AQA a level biology paper 2 // 13th June 2019 // unofficial mark scheme LIST

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onlyangel7
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I know there’s been a thread made previously but I thought I’d try and make a list of some answers based on that so they’re all in one place
Fully aware some are probs wrong but I’ll edit it with peoples suggestions, let me know (but be nice haha). I’ve also not been able to remember all the questions and it’s not in order, so please let me know if you remember any other questions and I’ll add them on


Succession 4 marker
- Pioneer species colonises, adapted to hostile conditions
- Changes abiotic conditions as broken down by saprobionts, creates soil/humus which retains water
- Means next species can colonise as conditions less hostile, die and decomposed by saprobionts, more humus
- Repeats. At any stage, new species can be introduced that makes conditions less favourable for previous species, outcompetes them.
- Eventually climax community, most stable the ecosystem can support

4 marks worth of trophic maths
- There was a 2 marker, I got 0.155%
- 2 marker was to do with the zebras, it was 177? Not sure

Stem cell/haemoglobin question:

Why does substitution mutation change structure of (insert protein name)? (3 marks)
- Substitution is one base swapped for another
- This changes the base triplet that that base was part of, the triplet then coded for a different amino acid
- Different amino acid changes primary structure of protein, which determines the tertiary structure of the protein
- Tertiary structure of the protein is therefore changed

Why is bone marrow transplant an effective long term solution? (2/3 marks)
- Stem cells specialise into red blood cells, caused by expression of certain genes
- These cells can then divide by mitosis into more healthy red blood cells, replace unhealthy/sickle shaped red blood cells.

Is gene therapy better? Evaluate (2/3 marks)
- Uses patients own cells, less chance of rejection as they are their own antigens
- However stem cell transplant from sibling, similar genes so similar antigens, low chance of rejection anyway

IAA:
2 marker on why remove shoots
- IAA is made in the shoots of plants, in highest concentration here

Why keep lid closed (2 marks)
- Prevent contamination by bacteria, compete for glucose etc (?)
- Stop evaporation of glucose/water (?)
- Keep oxygen concentration constant in all Petri dishes (?)
- Block light from reaching IAA (?)

Why add glucose (2 marks)

3 marker on what if roots instead/describe and explain results
- higher concentration of IAA means greater increase in shoot length
- caused as IAA stimulates cell elongation in shoots
- but in roots it inhibits cell elongation, so if roots were used higher concentration would mean less growth

1 marker on serial dilution

Stupid pH graph 4 marker
- I think I put that contraction had less force in both rabbits and mice at 12 and 22, but not at 32 so pH does decrease muscle contraction at lower temperatures but not at higher
- I’ve seen people say that the fact a stats test wasn’t used would get you a mark


Why decreased calcium ions inhibits muscle contraction (3 marks)
- calcium ions bind to a protein attached to tropomyosin, cause it to change shape, pull tropomyosin out of actin-myosin binding site exposing it
- so that myosin heads can bind, forms actin myosin cross bridge, pull actin over myosin causing muscle to contract as sarcomere shortens
- so if calcium ions are decreased, tropomyosin blocks binding sites, less contraction
- calcium also activates ATP hydrolyse (ATP -> ADP + Pi), energy used for contraction, so if less calcium then less energy

Chromatography questions:
Why use pencil instead of ink? (1 mark)
- Ink would dissolve in solvent and pigments separate as solvent spreads up chromatogram

Method to separate pigments (2 marks):
- Place chromatogram in beaker of solvent, solvent shouldn’t go above pencil line
- Solvent moves up paper and carries different pigments at different rates

Rf value (1 mark)
- Will be a range, I got 0.608 but could be slightly higher/lower depending how you measured

Why is different coloured pigments in leaves advantageous? (1/2 marks)
- Can absorb different wavelengths of light

Inheritance question:

Why is body colour not on X chromosome

Why you know grey is dominant(? I think)

3 marker on find phenotypes
- I got 1:1:1:1 ratio

2 marks hardy Weinberg equation
48%

Role of glucagon (2 marks)
- Produced in alpha cells in islets of langerhans in pancreas
- Activates glycogenolysis and gluconeogenesis, decreases rate of respiration in cells

Role of insulin (2 marks)
- Increases permeability of membrane to glucose, more uptake
- Activates glycogenesis

