Biology Unit 3 Questions Megathread

[vexx]

The control is whichever experiment where the variable you're altering (tonicity) will not affect the variable you're measuring. A pure water solution or a pure sugar pill (for drug testing) is not always an appropriate placebo because it may have an effect

so the egg placed in the isotonic solution has no effect on the variable (ie. increase or decrease in weight) and thus can be deemed a control?

basically - in that experiment, if you were to ask to name the control that would be it.

[jbebbo]

As trophic refers to the Carbon Source, why are prions and viruses 'non - trophic' if they get carbon from other organisms?

 Are CAM plants C4 or C3, Neap says C4, teacher said C3

Heterotroph and autotroph are applied to organisms, but prions and viruses technically aren't organisms - thus the 'non-trophic'.

I would agree with Hercules; CAM is another category, just like C3 and C4. But seriously, the VCAA never ask about CAM, and only ever occasionally about C3 and C4

[WhoTookMyUsername]

Thankyou,

A question i asked a while ago: Why does Pyruvate need to be converted into Lactic acid in humans when they are both toxic?

A response i recieve (that i thought was correct until today) was that it needed to recycle NAD, but because the body is simply rearranging the structure, and more NAD can be created, my teacher said that its due to 'concentration gradients' of pyruvate that are needed to ensure proper function of aerobic respiration when it resumes. Can anyone confirm or shed light upon this?
Thanks

[HERculina]

^ Oh good question. im also wondering why too now   
yea why cant just the glycolysis part of anaerobic fermentation occur, cause thats the actual stage that produces the 2ATP :|

[shinny]

I still stick by the need to recycle NADH. Wiki seems to agree with me. I have no idea about this pyruvate gradient thing your teacher is referring to. To me, the more pressing issue is the NAD+/NADH ratio which is required to be kept low in cells to drive redox reactions forward. Furthermore, simply 'creating more NAD' itself requires energy. Where's this energy coming from then?

[scocliffe09]

I still stick by the need to recycle NADH. Wiki seems to agree with me. I have no idea about this pyruvate gradient thing your teacher is referring to. To me, the more pressing issue is the NAD+/NADH ratio which is required to be kept low in cells to drive redox reactions forward. Furthermore, simply 'creating more NAD' itself requires energy. Where's this energy coming from then?

Yep I agree with Shinny. More specifically the NAD+/NADH ratio is required to enable glycolysis to continue and thus to allow continued production of ATP (in the short term), hence conversion to lactic acid.

[HERculina]

I still stick by the need to recycle NADH.

is this referring to how the NADH from glycolysis dumps the H onto the last electron acceptor (pryuvate) to form lactic acid = regenerating NAD

[jbebbo]

I still stick by the need to recycle NADH.

is this referring to how the NADH from glycolysis dumps the H onto the last electron acceptor (pryuvate) to form lactic acid = regenerating NAD

Pretty much.
Also, you might want to be careful about NADH, NAD+ and H+ (technically H+ is just a proton) - the VCAA are really annoying and specific about always writing NAD+ and H+

[HERculina]

oh ok. whats the difference between NADPH+ and NADP + H.
i see this written in different ways - a bit confusing.

[dooodyo]

could someone explain why people with short and stocky statures have a greater chance of
survival compared to people with taller and skinnier body shapes if they both were suffering
from hypothermia?

[vexx]

could someone explain why people with short and stocky statures have a greater chance of
survival compared to people with taller and skinnier body shapes if they both were suffering
from hypothermia?

it has to do with the taller/skinnier person have a greater surface area to volume ratio than the short/stocky person, so loses more heat as more body surface is exposed.

[shinny]

could someone explain why people with short and stocky statures have a greater chance of
survival compared to people with taller and skinnier body shapes if they both were suffering
from hypothermia?

It's a bit vague, but going by unit 3/4 knowledge, I'd assume the answer is SA:V ratio. i.e. they have less surface area to lose heat out of. I've said it many times; write out a list of all the common principles and refer to it whenever you get stuck. Almost everything in the unit 3 exam invariably comes back to these few simple principles.

[dooodyo]

@ Shinny : apart from SA:V ratio what other common principles did you mean?

[shinny]

@ Shinny : apart from SA:V ratio what other common principles did you mean?

Can't quite remember all of them, but diffusion and SA:V both inevitably come up in some strange form or manner often without people realising, then there's others which are a bit less abstract such as the stimulus-response model, all those enzyme rules regarding temperature, pH etc. Just flick through each chapter and identify them.

[dooodyo]

1. No

and

2. I would say yes.