VCE Biology Question Thread

[nicks67]

Hi Everyone,

Just wondering does anyone have an appropriate definition for cell elongation?

Cheers.

[cosine]

What's the difference between positive and negative feedback loops?

[TheAspiringDoc]

What's the difference between positive and negative feedback loops?

So living organisms need to maintain homeostasis (the mechanism by a system maintains equilibrium). This is achieved by several means, including positive and negative feedback loops. Almost all homeostasis loops are an example of negative feedback. What happens is when presented with a stimulus, this system will oppose it and try and return to its original state. For example; when we get too hot, our body is like 'nah, I wanna cool down' and is against, or negative towards the stimulus. Positive feedback is the opposite; when presented with a stimulus, our systems will try to urge to continue, for example blood clotting - when a blood vessel is perforated, a clot will form. This clot is essential for maintaining homeostasis as it will keep our blood inside our body. The clot will then build up. Another example is our libido/sexual desires.

[cosine]

So living organisms need to maintain homeostasis (the mechanism by a system maintains equilibrium). This is achieved by several means, including positive and negative feedback loops. Almost all homeostasis loops are an example of negative feedback. What happens is when presented with a stimulus, this system will oppose it and try and return to its original state. For example; when we get too hot, our body is like 'nah, I wanna cool down' and is against, or negative towards the stimulus. Positive feedback is the opposite; when presented with a stimulus, our systems will try to urge to continue, for example blood clotting - when a blood vessel is perforated, a clot will form. This clot is essential for maintaining homeostasis as it will keep our blood inside our body. The clot will then build up. Another example is our libido/sexual desires.

Thanks for that mate!

What's the difference between Central Nervous System and Peripheral Nervous System?

[StupidProdigy]

The PNS is all the neurons outside of the CNS. CNS is comprised of the brain and spinal cord. PNS is comprised of sensory neurons (and motor neurons) which are sent to the CNS to be integrated with other info and processed and then a response is coordinated which in effect goes the reverse way (CNS sends a message through the PNS instead of receiving it). The response is made by using the motor neurons. PNS also contains the autonomic nervous system (the other stuff i was talking about was the somatic n.s branch) which regulates involuntary muscles in order to help the individual in a 'fight-or-flight' scenario. hope that kind of helps

[TheAspiringDoc]

Hi Everyone,

Just wondering does anyone have an appropriate definition for cell elongation?

Cheers.

Cell elongation is the lengthening of a cell during movement (like wriggling of a snake - I think?) or during the growth of an organism while undergoing cell differentiation (the process by which a type of cell becomes another.
You might be able to figure out a more sophisticated way of saying it though

[TwinNerd]

hi i was wondering if someone could help explain what excitatory and inhibitory neurons are.

thanks in advance:)

[TheAspiringDoc]

hi i was wondering if someone could help explain what excitatory and inhibitory neurons are.

thanks in advance:)

Okay, so to start off, they are not neurons but they are neurotransmitters. Neurotransmitters are the chemical substances released by the axon (firing end) of a neuron. Exitatory neurotransmitters are what stimulate/send messages to/across the brain. I guess they are called exitatory because they deliver information to the brain. Inhibatory neurotransmitters on the other hand are those that calm the brain and create balance (often when the exitatory neurotransmitters are being overactive). Examples of exitatory neurotransmitters include dopamine and epinephrine. Examples of Inhibatory neurotransmitters include serotonin and again, dopamine (I don't quite get how that's in both categories though, is it like when your parents read you a bed time story about string theory - but relaxing and informative?)

[TwinNerd]

cool thanks so much!

[mahler004]

Okay, so to start off, they are not neurons but they are neurotransmitters. Neurotransmitters are the chemical substances released by the axon (firing end) of a neuron. Exitatory neurotransmitters are what stimulate/send messages to/across the brain. I guess they are called exitatory because they deliver information to the brain. Inhibatory neurotransmitters on the other hand are those that calm the brain and create balance (often when the exitatory neurotransmitters are being overactive). Examples of exitatory neurotransmitters include dopamine and epinephrine. Examples of Inhibatory neurotransmitters include serotonin and again, dopamine (I don't quite get how that's in both categories though, is it like when your parents read you a bed time story about string theory - but relaxing and informative?)

