AQA AS UNIT 2

  • 0 votes

So what did you guys think of the exam? Anyone that want to put the questions and answers is more than welcome :)

Posted Mon 21st May, 2012 @ 16:04 by Kelly Founds

17 Answers

  • 2 votes

i though it was ok! i was glad there wasn't stuff on haemoglobin!

Answered Mon 21st May, 2012 @ 16:13 by Kirsten
Edited by Kirsten on Mon 21st May, 2012 @ 16:13
  • 2 votes

claire hopkins, I got 2 hours for the time taken for mitosis one, i think thats right... what did everyone else get?

Answered Mon 21st May, 2012 @ 17:54 by Jess G
  • 0 votes

I hated it- too many how science works questions

Im completely gutted because i knew the content inside out :(

Answered Mon 21st May, 2012 @ 16:44 by claire hopkins
  • 0 votes

yeah there was way to many graphs and stuff like that. i think it could have been worse though? :)

Answered Mon 21st May, 2012 @ 16:49 by Louise123
  • 0 votes

I'm glad there was no haemoglabin stuff too, i hate that bit!! :D

Answered Mon 21st May, 2012 @ 16:53 by Jess G
  • 0 votes

Ah thats my fav bit! I just looked on the student room at some of the suggestions for the answers, and it seems I havent done too badly, definetly not getting full UMS though!

what did everyone get for the time taken for mitosis cycle?

Answered Mon 21st May, 2012 @ 16:55 by claire hopkins
  • 0 votes

ahh didnt like itt hope everyoness done well x

Answered Mon 21st May, 2012 @ 17:08 by Edward Pinches
  • 0 votes

yh. I'm so good at the haemoglobin stuff, and knew so much of the content. There were too many how science works and plants questions in my opinion  :(

Answered Mon 21st May, 2012 @ 17:25 by Natasha Naeem
  • 0 votes

I thought it was good, but there were a lot of similar questions on species diversity of the wood/field - i seemed to keep repeating myself

Answered Mon 21st May, 2012 @ 17:51 by Annabel
  • 0 votes

For the name two ways bacteria can become resistant did anyone else put: by vertical and horizontal gene transmission? :S

Answered Mon 21st May, 2012 @ 18:57 by Beth
  • 0 votes

thats what i wrote Beth

 hope its right :)

Answered Mon 21st May, 2012 @ 19:29 by Maryam
  • 0 votes

what did you guys get for the last question? I'm not sure why, but i found it  dodgy :/ besides that question, i think the paper was relatively straight forward 

Answered Mon 21st May, 2012 @ 19:45 by Meeral
  • 0 votes

I know I got the cellulose one wrong

Answered Mon 21st May, 2012 @ 19:46 by Azhar
  • 0 votes

Think it was definitely different t many of the past papers a lot of HSW and the beggining 3 or 4 questions were difficult to get into but got easier after that. Liked the 6 mark tissue fluid question

All in all not what I expected but certainly not excessively difficult.

Katiehh **  

Answered Tue 22nd May, 2012 @ 13:07 by Katie
  • 0 votes

was the one where bacteria become resistant not; selection and mutation? :S x

Answered Tue 22nd May, 2012 @ 16:04 by Emily Matthews
  • 0 votes

their wasso much to put for the bacteria things hope the examinars are bnot too specific... the exam was certainly different to the past papera though **

Answered Tue 22nd May, 2012 @ 19:54 by Edward Pinches
  • 0 votes

hey you guys here is an unofficial mark scheme for the AQA unit 2 biology AS paper

**

I found this so people can have a  look at it n c if they can get da marks! Hope every1 does well

1)

a) Diffusion. (1 mark)

b) Thin so short diffusion pathway; large surface area (2 marks)

c) A collection of tissues joined to serve a common/specific function. (1 mark)

d) Diffusion; through stomata; diffusion gradient set up(3 marks)

2)

a) The sugar beet had: (4 marks)

Larger leaves; more surface area for photosynthesis

Larger root; allows more sugar storage/more water storage for photosynthesis.

b) How does the farmer profit? (more answers) (1 mark)

More rapid growth in a shorter time;
saves on fertilisers;

c) How would growing the sugar beet affect the diversity of the sugar roots?
(2 marks)

Grown on large scale;
using the same specific allele;
for more yield of sugar (in shorter time);
(so) diversity reduced;

3) a) Monomers of cellulose (1 mark)

Beta glucose

b) What bond is shown? (1 mark)

Glycosidic

c) What group is Z?

OH/Hydroxyl

d) 2 reasons - Differences between cellulose and starch (2 or 4 marks?)

