Biology Unit 3 Questions Megathread

[jane1234]

Yep, you're right in saying that about CO2 playing a role in the light-independent stage but the "dark stage" is a bit misleading - it doesn't have to occur at night, it's just that those reactions are not reliant on light as an energy input. So both light dependent and independent reactions would be occurring at much higher rates during daylights and therefore more carbon dioxide would be consumed.

Ah okay, thanks

[WhoTookMyUsername]

do T cells proliferate as soon as they come into contact with an APC or do they find a B cell first (is this costimulation?)

They don't proliferate "as soon as" they meet their Ag but they don't need to find a B cell first. Costimulation is just signals provided by an APC to trigger proliferation.

how do cytotoxic T cells proliferate if they don't come into contact with antigen?

What makes you think they don't...? How else would they be activated?

Is the diagram inaccurate? Compound R almost appears to be an enzyme catalysising the reaction of Q into S, but the answers suggest Compound R can be turned INTO S as in an alternative metabolc pathway, is the diagram incorrect, or is this always how metabolic pathways are drawn?

Diagram is accurate. Compound R is not an enzyme, it's a compound. It can be converted to S, just like Q can (but presumably a different mechanism).

Enzymes are written next to arrows, they don't get their own box.

ahk, thanks a lot russ

so to activate t h, tc and b cells - an antigen has to come into contact with all 3 to stimulateall 3?

+ sorry if this question has been answered already ( i couldn't find it last few pages) but can Th cells activate B / T cells without being attached to antigen? (like find antigen, proliferate, then seperate from pathogen and find B cell?)

[Russ]

so to activate t h, tc and b cells - an antigen has to come into contact with all 3 to stimulateall 3?

B cells must come into contact with the antigen.
T cells must come into contact with a degraded peptide of the antigen
(there is a really poorly used naming convention)

A B cell must encounter the correct confirmation and then receive T cell help to activate
A T cell (whether Tc or Th) must encounter the presented peptide on an APC to activate (it receives help from the APC, Tc cells also get Th help)

+ sorry if this question has been answered already ( i couldn't find it last few pages) but can Th cells activate B / T cells without being attached to antigen? (like find antigen, proliferate, then seperate from pathogen and find B cell?)

As above, Th cells activate by presentation of peptides by an APC - they don't see the pathogen directly. Once activated they do not need to remain attached to the APC.

[WhoTookMyUsername]

Thanks so much Russ for answering my constant (6 pages or so) of immunity questions

I don't know what i would have done without you

This line of immunity questions will (possibly) cease for a short period of time (if your lucky until the weekend )


EDIT: - Do T cells differentiate (into Tc, Th etc. ) in the thymus or in the lymph?
(same with B cells, do they become memory in bone or lymmph?)

[humanimal]

2 Questions:

What is the difference between an action potential and a nerve impulse?
Heinemann says they are the same; The Penguin Dictionary of Biology (1980 edition, lol) says they are different, yet I'm finding it hard to wrap my head around the way it is described there; and practice exam companies seem to be as confused as me.

Do facilitated diffusion and active transport occur solely through 'protein channels', and if not, do they occur also through 'protein pumps' and 'carrier proteins'?
Heinemann defines the two processes as occuring through 'protein channels' and makes no mention of the other two membrane proteins.

Thanks in advance!

[scocliffe09]

2 Questions:

What is the difference between an action potential and a nerve impulse?

As far as I'm aware, the nerve impulse is the movement of the action potential along the axon.

Heinemann says they are the same; The Penguin Dictionary of Biology (1980 edition, lol) says they are different, yet I'm finding it hard to wrap my head around the way it is described there; and practice exam companies seem to be as confused as me.

Do facilitated diffusion and active transport occur solely through 'protein channels', and if not, do they occur also through 'protein pumps' and 'carrier proteins'?
Heinemann defines the two processes as occuring through 'protein channels' and makes no mention of the other two membrane proteins.

