VCE Biology Questions Thread

S007

For Past exam 2022 question 21 why is multiple choice C is wrong and why is D right like I feel both of them are right

lune777

Hi I'm a bit confused with something I found in a discussion:
Q: Why is it that once a virus mutates, it isn't recognised by antibodies?
A: Selection pressures related to it are different. Heamoglutanin and neurominadase help it to enter and leave cells due to antigens and surface proteins - allowing it to go undetected by the immune system.
Do we need to know about anything in the above answer?

S007

lune777 so answering the first question from what I have from my knowledge so far there's two different types of mutations Antigenic drift and antigenic shift. so for antigenic shift imagine someone is vaccinated for lets say a type of covid strain and there also vaccinated for chickenpox (rlly random) but if those two viruses infect the same host cell (cell in the organism) there a high chance of the two viruses mixing together and basically making a completely new strain now if that happens new antibodies are needed to fight the complete new combination of the two DESPITE the fact that u have been vaccinated for both. and basically a new vaccine is also needed

lune777

Also for selective breeding, what does it mean by: you might be inadvertently selecting for an undesirable trait when you’re selecting for certain traits, which is unfavourable for survival.

S007

lune777 scientists, researches do make mistakes so they can accidently mess up sometimes and so choose unfavourable traits

lune777

S007
yep this makes sense - i'm just a bit confused about why they were talking about selection pressures and HN proteins.
I think they're possibly talking more about antigenic drift occurring (changing Hemagglutinin and neuraminidase) due to viruses with unique proteins that can evade the immune system possibly being selected for, making them more likely to reproduce?
Could someone please check this in case it's wrong cos I'm legit just guessing atp lmao

lune777

S007 ohhh so is this kinda like even though they're selecting for a favourable phenotype, another unfavourable one is also being selected for kinda by accident, that's not better for survival

S007

Hope that helped

S007

lune777 honestly i think the answer they gave it might make you confused so don't worry too much abt it. They do like for some reason using influenza virus in exams because they undergo antigenic drift quite often you don't have to memorise anything abt influenza you just have to know the overall concept such as antigenic shift and drift and be able to apply it in different questions and different examples. Q6 from the 2022 exam there's a question related to influenza and it undergoing antigenic drift so try doing that since it'll be helpful just for practice.

S007

lune777 no its not better for survival. That's why they have to find new solutions when mistakes like accidentally choosing an unfavorable trait do occur. An analogy for this could be that someone is trying to fix his car or smth he fixed a part of it but then realized he broke another part of the car so now he has to fix that.

sarah99

Hi, just wondering, do plants take in both O2 and CO2 from their environment? I know they release O2 from photosynthesis, but they also need to take in O2 for cellular respiration right? Or do they just use the O2 released from photosynthesis?

S007

sarah99 so plants undergo both cellular respiration and photosynthesis. In photosynthesis, they take in CO2 in the second stage so the Independent stage and then the co2 undergoes carbon fixation and as a result glucose is produced. They also take out oxygen in the light-dependent stage of photosynthesis. Whereas in cellular respiration (aerobic respiration) plants take in oxygen and release carbon dioxide (just like us) and eventually make ATP. I hope that helped.

sarah99

S007 Yeahhhhh but does the input of CO2 and O2 for the respective processes need to come from the environment? And accordingly they are released into the environment? Like O2 from photosynthesis can't be used as an input for cellular respiration etc. so that means plants take in O2 right - cos i always thought they only take in CO2!!

lune777

S007 yepp makes sense - similar to like selective breeding dogs like pug faces that aren't better for their breathing ig

lune777

S007 okay cool thanks!! yeah my school was going a bit deep into it that's why - i doubt VCAA would ask us stuff like that

eve

hi im new here!!

just a quick question do we need to remember what crispr stands for??

S007

i think its good to remember

S007

lune777 yeahh its not good for there breathing 😢

S007

sarah99 it doesnt always have to happen naturally I mean scientist and researches or anyone really do experiments relating to this stuff so like people can conduct experiments for plants and give it like a specific amount of O2 or CO2 just to measure the rate of cellular respiration or photosynthesis and look at what exactly is happening. BUT NATRUALLY like plants that are not put in experiments yes they need CO2 and O2 from the environment to survive. and yes they do release O2 from photosynthesis to the environment OR they can use it for cellular respiration and they also release CO2 from cellular respiration into the environment BUT they can also use it for photosynthesis. and YES plants take in O2 just like us to eventually produce ATP and they also take in CO2 to produce glucose.

sarah47

hi, just had a question about the trp operon. So there's a question that asks for the impact of a nonsense mutation in the trpR gene. The answer says that there would be continuous production of tryptophan. But wouldn't attenuation still occur to prevent transcription completion and limit trp production?

Novahkiin

sarah47 according to the answer it seems that mechanisms of attenuation are not considered for this question. Thus, I'd say that you're only required to answer based on the impact of the nonsense mutation on the trpR gene, being that a functional repressor protein would not be able to be produced, and therefore tryptophan production would occur indefinitely. While trp operon attenuation is a part of the 3/4 bio course, I haven't come across any questions that assess trp operon attenuation, such questions only assess trp operon repression. There may be some questions about attenuation that I haven't come across though. How many marks was this question? The marks provide a key as to how much explanation is required, I would think that trp operon repression based answers would require less volume of explanation (and so would be worth less marks) than answers on attenuation, given that attenuation is a slightly more complicated mechanism to explain. I could be mistaken on this.

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