Biology Unit 3 Questions Megathread

[Charmz]

Pretty sure both are correct.

And can anyone explain buffers. I got the answer somewhere but I can't remember. A lot of practice papers mention them.

[epinephrine]

Simple, they are substances that combine with or release hydrogen ions in a solution as required to
prevent a change in the pH of the solution.

Theres different kinds, e.g. protein buffers such as haemoglobin which can act as a buffer, and some
are intracellular buffers such as phosphate buffers. Oh and there are also bicarbonate buffers (act in blood).

Thats just off the top of my head but in saying that I don't think we would be required to know to really
in depth. Perhaps its good to just have a grasp of how they work. 

[pi]

And can anyone explain buffers. I got the answer somewhere but I can't remember. A lot of practice papers mention them.

You mean amino acids acting as buffers?

If so: an alpha amino acid (the normal ones that make proteins, alpha for the central carbon) have three main groups, the amine (-NH₂), the carboxylic acid (-COOH) and the Z group attached to the alpha carbon. If we take glycine (the simplest amino acid -I think), the Z group is a H. In a pH of 7, glycine, instead of having the amine and carboxilic groups as they are, from a zwitterion (don't need to know that word for bio). Basically, a zwitterion has a neutral overall charge but has charged areas. IN the case of amino acid at ph 7, it donates and accepts a proton and forms N⁺H₃ and COO^-. In a basic solution (pH>7), it will only donate a proton (only the COO^-). In an acidic environment (pH<7), it will accept a proton (only N⁺H₃). Hence, an amino acid (only by itself, not when in a polypeptide/protein) can accept and donate protons depending on the surrounding pH, effectively neutralising the solution, therefore acting as a pH buffer.

Thats just my chem 3+4 knowledge plus my ex-bio 3+4 knowledge chucked in a para Hope that makes sense

[Charmz]

And can anyone explain buffers. I got the answer somewhere but I can't remember. A lot of practice papers mention them.

You mean amino acids acting as buffers?

If so: an alpha amino acid (the normal ones that make proteins, alpha for the central carbon) have three main groups, the amine (-NH₂), the carboxylic acid (-COOH) and the Z group attached to the alpha carbon. If we take glycine (the simplest amino acid -I think), the Z group is a H. In a pH of 7, glycine, instead of having the amine and carboxilic groups as they are, from a zwitterion (don't need to know that word for bio). Basically, a zwitterion has a neutral overall charge but has charged areas. IN the case of amino acid at ph 7, it donates and accepts a proton and forms N⁺H₃ and COO^-. In a basic solution (pH>7), it will only donate a proton (only the COO^-). In an acidic environment (pH<7), it will accept a proton (only N⁺H₃). Hence, an amino acid (only by itself, not when in a polypeptide/protein) can accept and donate protons depending on the surrounding pH, effectively neutralising the solution, therefore acting as a pH buffer.

Thats just my chem 3+4 knowledge plus my ex-bio 3+4 knowledge chucked in a para Hope that makes sense

Is there a more simple way of putting it. :S

[pi]

Is there a more simple way of putting it. :S

Basically, an amino acid is a pH buffer in that it can donate or accept a proton depending on the environment it is in. If in acidic env, it will accept. If in basic env, it will donate.

I think that amount of knowledge will suffice.

[epinephrine]

Hey do you guys reckon we should know all of the homeostatic mechanisms?
such as the action of ADH, thyroxine etc?

Or is it best to just know the general principles behind feedback mechanisms,
since when I checked in the VCAA exams they gave information in their
questions for most, well obviously except for stuff about glucose regulation,
yet the trial exam companies ask about the intricate details pertaining to the
regulation of each and every variable 

[jane1234]

If a neurotransmitter is NOT broken down (i.e. the enzyme that breaks it down is denatured) will this result in continual stimulation of the postsynaptic nerve, or no impulse as the neurotransmitter can't be broken down and reused? On most exams it's the former, but TSSM just said it's the latter...  :idiot2:

[epinephrine]

I think its the former, I don't really like TSSM exams since they usually have something
wrong in their exams. 

[Charmz]

Just watch the video and all your doubts will be cleared up. As for chemokines, you don't need to know it. It's just extra information if you are interested.

[scocliffe09]

If a neurotransmitter is NOT broken down (i.e. the enzyme that breaks it down is denatured) will this result in continual stimulation of the postsynaptic nerve, or no impulse as the neurotransmitter can't be broken down and reused? On most exams it's the former, but TSSM just said it's the latter...  :idiot2:

See VCAA 2009 Q6 (this is the most important stuff you need to know re neurotransmitters)
overstimulation is the main problem. If for some reason, neurotransmitter synthesis were being impeded, then i suppose breakdown would cause issues with regard to not having enough - but this is less likely methinks.

[epinephrine]

Hey do you guys reckon we should know all of the homeostatic mechanisms?
such as the action of ADH, thyroxine etc?

Or is it best to just know the general principles behind feedback mechanisms,
since when I checked in the VCAA exams they gave information in their
questions for most, well obviously except for stuff about glucose regulation,
yet the trial exam companies ask about the intricate details pertaining to the
regulation of each and every variable 

[epinephrine]

Is it just me or does it seem like VCAA loves students to give comparative statements?

They've made a remark about this in most of the past exams that I've taken a look at. Well
I guess at times it appeared as though the question was not asking for a comparison whereas the
answer supplied suggested otherwise    So what do you guys reckon would it be safe to give a
comparison for some questions just in case and how are you guys able to decipher if the question
is asking us to make a comparative statement?

[lexitu]

Hey do you guys reckon we should know all of the homeostatic mechanisms?
such as the action of ADH, thyroxine etc?

Or is it best to just know the general principles behind feedback mechanisms,
since when I checked in the VCAA exams they gave information in their
questions for most, well obviously except for stuff about glucose regulation,
yet the trial exam companies ask about the intricate details pertaining to the
regulation of each and every variable 

No way, exactly as you said. It's only other companies that mislead you into thinking that you need to know everything. You will be given enough information. You will need to know at least one example though if you are given an open-ended question and are required to show a pathway.

Sometimes VCAA exams are a bit ambiguous but overall they're very diligent and excellent at testing concepts in a holistic way. Yeah, they love comparisons I f you are genuinely unsure, go for it. There's nothing wrong with giving more information as long as you are addressing the question and not adding incorrect information. Obviously it would be inefficient to do so, though.

[person]

How much chemistry do we have to know for the exam?

[lexitu]

Pure basics, don't let companies fool you in thinking you need to know complex molecular structures or anything like that