laboratories around the world have been sequencing influenza viruses since the 1980s. The results are available in databases so that researchers can compare genetic sequences in a process called genetic characterisation. Which one of the following would a researcher be interested in if their aim is to control the emergence of a new strain of virus that can infect humans?
A. if a current virus has caused infections in the past
B. the extent of genetic similarity between different strains
C. how effective vaccines are against different strains of virus
D. genetic changes in viruses that circulate in animal populations

The answer is D and the explanation is :The aim of studying the viruses is to attempt to control the emergence of new strains. This can only be accomplished by monitoring genetic changes.
It doesn't make sense??

Taaaa76

_sophiestudies_ I understand that they do not initiate the specific immune response, but they do help with it right? When the question says facilitate do they mean the antibodies start it or help it>

_sophiestudies_

Taaaa76 They don't facilitate, they activate or supress. It is kind of confusing, and in a way, it's somewhat correct because they play a role in it, but C is the most correct.

Taaaa76

_sophiestudies_ I still don't understand why it needs to be same restriction enzyme.
And I don't understand another thing: why does it need to make two cuts? one through the gene and through the plasmid? Can't it just cut at one point, end up with two ends and then the gene can bind there?

Taaaa76

_sophiestudies_
So monoclonal antibodies suppress or activate the specific immune response?

_sophiestudies_

Taaaa76 yes. They specifically supress or activate a specific immune response, depending on the application. They're not the same as regular antibodies. This MCQ answer is correct to a degree, but not specific enough compared to answer C.

_sophiestudies_

Taaaa76 Restriction enzymes all make cuts at different DNA sequences. It ensures the cuts made in the gene and the plasmid match and can bind via complementary base pairing. Also, it doesn't make two cuts. It makes one cut in the plasmid, creating an opening for the gene, and two cuts in the gene (basically at either end of the gene to ensure the hanging indents will be able to bind with those on the plasmid).

Taaaa76

_sophiestudies_
_sophiestudies_
Ohhh I understand now. Thanks for explaining!

abbey1234321

Barnacles are attached to rocks and cannot travel to avoid natural disasters or to mate with other barnacle populations.
A heatwave in a small coastal town led to the dark barnacles along the shoreline dying off. The lighter-grey barnacles were more likely to survive and now, the population is mostly comprised of light-grey barnacles.
Question 19
What occurred in this population?
A. natural selection
B. gene flow
C. bottleneck effect
D. viral drift

can someone please help me with this question? I though that this would be natural selection but the answer is C and im not sure why? I thought that light grey barnacles was a selective advantage?
Thanks!

Lam005

abbey1234321
The answer is C because the bottleneck effect is usually attributed to a natural disaster occurring which leaves a small unrepresentative sample alive. Here, the natural disaster is the heatwave which has killed many of the barnacles. Of those surviving, a large proportion of the barnacles would possess alleles for a light grey colour (this is what I mean by an unrepresentative sample. The original pre-heatwave barnacles population would not have such a high proportion of individuals with alleles for light grey). I don't think you're too incorrect but you're making a big assumption in that light grey barnacles was a selective advantage. I don't think anywhere in the question stem it mentions that it is a selective advantage nor does it mention any selection pressures which you can then infer a selective advantage from. Overall, answer C is a better option which is slightly more difficult to fault. 🙂

Taaaa76

Lam005
“ lighter-grey barnacles were more likely to survive”
Doesn’t this mean the lighter barnacles have a selective advantage?

_sophiestudies_

Taaaa76 they would have a selective advantage, since they more likely to survive. However, because a random event has occurred (i.e. heatwave) and has reduced the genetic diversity of the population, the bottleneck effect/C makes the most sense. Yes, natural selection is almost always going to be present, but in this case, it's not the main thing that has occurred. Often with exam style questions, there is a somewhat right answer (i.e. A) but also a more correct answer (i.e. C). Hope that helps!

abbey1234321

_sophiestudies_
So if it was a predator that came and ate all of the darker barnacles and the grey ones survived it would be natural selection. But since it was a natural disaster (heatwave) that has changed the gene pool then the bottleneck effect is specifically what is happening?

_sophiestudies_

abbey1234321 yes that's correct.

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