It's because dopamine (and other neurotransmitters that can be inhibitor and excitatory) can act on multiple receptors - some are inhibitory, some are excitatory.

[TheAspiringDoc]

It's because dopamine (and other neurotransmitters that can be inhibitor and excitatory) can act on multiple receptors - some are inhibitory, some are excitatory.

Okay, so kinda like saying there are people who attend (bind to) TSFX lectures and there are people who attend AN lectures, and then there's this kid who attends both?
The only thing I don't get is that they are so contradictory, like one is all 'hectic' and information overload and the like, while the other is all like 'chill brah'.

[wobblywobbly]

Does anyone know if the different types of antibodies are being tested? ie IgE, IgA IgM ...

This question from the previous page was missed.

No. Not examinable.

[mahler004]

Okay, so kinda like saying there are people who attend (bind to) TSFX lectures and there are people who attend AN lectures, and then there's this kid who attends both?
The only thing I don't get is that they are so contradictory, like one is all 'hectic' and information overload and the like, while the other is all like 'chill brah'.

Kind of, although it's a bit of an odd metaphor It's probably better to think about the receptors here.

Caveat: Not a neuroscientist. I do know a little about signalling though.

To generate an action potential, you need an influx of sodium into the cell. Neurotransmitters act on receptors to cause this. Acting on the receptor generates a 'second messenger' (in this case, cyclic AMP, cAMP), which then causes the opening of the sodium channels (to cause the influx of sodium.) So there's two receptors that dopamine can act on, the D1 receptor (which causes an increase in cAMP) and the D2 receptor (which inhibits an increase in cAMP.) If dopamine acts on the D1 receptor, it's acting as an excitatory neurotransmitter, if it's acting on the D2 receptor it's acting as an inhibitory neurotransmitter.

(It's worth mentioning in passing that not all neurotransmitters act like this to cause an increase in sodium - some can act directly on sodium channels e.g. acetylcholine).

I don't think signal transduction is covered in this detail (if at all) in VCE any more.

(Again, not a neuroscientist)

[vox nihili]

Kind of, although it's a bit of an odd metaphor It's probably better to think about the receptors here.

Caveat: Not a neuroscientist. I do know a little about signalling though.

To generate an action potential, you need an influx of sodium into the cell. Neurotransmitters act on receptors to cause this. Acting on the receptor generates a 'second messenger' (in this case, cyclic AMP, cAMP), which then causes the opening of the sodium channels (to cause the influx of sodium.) So there's two receptors that dopamine can act on, the D1 receptor (which causes an increase in cAMP) and the D2 receptor (which inhibits an increase in cAMP.) If dopamine acts on the D1 receptor, it's acting as an excitatory neurotransmitter, if it's acting on the D2 receptor it's acting as an inhibitory neurotransmitter.

(It's worth mentioning in passing that not all neurotransmitters act like this to cause an increase in sodium - some can act directly on sodium channels e.g. acetylcholine).

I don't think signal transduction is covered in this detail (if at all) in VCE any more.

(Again, not a neuroscientist)

Just jumping in to emphasise this point. The vast majority of neurotransmitters don't work by a secondary messenger system because they're too slow.

As mahler004 suggested, you definitely don't need to know signal transduction to this level of detail, but it's actually a fantastic example to illustrate two things:

1. that ligands can act on different receptors and cause different effects
2. that there are different ways by which ligand-receptor interactions can give rise to a response

[grannysmith]

Just jumping in to emphasise this point. The vast majority of neurotransmitters don't work by a secondary messenger system because they're too slow.

As mahler004 suggested, you definitely don't need to know signal transduction to this level of detail, but it's actually a fantastic example to illustrate two things:

1. that ligands can act on different receptors and cause different effects
2. that there are different ways by which ligand-receptor interactions can give rise to a response

The first point has definitely been examined in the past - quite significant indeed!