Why does inhibiting adenylate Cyclase reduce glucose concentration (3 marks)

5 marker on estimating population (sunningdew or whatever)

Why is it advantageous for sunningdews to digest insects in nutrient deficient soil (2 marks)

Tick box 1 marker on LDR chemicals used
- bottom one

2 marker on photoionisation
Light hits chlorophyll, electrons become excited, leave chlorophyll and move to higher energy level, move down ETC

What is a DNA probe (2 marks)
- single stranded base sequence complementary to desired gene with label attached

How is DNA cut (2 marker)
- Restriction endonuclease, cuts DNA at specific palindromic recognition sequences (recognition sites)

How long is DNA 2 marker
- I got 3.42

Suggest why there are more bands than just 4 2 marker

Gel electrophoresis 1 marker on which volunteers
- I got 3,4,5

Application 15 marker:
3 marker on why myelin sheath being broken causes muscle paralysis

3 marker on why Huntington can lead to irregular heartbeat

3 marker on how single stranded DNA reduces Huntingtin:
- Single stranded DNA binds to mRNA transcribed from Huntingtin gene
- This means mRNA is unable to bind to the ribosome as it is blocked
- This prevents translation from occurring, so the Huntingtin protein is not translated, there is therefore less of it

2 marker on why trials don’t show cure
- Only over 4 months
- Only 36(?) individuals

2 marker on why injected into spine and not taken orally
- would be digested by digestive enzymes
- short diffusion pathway to cells where it would be most effective as Huntingtin produced here, drug has effect quicker

2 marker on why epistasis causes Huntington’s to appear later in life
Last edited by onlyangel7; 2 years ago
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AliRiz1
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I got 177 as well for the zebras question.
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Jademorgan1
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Question after dna probe one was how is dna cut
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AliRiz1
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The answer was restriction enzymes at specific palindromic sites called restriction sites, leaves DNA with sticky ends, right?
(Original post by Jademorgan1)
Question after dna probe one was how is dna cut
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Jademorgan1
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Yah that’s what I put
(Original post by AliRiz1)
The answer was restriction enzymes at specific palindromic sites called restriction sites, leaves DNA with sticky ends, right?
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onlyangel7
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I’ve added it on

(Original post by Jademorgan1)
Question after dna probe one was how is dna cut
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Mcpatel24
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keep lid closed to prevent contamination and so that just enough oxygen can get not too high as it could become dangerous
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onlyangel7
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Added this too
(Original post by Mcpatel24)
keep lid closed to prevent contamination and so that just enough oxygen can get not too high as it could become dangerous
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blueoreo
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Question about why the tips were removed - something about this is where cell elongation occurs did not want to bias experiment by including rest of plant which may have larger SA to increas experiment?
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Joe Furn
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(Original post by onlyangel7)
I know there’s been a thread made previously but I thought I’d try and make a list of some answers based on that so they’re all in one place
Fully aware some are probs wrong but I’ll edit it with peoples suggestions, let me know (but be nice haha). I’ve also not been able to remember all the questions and it’s not in order, so please let me know if you remember any other questions and I’ll add them on

I have about 70 marks worth here, the paper was out of 91 so I’m definitely missing some questions

Succession 4 marker
- Pioneer species colonises, adapted to hostile conditions
- Changes abiotic conditions as broken down by saprobionts, creates soil/humus which retains water
- Means next species can colonise as conditions less hostile, die and decomposed by saprobionts, more humus
- Repeats. At any stage, new species can be introduced that makes conditions less favourable for previous species, outcompetes them.
- Eventually climax community, most stable the ecosystem can support

3 marks worth of trophic maths
- There was a 1 marker, I got 0.155%
- 2 marker was to do with the zebras, it was 177? Not sure


IAA: 2 marker on why remove shoots

Why keep lid closed (2 marks)
- Prevent contamination
- Stop evaporation
- Keep oxygen concentration constant in all Petri dishes

Why add glucose (2 marks)

3 marker on what if roots instead/describe and explain results
- higher concentration of IAA means greater increase in shoot length
- caused as IAA stimulates cell elongation in shoots
- but in roots it inhibits cell elongation, so if roots were used higher concentration would mean less growth

1 marker on serial dilution

Stupid pH graph 4 marker
- I think I put that contraction had less force in both rabbits and mice at 12 and 22, but not at 32 so pH does decrease muscle contraction at lower temperatures but not at higher
- I’ve seen people say that the fact a stats test wasn’t used would get you a mark