Starch is made up of alpha glucose; but cellulose beta
starch forms purple complex with iodine; cellulose doesn't form colour;
storage role for starch; structural role for cellulose;
starch has flexible chains; cellulose had straight chains;
starch forms helix; cellulose forms microfibrils

e) Describe structure of cellulose related to function
(2 marks)

long straight chains;
can form microfibrils;
provide rigidity to cell walls;
so they resist osmotic pressure;
held together by hydrogen bonds;
difficult to break bonds;
resists digestion / enzyme activity


4)

a) How do you know this is a polymer? (1 mark)

Joined by many nucleotides / has sugar phosphate backbone / units are repeating

b) Name the molecules.
(Don't remember the order) (3 marks)

Hydrogen bonds
Deoxyribose/Pentose Sugar (the pentagon)
Phosphate (circle)

c) Adenine; Guanine & Cytosine; 16 and 16 each (I think?) (2 marks)

d) Minimum number required

51*3 = 153

e) Introns / junk DNA.

5) a) Why is mitosis essential?


Growth;
Quick cell restoration/repair/regeneration;
asexual reproduction;

b) Stage the two stages in A and B
Ambiguous - I believe they'll be generous.

A -

Prophase; because the chromosomes were condensed and visible

OR

Metaphase; chromsomes were lining up in the equator

B-

Anaphase; chromosomes move to the opposite ends of the cell.

b) 2 hours. Interphase was 90%. 100-90 = 10%. 10% of 20 hours is 2.



6)
Index of diversity questions

a 1.285-1.3

b) Would the index of diversity for the wheat field be less or more? (2 marks)

less;
every species apart from oak aphids had a lower number or organisms than the organisms found in the wood;
many species have 0 organisms;

c) A journalist mentioned that farming reduces the diversity. (2 marks)

No - farming wasn't mentioned;
yes - farmers clear out woodland/other plants to make room for wheat fields;

d) How would shrubs help? (2 marks)

Increase diversity;
more habitats;
more food sources;

7)

a) Kingdom / Phylum / Class (1 mark)

b) Family

c) (2 marks)

Standard deviation measures variation;
if overlap, whether due to chance/coincidence

d)

Courtship identifies members of same species;
male species different colour to other male species;
likewise for female;

e) The question of Protein sequence.

Compared same protein;
same species will have similar base sequences
DNA Hybridisation;
more hydrogen bonds form;
more heat required indicates relationship;
amount of precipitate from both species indicates relationship

8) a) Explain the changes in the graph (3 marks)

(Xylem pressure low during the night) as stomata closed and there’s less transpiration;
(During day it increases) because rate of water movement increases;
because of more sunlight;
This puts the water column under pressure so the xylem is drawn in so diameter is reduced

b) Why are the pressure values negative? (1 mark)

Transpiration pull/xylem pulled in by tension

0)

a) Explain why the artery has the thickest wall? (1 mark)

Artery has thicker walls because pressure is higher.

b) Why is the thickness of the aorta different every time?
(3 marks)

Different surges in pressure;
streches;
recoils;

c) Which showed the greatest variation in wall thickness? (2 marks) ***** of a question - ambiguous.

Aorta; greatest (difference in) standard deviation

Pulmonary veins beacuse the standard deviation for that was highest relative to what the actual mean value was.

d) Explain the formation of tissue fluid (6 marks)

At (arteriole) end of capillary;
Hydrostatic / blood pressure;
Forces out soluble / small molecules;
And water;
Protein remains in blood / plasma;
Molecules too large;
More negative / lower water potential at (venule) end;
Water drawn in by osmosis / diffuses in;
lymphatic system collects excess tissue fluid;
Some fluid/lymph returned to blood by lymphatic system;


10) a) i) Why were the bacteria incubated at 35 degrees? (1 mark)
Similar temperature to body; optimum temperature for bacterial growth.

a) ii) Why was the same amount of bacteria used?
(1 mark)

So you can compare / there'd be more bacteria at the end for different concentrations / decreases validity / results affected

b) i) Why was a control used? (1 mark)

To show that it was only the antibiotic that affected the results

ii) Describe the changes shown on the graph (2 marks)

Rapid decrease up to 5; slight decrease from 5-10; steady but slow decrease from 10-50; extremely slow decrease/levels off from 50-100

iii) The scientists concluded that 50 micrograms was the most efficient concentration. Do you agree?
(3 marks)

Correlation doesn't mean causation;
may be other factor involved;
graph supports this because most amount of bacteria were killed then;
not much difference from above 50 so can save on cost/less risk of resistant bacteria replicating (?);


c) How does bacteria develop resistance? (2 marks)

Random mutation;
Gene transmission

d) Why were the people similar ages

Increases reliablity / more age representitive / affects different ages in different ways

e) The scientists said that taking antibiotics was the right thing to do. Does the information in b c and d support this? (4 marks) Really weird question.

No -

Could wipe out competition and leave resistant strain;
strain divides and gives genes via vertical gene transmission;
there wasn't much difference between the volunteers in 2 months;
both values were the same in 3 months;
antibiotic testing showed that there was still 40% of bacteria despite 100% concentration of antibiotics

Yes -

antibiotics destroy bacteria anyways and can reduce risk of heart disease;



Predicted grade boundaries

70/85 - 140 UMS
60/85 - A
55/85 - B
49/85 - C
44/85 - D

Answered Fri 25th May, 2012 @ 19:58 by Braniac