AQA A Level Biology Paper 2 - 11th June 2018 Unofficial Markscheme

These are my answers. Do not worry if yours isn't exactly this. Rehaan :smile:

Rubisco Question
1.1
Heat stress affects light independent as less ATP and NADPH made from light dependent so less RuBP generated and less GP reduced to TP.
1.2
? (Very similar to above)
1.3
Stroma of Chloroplasts (in cytoplasm of cell).
1.4
At higher temp. Rubisco activate activity decreases whereas Rubisco activity/rate proportional to higher temp.
However, as Rubisco activase rate decreased probably does affect Rubisco (despite higher temp meaning faster rate).
No stats tests done so cannot see if difference is significant.
Rubisco activity could be due to other enzyme influence.
Isolated enzymes so affect my be different as not in chloroplast environment
Scale of results - only 50 for Rubisco but 60 for Rubisco Activase

Tumour
2.1
Second box

2.2
TWO mutated alleles (as recessive)
So alters DNA base sequence of tumour suppressor gene
So non-functional tumour suppressor gene as affects translation SO uncontrolled mitosis.

2.3
= 2^84 = 1.934281 x 10^25

Respirometer
3.1
Probably a list:
1. Allow respiration rates of yeast to stabilise.
2. Pressure expansion/equilibriate

3.2
Yeast aerobically respires and takes in oxygen/oxygen also taken in by "alkaline propygol" SO eventually will all be anaerobic respiration
Carbon dioxide released/also released via anaerobic respiration (as yeast).
Increases hydrostatic pressure therefore liquid moves down the pressure gradient.

3.3
0.049

Succession
4.1
Split sand dune into grid.
Use random number generator to generate coordinates.
Randomly sample many times.
Calculate % cover/estimate cover.

4.2
Grass is pioneer species so alters abiotic conditions such as wind speed.
Outcompeted and die and form humus.
Thus other species can grow.
Over time trees grow more as climax community forms, passing through many sereal stages.

4.3
Mainly trees that grow so shade so block light from penetrating in/at lower surface

4.4
NPP = GPP - R
Higher NPP as greater GPP so greater chemical energy store as more trees.
GPP greater magnitude than R so counteracts.

Experiment on Urine
5.1
?
Can't remember exact questions but the last one:
1. Na+ and Cl- ions not absorbed SO lower water potential of collecting duct.
2.Thus reduces water potential gradient.
3. As less water diffuses out by osmosis for reabsorption SO more in urine.

Autosomal Linkage
9:3:3:1 Ratio

Dopamine
7.1
1. Wave of depolarisation causes voltage-gated Ca2+ channels to open.
2. Ca2+ ions diffuse in by facilitated diffusion and bind to vesicles containing dopamine (causing movement to membrane).
3. Vesicles fuse with membrane and release dopamine by exoctyosis which diffuses across the synaptic cleft and binds to receptors.
7.2
Complementary shape so binds to opoid (?) receptors
Releasing more dopamine so more action potentials (in post-synpatic).
7.3
Releases Cl- ions which diffuse in and cause hyperpolarisation
So more depolarisation with Na+ ion needed to exceed threshold
So reduces action potentials (as very low/negative) so inhibitory.

Precipitation DNA Question

LP
9.1
Epigenetics (as diet/drinking milk) affects gene expression for lactate/ lactate expressed more
So more enzyme produced so survive and reproduce i.e. natural selection description.
Pass on for "more expression" so increase of frequency so directional.

OR
Those who drank more milk obtained more nutrients so more growth
So those without milk at breeding disadvantage/selected against (as malnourished)
So those that grow more survive and reproduce and thus directional selection.
9.2
?
9.3
Addition mutation (could be deletion)
Causing frame-shift so indirectly affects lacase gene

OR
Mutation in transcriptional factor for lactase gene
So permanently expressed/activated.

Red-Green Blindness

(edited 5 years ago)

Reply 1

GCShElpme

12

For 1.4, I suggested that because the enzyme activity was isolated/isolated enzymes were used, enzymes could behave differently in chloroplasts. I've asked my teacher, and having seen the paper, she thinks that this will be an acceptable answer! :smile:

Reply 2

Cbeeston

6

Don’t agree with the division one. My answer was 1+2^83. There were 84 total divisions but You have to consider there is only 1 cell to begin with.

Reply 3

Cbeeston

6

Don’t agree with the division one. My answer was 1+2^83. There were 84 total divisions but You have to consider there is only 1 cell to begin with. Think my final answer was something like 9.67 x10^24 or something like that

Reply 4

GCSEStudent903

OP

13

Original post by GCShElpme

For 1.4, I suggested that because the enzyme activity was isolated/isolated enzymes were used, enzymes could behave differently in chloroplasts. I've asked my teacher, and having seen the paper, she thinks that this will be an acceptable answer! :smile:

Sure, good enough point! :smile:

Reply 5

GCSEStudent903

OP

13

Original post by Cbeeston

Don’t agree with the division one. My answer was 1+2^83. There were 84 total divisions but You have to consider there is only 1 cell to begin with. Think my final answer was something like 9.67 x10^24 or something like that

Okay and?

