VCE Biology Question Thread

[PhoenixxFire]

^You don't need to know about meiosis. You just need to understand aneuploidy and polyploidy in the context of how it can affect the genetic makeup of a population, not how it occurs.

[Chocolatepistachio]

why is the answer for this diffusion wouldn't the neurotransmitter be leaving via exocytosis

[Sine]

why is the answer for this diffusion wouldn't the neurotransmitter be leaving via exocytosis

Yeah, ACh leaves the presynaptic neuron via exocytosis.

Possibly the person who wrote the question got confused between ACh crossing the synapse which is done via diffusion.

[Harrycc3000]

Why do lipids contain a greater portion of carbon and hydrogen atoms relative to oxygen atoms

Hi chocolatepistachio,
Lipids contain a greater portion of carbon and hydrogen because it gives them non-polar properties, which characterise it as a lipid. If it were to have an oxygen atom, then the molecule would be more polar and therefore would make it water-soluble making it not a lipid.

If you don’t know what polarity is referring to, a molecule is polar when it has a delta(slightly) positive side and a delta negative side. This forms when a very electronegative atom is a part of a certain molecule. Due to its high electronegativity, this atom attracts or ‘pulls’ electrons towards itself from the adjacent atoms (like hydrogen which would have lower electronegativity) its bonded to. This forms a delta negative side(on the atom in which the electrons are ‘pulled’ towards’ and a delta positive side (on the atom in which the electrons are ‘pulled’ away). A polar molecule is water soluble because it water can bond via its delta negative electron atom binding to a delta positive atom on the polar molecule and its delta positive hydrogen atom binding to a delta negative atom on the same molecule. Because oxygen has high electronegativity (due to its high core charge) an atom with a higher proportion of oxygen atoms is more likely to be polar and therefore more watersoluble and less fat soluble making it have less lipid-like properties.

[Corey King]

Hey guys,
Does anyone know the difference between a peptide and a polypeptide?
Looking at my textbook and googling leads me to thing they are the same thing, but they keep being differentiated as if they aren't.
Are they not both just a chain of two or more amino acids joined via peptide bonds?
Many thanks,
Corey

[I don\'t know]

Hey guys,
Does anyone know the difference between a peptide and a polypeptide?
Looking at my textbook and googling leads me to thing they are the same thing, but they keep being differentiated as if they aren't.
Are they not both just a chain of two or more amino acids joined via peptide bonds?
Many thanks,
Corey

Isn't a peptide, a chain that is composed of around 2-50 amino acids while polypeptides are amino acid chains composed of more than 50 amino acids??? I'm not sure if that is correct but that's what I learned. Idek.

[Chocolatepistachio]

Two neighbouring neurons are at rest. Neuron A has a resting membrane potential of -80mV, neuron B has a resting membrane potential of -70 mV. Which is likely to be true?
A neuron A has more k+ channels open than Neuron B
B Neuron B has more k+ channels open than Neuron A
C neuron A has more Na+ channels open than Neuron B
D Neuron B has more Na+ channels open than Neuron A

Would it be d more Na+ channels open making more Na+ flow into the cell making it more positive
Wouldn’t d and a both be right

[Erutepa]

Hey guys,
Does anyone know the difference between a peptide and a polypeptide?
Looking at my textbook and googling leads me to thing they are the same thing, but they keep being differentiated as if they aren't.
Are they not both just a chain of two or more amino acids joined via peptide bonds?
Many thanks,
Corey

From my quick research there doesn't really seem to be a universally accepted distinction between peptides and polypeptides. It seems the most popular convention is that a peptide refers chains of about 2 amino acids to about 50-100 where they begin being large enough to be referred to as a protein themselves whereas polypeptides seem to commonly be used as a subset of peptides - peptides of about 10 amino acids to about 50-100 in length. This site here does a good job as summarising this relationship. However, some sources do seem to exclusively refer to peptides as amino acids chains of 2-10ish in length, with larger chains being referred to as polypeptides until about 50-100 in length where it is then a protein.
That all being said, I these are just loose naming conventions and are not important for VCE biology. You just need to know that a polypeptide is a chain of amino acids as the study design mentions no distinction between peptides an polypeptides.

