AQA BIOL2 ~ 21 May 2012 ~ AS Biology

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sruti1995

Comparing the base sequence of a gene provides more information than comparing
the amino acid sequence for which the gene codes. Explain why

Can someone tell me what they would put as a 4mark answer please? Thank you :smile:

Reply 1581

king101

Originally Posted by Dorkins
When water vapour diffuses out of the stoma, you will lose a mark for calling it osmosis; osmosis is across a semi permeable membrane

No, because it all travels from the bottom upwards. How would air get in?

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Thanks for that!. So say even if you put since the air spaces which have a greater humidity than the atmosphere and therefore a greater water potential than that of the atmosphere the water would diffuses out into the atmosphere? (and not moves the stuff about osmosis?)

Reply 1582

IAmMclovin

Original post by Spellstheend

I thought starch and glycogen are highly branched, cellulose is the only unbranched one of the three

Starch consists of:
Amylose which is unbranched

Amylopectin which is branched

But the textbook/specification refers to starch as unbranched

Glycogen is branched

Cellulose is not, as you rightly said :smile:

Reply 1583

Joshmeid

Has anyone actually been looking through the grade boundaries?

I've been through them and they don't seem to harsh.

June 2009 - 67/85 for 140 UMS (78%)
Jan 2010 - 64/85 for 140 UMS (75%)
June 2010 - 73/85 for 140 UMS (86%)
Jan 2011 - 64/85 for 140 UMS (75%)
June 2011 - 73/85 for 140 UMS (86%)
Jan 2012 - 72/85 for 140 UMS (85%)

Reply 1584

IAmMclovin

Original post by Lol_Fish

Co. Ten. theory, as you know a tension (pressure gradient) is created in the Xylem vessel, and thus when cut, because it has a lower pressure due to the tension generated, than atmospheric pressure, and pressure moves along a pressure gradient, and so the air is drawn into the xylem as it's pressure is lower to that of the atmosphere, that's why the air is "drawn" in.

Yes, thats what I was arguing? haha
I was saying that air is drawn in due to cohesion tension, and sap wouldnt leak out

Hi everyone! :hi:

Ive been stalking this thread, but couldn't be bothered to sign in lol
I'm dreading this paper, i too have a strong feeling its going to be a mean one :mad:

Also i feel like it just goes on and on.
And to top it all off its in the afternoon! I bet i'll fall asleep half way through :eek:

Reply 1587

IAmMclovin

Original post by Mocking_bird

Well we were given a question,
"describe one piece of evidence that supports the root pressure theory and explain how"

Evidence: Freshly cut root still exudes sap
Explanation: Root pressure involves a positive hydrostatic pressure which is responsible for pushing water up the stem of a plant. This is generated by endodermal cells actively pumping ions into the xylem... etc etc you get the point.

If i'm right in saying - no, not both are present, as they are both just theories but cohesion-tension is the most widely accepted theory.

Ok, probably safest to put "cyanide is a respiratory inhibitor ---->stops root pressure by preventing active transport of salts", or something along the lines of less O2/glucose available=less root pressure, so we both get the marks :tongue:

Reply 1588

king101

if you put since the air spaces which have a greater humidity than the atmosphere and therefore a greater water potential than that of the atmosphere the water would diffuses out into the atmosphere? (and not moves the stuff about osmosis?)

So does water diffuse out from the air spaces/stomata or is it by osmosis? Because for naily all the factors affecting transpiration it always says theres a higher water potential inside leaf or near stomata compared to atmosphere therfore water potential grad is greater.......So DOES THIS MEAN WATER DIFFUSES OUT? OR WATER MOVES BY OSMOSIS OUT??

