Year 12s: what will be the first way you research your future options? >>

OCR Biology A Exam Thread (Breadth - May 26, 2016 and Depth - June 7, 2016)

Scroll to see replies

Reply 640

DoubleDoors

Original post by Jitesh

Can sucrose pass a partially permeable membrane??

By facilitated diffusion or active transport only as it is a polar molecule.

Reply 641

xxxtentacion..

Original post by 4nonymous

Pretty much and just recapping topics that I don't understand very well

Ah sehr interessant...I'm clueless as to how I should revise

Reply 642

Astro_Joe

As far as I'm aware, W was the sucrose solution, and Z was the vacuolar membrane due to there being another line that identified the vacuole itself.

What I got for the potato question was:

- Plot a graph of change in mass (y axis) against sucrose concentration (x axis)
- Draw line of best fit through points
- Where the line intersects the sucrose concentration axis, this is the sucrose concentration of the potato tuber cell.
- Student should then compare with data values in literature (etc.) to find corresponding water potential.

Reply 643

User1452521

Original post by DoubleDoors

By facilitated diffusion or active transport only as it is a polar molecule.

Which question was this? Can't remember haha

Reply 644

ImagineCats

Jfc I didn't get any of these answers! What the heeeeeelllll! I revised so hard. So angry man

Reply 645

Synonym

that test messsed me up ..... big time

Reply 646

ImagineCats

Original post by DoubleDoors

By facilitated diffusion or active transport only as it is a polar molecule.

When did any of this stuff even come up in the exam????? I didn't think about diffusion or active transport or anything ARGH

Reply 647

Jitesh

Original post by snickercell

it didn't go through the membrane, it went through the cellulose cell wall because the cell membrane was moved away form the cell wall as the cell plasmolysed which left the area for the sucrose solution to enter as the cell wall has gaps in it.....I think? At least that's what I thought

Oh that sounds right actually!
My mistake!!

Reply 648

mali473

Original post by ImagineCats

Jfc I didn't get any of these answers! What the heeeeeelllll! I revised so hard. So angry man

Tell me about it. I revised so so hard but my answers are completely different :/

Reply 649

TH3-FL45H

Original post by Jitesh

Oh what did you put for ytour maths questions? Word on the street is that you're good at maths :biggrin:

Where'd you hear that?

6600% increase in oxygen
1005 cm^3
28% guanine

Were there any other maths questions?

Reply 650

Mudas

Original post by Astro_Joe

Sounds good :smile:

I said do more readings between the values 0.2 and 0.3 to determine the concentration of sucrose where the change in mass is zero rather than plot a calibration curve. Do u think this would be accepted?

Reply 651

fteam

x=cell wall
y=plasma membrane as during plasmolysis the plasma membrane is drawn away from cell wall
z=tonoplast/vacoule as they never made that clear so could allow either.

The questions 21ai) was there was no consistency of sucrose concentration (from table it went from 0.4 to 0.45 where as throughout it was a difference of 0./1)
the second answer was size\amount of potato disc was not stated or controlled.

21aii) The question where you explain how it shows the water potential within the potato discs. You had to use the figures and explain that the percentage decreased in mass as concentration increased as concentration of sucrose increased so therefore higher water potential was in potato and by osmosis water left potato sacs(whatever they called them) resulting in decrease of mass of potato disc.

Guanine was 28% method= 22x2=44
100-44/2=28

The question based upon red blood cells lacking cell content answer was: increased surface area to volume ration and therefore maximum level of 02 can be transported to respiring tissues.

Then the one about why red blood cells never used up 02 was because they never contained double membrane bound organelles such as mitochondria which uses 02 for aerobic respiration. (dont know if im correct)

The question about the conservation when asking about small groups were isolated advantages where:
if a disease arise will not wipe out whole population
isolated therefore protected from predators and human hunted rhinos.

Another question was filling in missing gaps went in order like this : KINGDOM=ANIMALIA
Phylum, Class, Order, Fishes, Genus, Species=(in the question it said D.S... it was to copy the s part of name)
the second part to questions was why is binomial system helpful this was because it avoids confusion across the world when classifying species.

Last question was= bohr effect.

ii) active respiring tissues have lower saturation of 02 because aerobic resp. takes place releasing more co2 at faster rate which in return reacts with water to form carbonic anhydrase which then dissociates to form h+ ions causing haemoglobin to unfold as the bonds are broken such as hydrogen and ionic and 02 is released. Or active tissues have low p02 so Hhb dissociates to release 02.

cant remember the letters for the question after.

last question was based on mass flow. Cotransportation occurs where sap is actively loaded companion cell then diffuse through plasmodesmata, at top of sieve tube elements theres high hydrostatic pressure therefore creates a pressure gradient and moves along gradient towards sink where they are unloaded. Mention flow of sap in one direction to gain mark for mass flow.

Reply 652

alevelexams2016

I had 3 for each one as well, sounds about the same to what I got

Reply 653

ImagineCats

Original post by mali473

Tell me about it. I revised so so hard but my answers are completely different :/

This is so frustrating :frown:

I don't think I got into year 13 at this rate I've screwed it all up! I wanted to do genetics at uni but NO this exam will screw it all up aoishf;weoht;awoitaw;otslgn\seliuthlkjnt

Reply 654

User1452521

Original post by TH3-FL45H

Didnt even know tonoplast was a thing lol. I just put it was a vacuole

X-cell wall
Y-plasma membrane
Z-vacuole

W-air (had no idea)

I put intracellular fluids i.e. amino acids for W, i had no idea either!

Reply 655

Mudas

For the question regarding what was located in W, it was the sucrose solution (Slightly diluted however). This is because the cell wall is permeable, which means as the plasma membrane withdraws the sucrose solution can pass through the cell wall and fill the gap.

Reply 656

ImagineCats

Looks like I'm doing geography at uni lol

Reply 657

hashman

Original post by torilee

That's a good point, although that other label might have been pointing at the cell sap?

the answer was tonoplast

Reply 658

gahdam

Original post by ImagineCats

This is so frustrating :frown:

I don't think I got into year 13 at this rate I've screwed it all up! I wanted to do genetics at uni but NO this exam will screw it all up aoishf;weoht;awoitaw;otslgn\seliuthlkjnt