Why decreased calcium ions inhibits muscle contraction (3 marks)
- calcium ions bind to a protein attached to tropomyosin, cause it to change shape, pull tropomyosin out of actin-myosin binding site exposing it
- so that myosin heads can bind, forms actin myosin cross bridge, pull actin over myosin causing muscle to contract as sarcomere shortens
- so if calcium ions are decreased, tropomyosin blocks binding sites, less contraction
- calcium also activates ATP hydrolyse (ATP -> ADP + Pi), energy used for contraction, so if less calcium then less energy

Inheritance question:

Why is body colour not on X chromosome

Why you know black is recessive(? I think)

3 marker on find phenotypes
- I got 1:1:1:1 ratio

2 marks hardy Weinberg equation
48%

Insulin - role of glucagon (2 marks)

Why does inhibiting adenylate Cyclase reduce glucose concentration (3 marks)

5 marker on estimating population (sunningdew or whatever)

Why is it advantageous for sunningdews to digest insects in nutrient deficient soil (2 marks)

Tick box 1 marker on photosynthesis
- bottom one

2 marker on photoionisation
Light hits chlorophyll, electrons become excited, leave chlorophyll and move to higher energy level, move down ETC

What is a DNA probe (2 marks)
- single stranded base sequence complementary to desired gene with label attached

How is DNA cut (2 marker)
- Restriction endonuclease, cuts DNA at specific palindromic recognition sequences (recognition sites)

How long is DNA 2 marker
- I got 3.42

Suggest why there are more bands than just 4 2 marker

Gel electrophoresis 1 marker on which volunteers
- I got 3,4,5

Application 15 marker:
3 marker on why myelin sheath being broken causes muscle paralysis

3 marker on why Huntington can lead to irregular heartbeat

3 marker on role of epistasis on Huntington’s being later in life

2 marker on why trials don’t show cure
- Only over 4 months
- Only 36(?) individuals

2 marker on why injected into spine and not taken orally
- would be digested by digestive enzymes
- short diffusion pathway to cells where it would be most effective as Huntingtin produced here, drug has effect quicker

2 marker on something else
Role of glucagon question I put glucagon is made in the islets of Langerhans initiates gluconeogenesis which make glucose from non carbohydrates
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Jademorgan1
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Idk about that lid one like I don’t personally think it’s to do with the gasses in the air or bacteria since they’re not really affecting the experiment like I get when people are saying about comp but bacteria would use such little glucose and many are anaerobic anyway and then about the gases I think since they’re in the same place it would make any different since if there was no lid the conc of o2 and co2 in air isn’t going to change I think it’s more about the evaporation of either the water from the solution/the iaa solution
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Jademorgan1
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*not to do with the gasses
(Original post by Jademorgan1)
Idk about that lid one like I don’t personally think it’s to do with the gasses in the air or bacteria since they’re not really affecting the experiment like I get when people are saying about comp but bacteria would use such little glucose and many are anaerobic anyway and then about the gases I think since they’re in the same place it would make any different since if there was no lid the conc of o2 and co2 in air isn’t going to change I think it’s more about the evaporation of either the water from the solution/the iaa solution
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Ems000
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Quiet a few of my friends and myslef put about the lid blocking light preventing the IAA from unevenly distributing and causing cell elongation to curve the shoot making it hard to judge the change in length. Idk if it’s right but I don’t understand the answers about bacteria or oxygen because the bacteria would use minimal glucose and the oxygen concentration would be the same as they were all in the same room anyway. I think the evaporation one is likely the answer
(Original post by Jademorgan1)
Idk about that lid one like I don’t personally think it’s to do with the gasses in the air or bacteria since they’re not really affecting the experiment like I get when people are saying about comp but bacteria would use such little glucose and many are anaerobic anyway and then about the gases I think since they’re in the same place it would make any different since if there was no lid the conc of o2 and co2 in air isn’t going to change I think it’s more about the evaporation of either the water from the solution/the iaa solution
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onlyangel7
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(Original post by blueoreo)
Question about why the tips were removed - something about this is where cell elongation occurs did not want to bias experiment by including rest of plant which may have larger SA to increas experiment?
(Original post by Joe Furn)
Role of glucagon question I put glucagon is made in the islets of Langerhans initiates gluconeogenesis which make glucose from non carbohydrates
Added these
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onlyangel7
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(Original post by Jademorgan1)
Idk about that lid one like I don’t personally think it’s to do with the gasses in the air or bacteria since they’re not really affecting the experiment like I get when people are saying about comp but bacteria would use such little glucose and many are anaerobic anyway and then about the gases I think since they’re in the same place it would make any different since if there was no lid the conc of o2 and co2 in air isn’t going to change I think it’s more about the evaporation of either the water from the solution/the iaa solution
(Original post by Ems000)
Quiet a few of my friends and myslef put about the lid blocking light preventing the IAA from unevenly distributing and causing cell elongation to curve the shoot making it hard to judge the change in length. Idk if it’s right but I don’t understand the answers about bacteria or oxygen because the bacteria would use minimal glucose and the oxygen concentration would be the same as they were all in the same room anyway. I think the evaporation one is likely th
I’ve added some different suggestions too, really not sure what the answer is haha
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maitraa12
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think the last 2 marker was about epigenetics causing Huntington's symptoms when a person gets older or something x
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Azeee
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(Original post by onlyangel7)
x
Hey thanks for your post - I've listed some questions you've missed and also some comments about questions you've mentioned:

