Can someone please explain how the body distinguishes between self and non self?
This has been explained a few times here already, so don't be afraid to scroll a bit

Self molecules are those molecules not recognised by immune cells. Non-self molecules are those molecules recognised by immune cells. This really is the fundamental difference between the two. Immune cells express receptors to non-self molecules and don't express receptors to self. That's how it tells the difference*
*obviously there's a lot more complexity here, but it would be well and truly outside of the course
Also, does the post translation modification of insulin occur in the RER or golgi. This was a MC choice question on my exam. The modification was glycosylation.
Thanks
Golgi. I think that's probably a bit outside the course, although you should know in VCE that most post-transcriptional modifications do happen in the Golgi. This isn't actually true, but that's how it's presented in VCE unfortunately.
MHC Class I markers are on every nucleated cell in the body. These are NOT responsible for presenting antigens. These MHC Class I markers are 'tagged' or 'labelled', meaning that they have these specific MHC markers so that all the other cells of the body can recognise them as self, and so they do not get destroyed.
MHC Class II markers are found on B Lymphocytes, T lymphocytes, Macrophages and Dendritic cells. These cells actually have both MHC Class I and MHC Class II. These Cells engulf foreign pathogens, digest them with their lysosomes, and present antigenic fragments on the Class II markers.
Just going to pop in here. This description of MHC class I markers is completely wrong, sorry. They do actually present antigens. I'm not sure you need this knowledge for your VCE exams, but MHC class I molecules present antigens from within the cell. So if you've got a viral infection, viral antigens are presented on MHC class I molecules. They're on all nucleated cells because all nucleated cells can be infected by viruses. CD8+ T-cells see the antigen expressed on the MHC class I and blast the shit out of the cell as a consequence.
Also really important to note that
MHC molecules only present to T-cells. B-cells bind free antigen.
No one answered me
What happens when an action potential passes along an axon in terms of the ions coming in and out? I know that Sodium ions rush in, and Potassium ions rush out. Because the sodium ions are going from the outside the neuron and into it, from a high concentration to a low one, would this be considered facilitated diffusion? My teacher says it's active transports, because energy is required, but how can energy be required if the ions are going from high to low concentration?
Thanks guys
Active transport plays no role in the propagation of an action potential along the axon. What jyodesh.com said is completely correct, though out of the course. Pumps set up concentration gradients in neurones, but it is actually diffusion that leads to the propagation of an action potential along the axon.
How do phagocytes such as macrophages know exactly where/what a foreign pathogen is? Is it because the MHC markers of the phagocyte detect the foreign antigens on the pathogen, and hence engulf it? Also, if this is true (not sure, so what im gonna say might also be wrong), is phagocytosis non-specific, although it responds to antigens, because every response is the same to any type of antigen? Like whether it's a bacterium, or a virus, it would still engulf it the same way, so it's non-specific. But specific immunity is when SPECIFIC antibodies are made for an antigen?
My main question is if you cannot be bothered reading that above
: do phagocytes interact with antigens, and upon not recognising them, engulf the pathogen?
Thank you
Phagocytes have receptors for a lot of different things that tell them that they're dealing with a pathogen. Cells of the innate immune system are non-specific, but they are still able to recognise molecules associated with lots of pathogens and therefore they can generally tell whether something is or isn't an invader.
Furthermore, phagocytosis is also mediated by antibodies. Phagocytes express receptors that allow them to sense cells that have been bound by antibodies. The antibodies actually help to identify these cells and also aid the process of phagocytosis.