Two neighbouring neurons are at rest. Neuron A has a resting membrane potential of -80mV, neuron B has a resting membrane potential of -70 mV. Which is likely to be true?
A neuron A has more k+ channels open than Neuron B
B Neuron B has more k+ channels open than Neuron A
C neuron A has more Na+ channels open than Neuron B
D Neuron B has more Na+ channels open than Neuron A

Would it be d more Na+ channels open making more Na+ flow into the cell making it more positive
Wouldn’t d and a both be right

I can't unfortunately help with this question without first learning more about neurons and membrane potentials and the distinction between increases potassium ion concentration and sodium ion concentration on these potentials. But I can say that this is not in the current VCE study design so it is not crucial to know. By all means learn about it for fun, but just know that this stuff won't pop up on the exam.

[Calebark]

Two neighbouring neurons are at rest. Neuron A has a resting membrane potential of -80mV, neuron B has a resting membrane potential of -70 mV. Which is likely to be true?
A neuron A has more k+ channels open than Neuron B
B Neuron B has more k+ channels open than Neuron A
C neuron A has more Na+ channels open than Neuron B
D Neuron B has more Na+ channels open than Neuron A

Would it be d more Na+ channels open making more Na+ flow into the cell making it more positive
Wouldn’t d and a both be right

Spoiler tag for this one as it's off-topic lol

Erutepa is correct in that this isn’t relevant to VCE Biology. I know this stuff used to be more relevant to VCE (action potentials used to be a part of the study design!) but they were removed before my time.

I believe the answer would be Neuron A has more K+ channels open than Neuron B. Your line of thinking was close, but we have to take into account that the permeability of K+ is roughly 20 times more than the permeability of Na, so it’s a much stronger determinant when calculating RMP.

We can actually see how the permeability of K+ affects the resting membrane potential by calculating the resting membrane potential ourselves. If you’re curious, you can see it in this video by watching from the start up to 6:45, which goes through something called the Goldman-Hodgkin-Katz Equation — it'll do a much better job than what I could. Naturally if it’s a bit confusing, that’s okay, because like Erutepa said this is not relevant to the study design.

[Chocolatepistachio]

The extracellular face of the membrane is positively charged for a neuron at rest. Why don’t negative ions exit from the cell to balance charges on the outside surface of the membrane?
A the negative charge inside the cell is carried by large proteins that cannot diffuse through the membrane
B. All of the chloride ions are already outside the cell
C. The positive charges outside the cell repel negative ions
D. There are no negative ions inside the cell

Would it be a

[vox nihili]

The extracellular face of the membrane is positively charged for a neuron at rest. Why don’t negative ions exit from the cell to balance charges on the outside surface of the membrane?
A the negative charge inside the cell is carried by large proteins that cannot diffuse through the membrane
B. All of the chloride ions are already outside the cell
C. The positive charges outside the cell repel negative ions
D. There are no negative ions inside the cell

Would it be a

Yes

Not sure I entirely agree with the way that the answer has been phrased but it's the most correct of the options.

[jm08]

In the production of monoclonal antibodies outside of the body, why do the B lymphocytes from mice that are already producing antibodies need to be fused with myeloma cells? Why is this fusion necessary?

[PhoenixxFire]

^What do you think? What are you stuck on?

Note for everyone posting questions here, we exist because we want to help students but we won't just do your homework for you, that doesn't teach you anything.

[jm08]

I think my question was clear and I told you what I was stuck on. If you think that is doing my "homework" for me then so be it.

[PhoenixxFire]

I think my question was clear and I told you what I was stuck on. If you think that is doing my "homework" for me then so be it.

No one questioned the clarity of your question, rather whether you had attempted it before posting it here. And no you have given absolutely no indication of what about this question you are finding hard.