Reply 1589

TipTapToe

Original post by sruti1995

- Dna is triplet so 3 bases code for one amino acid; so you'll have 3x the amount of info.
- Dna is degenerate, so more than one base sequence can code for a specific amino acid. So the same amino aside sequence can be coded for by complete different sequence of bases.
- Dna contains introns; these are removed before the 'conversion' to amino acids.
- Some different organisms may not have the same protein (you cannot compare amino acids sequence of two different proteins). However, DNA is universal so even if you can't find a similar protein you can compare bases. <--I have no idea what to put for the 4th mark but

Different (base) triplets code for same amino acid = 2 marks

(edited 11 years ago)

Reply 1590

HopefulFutureMedic

Oohh and can someone kindly help me out with question 2b - June 2009 paperI know its simple, but i got the wrong answer!
Thankyou in advance :biggrin:

Reply 1591

Monster Mnch

I got a MS answer for counter-current, but has anyone got one for the other two adaptations for xerophytes and insects?

Reply 1592

Mocking_bird

Original post by IAmMclovin

The MS answer was:
Suitable accepted evidence, 1 mark for evidence and 1 mark for explanation
EITHER e.g.guttation
(only) upward pressure could force liquid water out of leaves;
OR
Sap exuding from a cut, rooted stem;
(only) upward force could make this happen;

Reply 1593

sruti1995

Original post by tiptaptoe

- dna is triplet so 3 bases code for one amino acid; so you'll have 3x the amount of info.
- dna is degenerate, so more than one base sequence can code for a specific amino acid. So the same amino aside sequence can be coded for by complete different sequence of bases.
- dna contains introns; these are removed before the 'conversion' to amino acids.
- some different organisms may not have the same protein (you cannot compare amino acids sequence of two different proteins). However, dna is universal so even if you can't find a similar protein you can compare bases.

thank you so much !

Reply 1594

Mocking_bird

Original post by HopefulFutureMedic

Oohh and can someone kindly help me out with question 2b - June 2009 paperI know its simple, but i got the wrong answer!
Thankyou in advance :biggrin:

Only look at one of the strands :smile:

3 bases code for 1 amino acid.
So separate up the strand by putting a line after every 3rd base.
You will see there are 4 amino acids

Reply 1595

sruti1995

Its 4, because if you count it in triplets, just on one of the rows, its 4 :smile:

Reply 1596

Monster Mnch

Original post by Saraah_x

It
Probably
Might
Always
be
True

Stages of mitosis :biggrin:

(even the the b doesn't stand for anything..)
Interphase
Prohphae
Metaphase
Anaphase
Telophase

You can also something my teacher told me: Please Make Another Two - and you should remember interphase pretty simply. :smile:

Reply 1597

username570224

Sup everyone! Hope rev for this is going well, just working through papers now :/

Can anyone give a definition for cell differentiation, tissue, organ and organ system? I know what they are, it;s just I have difficulty in putting it into words that suit the MS :frown:

Reply 1598

EffKayy

For any of you who have cassio calculators:

Do you know how to change fractions to decimals permanently, like is there a setting, without pressing the SD button..?

Reply 1599

idunnotbh

Original post by The Assassin

Yeah questions are a good idea.

1) Explain how the structure of starch is related to its function. (5)

2) Describe the molecular structure of DNA and how it's replicated. (6)

3) How would an air bubble in the xylem vessel stop transportation of water? (4)

this is long

1) starch is a storage molecule in plants.
It's made up of many polysaccharide chains of alpha glucose, mainly amylose and amylopectin.
Amylose consists of coiled up helical chains of alpha glucose, which make starch compact and therefore useful as a storage molecule.
Amylopectin is branched at either end of starch and therefore allows the glycosidic bonds to be easily hydrolysed and glucose to be broken free.
Starch is also insoluble and so there is no osmotic gain or loss of water

2) DNA is made up of two polynucleotides which run anti-parallel. Each nucleotide consists of a phosphate, a deoxyribose sugar and a nitrogenous base. Hydrogen bonds form between complimentry bases (A+T) and (C+G) and the sugar phosphate backbone makes DNA stable.
DNA replication is semi conservative.
DNA helicase breaks the hydrogen bonds between base pairs, and the two polynucleotides are seperated. Free nucleotides then come and form hydrogen bonds with their complimentry base pairings and DNA polymerase then joins the two polynucleotides together.

3) Water has cohesive properties due to hydrogen bonds, and it therefore forms a continuous chain travelling up the xylem and out of the stomate through transpiration. If an air bubble were to enter, the chain would be broken and there would be no upward flow and therefore no transpiration