You have to do 1x not 1+??

You start with 1 cell SO 1 times. If 2 cells two times. If 50 cells 50 times.

Reply 6

username3314458

10

did anyone get 18% for the hardy weinburg q??

Reply 7

GCSEStudent903

OP

13

Original post by Maha1999

did anyone get 18% for the hardy weinburg q??

You didnt square root it :smile:

Reply 8

b.r.2018

10

These are my calc answers from my calculator memory in order of question number:

1.93×10^25
4.91×10^-6
296826
20400
18

Reply 9

Hi21042000

3

What did everyone get for hardy Weinberg think I got 44 or 46 can’t remember

Reply 10

Cbeeston

6

Original post by GCSEStudent903

You didnt square root it :smile:

My answer for hardy weinberg was 43%

exactly

Original post by GCSEStudent903

These are my answers. Do not worry if yours isn't exactly this. Rehaan :smile:

Rubisco Question
1.1
Heat stress affects light independent as less ATP and NADPH made from light dependent so less RuBP generated and less GP reduced to TP.
1.2
? (Very similar to above)
1.3
Stroma of Chloroplasts (in cytoplasm of cell).
1.4
At higher temp. Rubisco activate activity decreases whereas Rubisco activity/rate proportional to higher temp.
However, as Rubisco activase rate decreased probably does affect Rubisco (despite higher temp meaning faster rate).
No stats tests done so cannot see if difference is significant.
Rubisco activity could be due to other enzyme influence.

Tumour
2.1
Second box

2.2
TWO mutated alleles (as recessive)
So alters DNA base sequence of tumour suppressor gene
So non-functional tumour suppressor gene as affects translation SO uncontrolled mitosis.

2.3
= 2^84 = 1.934281 x 10^25

Respirometer
3.1
Probably a list:
1. Allow respiration rates of yeast to stabilise.
2. Pressure expansion/equilibriate

3.2
Yeast aerobically respires and takes in oxygen/oxygen also taken in by "alkaline propygol"
Carbon dioxide released/also released via anaerobic respiration (as yeast).
Increases hydrostatic pressure therefore liquid moves down the pressure gradient.

3.3
0.049

Succession
4.1
Split sand dune into grid.
Use random number generator to generate coordinates.
Randomly sample many times.
Calculate % cover/estimate cover.

4.2
Grass is pioneer species so alters abiotic conditions such as wind speed.
Outcompeted and die and form humus.
Thus other species can grow.
Over time trees grow more as climax community forms, passing through many sereal stages.

4.3
Mainly trees that grow so shade so block light from penetrating in/at lower surface

4.4
NPP = GPP - R
Higher NPP as greater GPP so greater chemical energy store as more trees.
GPP greater magnitude than R so counteracts.

Experiment on Urine
5.1
?
Can't remember exact questions but the last one:
1. Na+ and Cl- ions not absorbed SO lower water potential of collecting duct.
2.Thus reduces water potential gradient.
3. As less water diffuses out by osmosis for reabsorption SO more in urine.

Q6?

Q7

Precipitation DNA Question

LP

Red-Green Blindness

Q7 I think was about the dopamine,morphine and pain relief then GABA inhibiting the postsynaptic from sending nerve impulse...something like this I think

There was also one about the expected ratio being different from the observed. The genotype for dwarf and mottled. Then using the table to explain the number of offspring with different phenotypes. Then filing the table on expected and observed phenotypes if the alleles were on a different chromosome.

(edited 5 years ago)

Reply 13

Syedsdad

2

Original post by Cbeeston

Don’t agree with the division one. My answer was 1+2^83. There were 84 total divisions but You have to consider there is only 1 cell to begin with. Think my final answer was something like 9.67 x10^24 or something like that

ur right bro. 9.67x10^24. there was aq like that in bio paper 1. you have to take one off the power

(edited 5 years ago)

Reply 14

Inferno64

3

For 3.2 I'm pretty sure yeast undergoes anaerobic respiration as all of the oxygen was absorbed by the solution. So when CO2 was produced it increased pressure so bubble moved away.

Reply 15

Nannonorange

10

Original post by Inferno64

For 3.2 I'm pretty sure yeast undergoes anaerobic respiration as all of the oxygen was absorbed by the solution. So when CO2 was produced it increased pressure so bubble moved away.

That’s what I put 🙏

Reply 16

EthanolClifton

3

Original post by Cbeeston

Don’t agree with the division one. My answer was 1+2^83. There were 84 total divisions but You have to consider there is only 1 cell to begin with.

The addition of 1 to a number as big as 2^83 makes no difference on the final answer

Reply 17

jamakzai12

4

I was wondering if u guys put for question 7 LP? I was talking about selection pressure, adaptation, genetic mutation, selective reproduction, some directional selection if i remember