- You sure the productivity trophic question wasn't 2 marks (so 4 in total?)
- Chromatography - why pencil is used instead of ink (1 mark) - i wrote cos it would blot the paper as the solvent spread up or whatever
- Chromotography - how are different pigements seperated (2 marks) - solvent moves up paper and carries different pigments at different rates, think i might only get 1 mark for that tbh
- Chromotography - there was a 1-2 marker on why different pigments in chlorophyll is advantageous (I put different wavelengths of light can be absorbed so more light energy for photosynthesis)
- Regarding role of insulin, I stated that it increased permeability of membranes to glucose so that there's more uptake - I think I wrote this cos the question mentioned something about how it binds to receptors on cells or something
- i think there was a 2 marker question above in the space above the 3 marker for the genetics question, but idk what it was?
- question on substitution of base and how it changes shape of protein (think the context was haemoglobin, 3 marker)
- Then more questions on bone marrow transplant, why its a long term solution (2 marks) and why the virus injection might be better (2 marks)
- There were a bunch of boxes for question that asked what chemicals are used in light dependent photosynthesis - bottom box was correct (1 mark)
Last edited by Azeee; 2 years ago
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onlyangel7
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Thank you so much! This has given me a confidence boost haha, you’ve included questions I’d forgotten about that I think I got right, I got similar answers to a lot of the questions. I’ve added them on
(Original post by Azeee)
Hey thanks for your post - I've listed some questions you've missed and also some comments about questions you've mentioned:

- You sure the productivity trophic question wasn't 2 marks (so 4 in total?)
- Chromatography - why pencil is used instead of ink (1 mark) - i wrote cos it would blot the paper as the solvent spread up or whatever
- Chromotography - how are different pigements seperated (2 marks) - solvent moves up paper and carries different pigments at different rates, think i might only get 1 mark for that tbh
- Chromotography - there was a 1-2 marker on why different pigments in chlorophyll is advantageous (I put different wavelengths of light can be absorbed so more light energy for photosynthesis)
- Regarding role of insulin, I stated that it increased permeability of membranes to glucose so that there's more uptake - I think I wrote this cos the question mentioned something about how it binds to receptors on cells or something
- i think there was a 2 marker question above in the space above the 3 marker for the genetics question, but idk what it was?
- question on substitution of base and how it changes shape of protein (think the context was haemoglobin, 3 marker)
- Then more questions on bone marrow transplant, why its a long term solution (2 marks) and why the virus injection might be better (2 marks)
- There were a bunch of boxes for question that asked what chemicals are used in light dependent photosynthesis - bottom box was correct (1 mark)
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Azeee
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Likewise : )
(Original post by onlyangel7)
Thank you so much! This has given me a confidence boost haha, you’ve included questions I’d forgotten about that I think I got right, I got similar answers to a lot of the questions. I’ve added them on
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beditness
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Predictions on grade boundaries guys?
I felt the exam was reasonable but this is relative to the specificity of the mark scheme. Similar to 2017 Gb imo, if not lower
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