Protein pumps is a deceptive term which to me seems to imply that they require energy, which would rule them out of facilitated diffusion. I wouldn't use this term on an exam.
Facilitated diffusion can, however, occur through protein channels and carrier proteins, the fundamental difference being that carrier proteins change shape when the ion/substrate enters them.

see: http://bcs.whfreeman.com/thelifewire8e/pages/bcs-main.asp?v=&s=05000&n=00010&i=05010.01&o=|00510|00520|00530|00540|00550|00560|00570|00010|00020|00030|00040|00050|00060|00070|00080|00090|00100|00110|00120|00130|00140|00150|00160|00170|01000|02000|03000|04000|05000|06000|07000|08000|09000|10000|11000|12000|13000|14000|15000|16000|17000|18000|19000|20000|21000|22000|23000|24000|25000|26000|27000|28000|29000|30000|31000|32000|33000|34000|35000|36000|37000|38000|39000|40000|41000|42000|43000|44000|45000|46000|47000|48000|49000|50000|51000|52000|53000|54000|55000|56000|57000|99000| and
http://bcs.whfreeman.com/thelifewire8e/pages/bcs-main.asp?v=&s=05000&n=00010&i=05010.01&o=|00510|00520|00530|00540|00550|00560|00570|00010|00020|00030|00040|00050|00060|00070|00080|00090|00100|00110|00120|00130|00140|00150|00160|00170|01000|02000|03000|04000|05000|06000|07000|08000|09000|10000|11000|12000|13000|14000|15000|16000|17000|18000|19000|20000|21000|22000|23000|24000|25000|26000|27000|28000|29000|30000|31000|32000|33000|34000|35000|36000|37000|38000|39000|40000|41000|42000|43000|44000|45000|46000|47000|48000|49000|50000|51000|52000|53000|54000|55000|56000|57000|99000| for diagrams


Thanks in advance!

[scocliffe09]

Thanks so much Russ for answering my constant (6 pages or so) of immunity questions

I don't know what i would have done without you

This line of immunity questions will (possibly) cease for a short period of time (if your lucky until the weekend )


EDIT: - Do T cells differentiate (into Tc, Th etc. ) in the thymus or in the lymph?
(same with B cells, do they become memory in bone or lymmph?)

My impression is that T and B cells both differentiate upon activation, usually following contact with an antigen. This is most likely to occur in the lymph nodes.

[WhoTookMyUsername]

1) would 1 non - specific T cell coming into contact with antigen be able to give rise to a Tc and Th cell?

2) do we need to redifine (e.g. Red Blood cell (RBC)) for every part of question (e.g. 1 a , 2a?)

3) Does cellular respiration refer to any respiration in a cell, or the overall aerobic respiration chain, also can cellular respiration refer to anaerobic respiration?

4)Do yeast prefer to use oxygen / aerobic respiration
can they use ethanol to produce energy?

5) is it more accurate to call polymer of aminno acids poolypeptide or protein (VCAA says protein i think)

[Russ]

T cells do NOT differentiate to Tc/Th cells on contact with an antigen. That's already predetermined. When Th cells contact an antigen they will differentiate to form a specific subset of Th cell, each with a specific cytokine/receptor/protein/transcription factor etc. profile. So you have Th1, Th2, Th17 etc. cells, each fulfilling a different role.

In my exams I wouldn't need to define RBC at all, it's a recognised abbreviation. In VCE I'd say write "Red Blood Cell (RBC)" in the first part then use RBC from then on. Or just use erythrocyte if you want to sound fancy.

Depends what the person using it means, it just refers to the production of ATP. Most of the time it's used to mean aerobic though.

Yeast can use oxygen, ethanol is a byproduct and i'm reasonably sure it would be toxic to some extent

[HERculina]

which book explains immunity the best? especially 3rd line of defence

[WhoTookMyUsername]

I've only glanced through Nelson and Heinemann, but NOB does a pretty good job of it


Thanks Russ,
one of the teachers today said (dodgy q on STAV) that ethanol can be metablolised further to release more energy i guess this must be wrong? (there was no indication that oxygen was 'introduced' at a certain point in time -  if oxygen is present, do yeast prefer to repire aerobically

EDIT: Are Th cells need to stimulate Tc? (i'm still a bit confused )
EDIT 2: Is the output of the calvin cycle PGAL or Glucose more accurately?
VCAA seems to say glucose

also NOB says the first step to convert 5 C -> 2 3C with the addition of Co2 AND h20 but i cant find water as an input on any diagrams?

[HERculina]

isnt the H20 split in light dependent reactions already. the Hydrogen ions from water are carried to the calvin cycle in the form of ATP and NADPH. and the Os were released as oxygen gas in light dependent reaction.

i think PGAL is more accurately but on exam i would only say that along with the fact that it would be converted into glucose later on or other sugars.

Bazza16, do u have a copy of the STAV papers (i only have the 04 and 06 ones)
EDIT: dw, i found some more on VN

[amun]

yeah does anyone have ths stav paper for 2011

[jeppikah]

For the 2007 VCAA exam for Question 5a), it asks for you to name one well-recognised allergen. In the examiner's report, it states that fur and dust are incorrect answers. So why can't fur and dust be allergens? 

[pi]

EDIT: dw, i found some more on VN