HKS
nahhh im sure I lost more marks its just that im 100% sure I lost that 5 marks
VCE Biology Questions Thread
HKS hey if it makes you feel better, because you made me feel better knowing i wasnt alone because all my friends finished, but i also ran out of time and missed pretty much the same amount of questions. in my normal practice exams i had lots of time left, but for the actual exam i ran out of time. but it's ok hopefully, other people may be in the same boat and some people have said this was a harder exam, so if people finished, they may not have got it all right anyway 
7 months later
hello!!
I have no clue if this thread is still alive but I had a question about photosynthesis.
What does "photorespiration competes with photosynthesis" mean?
If photorespiration occurs, doesn't that mean photosynthesis can't occur?
thank you!
lune777 this is probably referring more to the fact that Rubisco's affinity to bind with O2 and CO2 changes depending on the conditions, and in a sense, these two substates compete to bind to Rubisco's active site. Therefore, the two processes compete with each other. Plus, you're not just going to have one Rubisco enzyme doing all the work in the plant, but rather heaps, so at points, some may bind to O2 and some may bind to CO2. I guess some cells would be undergoing photosynthesis, whilst some may undergo photorespiration depending on the situation. It's all about relative affinity and the levels of substate present. Overall, there will be a swing towards one or the other, and in those hot/dry conditions, there are C4 and CAM plants to accommodate for its negative impacts on Rubisco (i.e. increased photorespiration). I hope that makes sense!
7 days later
_sophiestudies_ thank you so much!! that makes lots more sense
lune777 no problem! I'm glad it makes more sense. Year 12 photosynthesis and photorespiration stuff can get confusing.
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.
a month later
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?
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.
woah
i never knew vce biology would teach you a new language...
_sophiestudies_ ahhh thank u so so much this was super helpful!!! i really appreciate your help ((:
9 days later
Tas real
2 months later
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
- Edited
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?
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.
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
Hope that helped
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