VCE Biology Questions Thread

lune777

_sophiestudies_ thank you so much!! that makes lots more sense

_sophiestudies_

lune777 no problem! I'm glad it makes more sense. Year 12 photosynthesis and photorespiration stuff can get confusing.

lune777

I saw a diagram and was wondering how a build-up of pyruvate would slow down glycolysis?
Context: In cellular respiration, if there is an absence of O2 which causes a build-up of NADH (since it can't be converted back to NAD+ in ETC), this would slow down the Krebs cycle, thus there would be a build-up of pyruvate. This build-up causes glycolysis to slow down.

sarah99

Hi! I had a few questions - I would greatly appreciate any help 🙂

If interferon is released and gene expression is paused, isn't this bad for the cell and the organism, as it is unable to produce its own proteins to survive?
Does the MHC I represent the proteome of the cell?
NK cells kill cells with an abnormal or absent MHC I right - Why might some cells have an absent MHC I marker?

_sophiestudies_

sarah99 let me see if I can help!

Interferons have antiviral properties, so they're going to try and stop virus replication. In order for viruses to replicate, they're going to take over a host cell and its gene expression machinery, meaning interferons will pause gene expression to prevent viral proteins from being produced (aka preventing viral replication). I'm assuming it would just be preventing gene expression of viral genes, not the cell's genes. That said, the cell would probably have to be cleared from the body anyway because it's already virally infected. The interferons will just prevent the virus from spreading further.
No. The proteome includes all the proteins expressed in an organism. This includes MHC I, but also other proteins in the organism too.
Viruses and tumours/cancerous cells can downregulate the expression of MHC I markers, meaning they can be absent. Some may be present, presenting viral or tumour/cancer peptides (i.e. antigens). Some would function abnormally as well. NK cells will just look to see if normal MHC I markers are being expressed or stressed/abnormal markers, and if there's been any downregulation in the number of MHC I markers.

sarah99

_sophiestudies_ ahhh thank u so so much this was super helpful!!! i really appreciate your help ((:

Tas

woah
i never knew vce biology would teach you a new language...

NOSSALSUCCESSBUTNOTGOING

Tas real

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

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