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AQA BIOL2 Biology Unit 2 Exam - 26th May 2011

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the jan 11 paper about Q how to calculate the cell cyle or sumfin like that, answer was 3, i was like wtf???

jan 11 was disgusting lol

any explanations?

Reply 641

ScienceGeek3

Original post by Kandy_Kain_94

Can someone explain these please:

Transpiration Pull

Root Pressure

cohesion-tension hypothesis

Thanks

Transpirational pull is when water lost from mesophyl cells by evaporation into air spaces is replaced by water moving in from a neighbouring cell via osmosis along a water potential gradient. Water moves up the stem in the xylem due to root pressure and cohesion tension. Transpiration pull also occurs in the cohesion tension theory.

Root pressure I believe is when the casparian strip in the endodermis prevents water moving alonng the apoplastic pathway and causes it to move along the symplastic pathway. Endodermal cells actively transport salts into the xylem. In order for water to then enter the xylem it must now be in the cytoplasm of the endodermal cells. The active transport of ions into the xylem lowers the water potential gradient and thus water moves into the xylem via osmosis along a water potential gradient. This creates a root pressure force, which helps to move water up a plant.

The cohesion tension theory can be broken down into steps:-
-water evaporates from the leaves of the plant due to transpiration
-water molecules form hydrogen bonds between one another, sticking to each other know as cohesion
-water forms a continuous, unbroken pathway across mesophyll cells and down the xylem
-the column of water is drawn up due to the transpiration at the leaves
-water molecules also stick to the inside of the xylem vessel know as adhesion
-the entire column of water is pulled up the xylem vessel due to the tension put on the xylem by transpirational pull.

(edited 12 years ago)

Reply 642

ScienceGeek3

Original post by mithunaa

Do we need to know about myoglobin?

Not that I know of, I believe it's only haemoglobin :smile:

Reply 643

lolo-x

Original post by Kandy_Kain_94

Can someone explain these please:

Transpiration Pull

Root Pressure

cohesion-tension hypothesis

Thanks

Cohesion Tension theory:
the cohesion part is the attraction between individual water molecules, caused by the hydrogen bonds between them. It causes 'surface tension' and the 'meniscus' on the surface of water and, in the xylem of plants, causes each water molecule in a xylem vessel to be attracted to its neighbours.
Thus, if a water molecule is lost from the TOP of a plant, it will pull on its neighbour, which will pull on its neighbour, which wil....etc etc, all the way to the BOTTOM of the plant, where water will be attracted into a root hair.

The TENSION part refers to the water being SUCKED up the plant, as aopposed to being PUSHED up the plant. The pressure inside each xylem vessel is thus negative (BUT positive inside the phloem, hence maple syrup and latex coming out when a tree is tapped), in just the same way as the pressure is negative inside a drinking straw when you suck.

This is the opposite of the situation inside domestic water pipes, where the pressure is poitive and water squirts out when you nail through a pipe!

So....water is lost from the leaves through evaoration,; it sucks water up the plant and the attraction between water molecules causes the water to be pulled all the way up the plant.

Reply 644

F1's Finest

Original post by parallal

I absolutely hate HSW questions. Give me just recall questions and I'd pass this exam with flying colours.
Good luck getting your A. :smile:

I'm just trying to scrape a B. That stupid ISA really messed up my AS grade.

yeah thanks :smile:

my isa i got a bang on B :angry:

thats why im trying to make it up tommorow. well, anyhow i miss my biology and chemistry overall grades by a couple of marks off an A, i am not gonna be a happy bunny at all !

good luck to you for tommorow !

Reply 645

SuperEagle

hey don't know if this will help but this is what my teacher thinks will come up:

Breathing rate in fish and insects
DNA structure
Mitosis
Transpiration
Cellulose
Tissue Fluid and capillaries
Antibiotic resistance
Diversity and man's influence
Classification

This is just his predictions but most of what he predicted for january came up so you never know :biggrin:

Reply 646

mithunaa

Original post by ScienceGeek3

Not that I know of, I believe it's only haemoglobin :smile:

thanks!!

Reply 647

liviaaa

The paper's sooooo long though, I would say about 80% of things will come up.. :/

Any predictions for the 6 marker?

Reply 648

emmaf

Can someone simply explain immunological response as a way of comparing the relationship between species please? :]

Reply 649

SmithytheDrummer

Original post by mithunaa

thanks!!

My teacher did mention it once, you only need to know that it has a higher affinity for oxygen than normal haemoglobin so it is stored in the muscles and released when p(O2) is low. I think the only context it could come in is as comparisons between haemoglobin and myoglobin dissociation graphs :smile:

Reply 650

Aimo_1

More precipitate produced, more closely related

Antibodies will recognise the antigen that is injected + produce more antibodies, more antigen-antibody complexes that form a precipitate

Reply 651

Stratos

Original post by kingsmod1

not much u can revise, just remmber the booj, have a gd exam technique on data and stuff, the rest is really experience and stuff. practice paper etc.

Yeah biology is definitely all about the exam technique, they don't care about my knowledge, mainly because I used the "wrong words". Apparently they changed the marking scheme now to mark for concepts instead of "keywords".

Reply 652

iguess

Original post by oHellno

Yeah, the DNA replicates during interphase, that's why the chromosomes appear as the 'X' shape. Originally, it's just one 'strand', one chromatid. After replication, you have two sister chromatids, which are then separated during mitosis.

I'm sorry I just read that, I always thought that chromosomes exist as two chromatids joined in the centre by a centromere, just not visible unless they are dividing? I've always been a bit confused.

Reply 653

EffKayy

Original post by emmaf

Can someone simply explain immunological response as a way of comparing the relationship between species please? :]

What do you mean?
if they're similar?
I think the DNA hybridisation.
Basically you heat two strands to break them apart
then, when they cool down the complementary strands join up i think
The more hydrogen bonds there are = more closely related = more energy required to break the new bonds..

:s

Reply 654

kingsmod1

Original post by Stratos

same thing right lol?

Reply 655

Rahul.S

is every1 ready? going to go over at 5ish......

Reply 656

Aimo_1

Original post by Rahul.S

is every1 ready? going to go over at 5ish......

You gonna be able to get the question paper for this one?

Reply 657

EffKayy

I hate AQA. They are so picky with the markschemes! You just have to hope that your answer isn't in "neutral" (the forbidden hell)

Reply 658

kingsmod1

i have too much experience lol, i cant let the new yr 12 noobs beat me
must get an A lol

and for the mar schemes, grade boundaries are low so its fair
plus answers do most of the time match