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AQA A-level Biology 7402 - Paper 3 - 17th June 2019 Unofficial Markscheme

Thanks for starting an unofficial mark scheme! Just wondering.. but I put down semi lunar valve and not AV valve - is AV correct then? :smile:

Original post by wajopdsjf

Q1.
Ultrafiltration describe process...
Tick Box
Thicker medulla

Q2)
Heart dissection
LEFT atroventricular valve
LEFT ventricle
Precautions...
Scapel (sharp etc)
Gloves (sanitory purposes etc)
Uni directional flow
Describe valves opening and closing
Describe pressure changes and flow of blood

Q3)
Samples of water
Make up KNOWN solutions of water
Measure absorbance of each sample... use colorimeter
Calibration Curve
Use graph to determine cloudiness

Q4)
Caffeine --> Why it increase HR
Mention increase nerve impuleses to medulla oblangata
Increase nerve impulse frequency through sympathetic NS
More Noradrenaline released
More SAN/AVN excitation
More contraction of cardiac muscle

Control:
NO caffeine but sugar
Effect: See whether sugar actually has an affect on increasing HR

Q5)
Anti cancer drug (3marks)
Trexall has a similiar hape/structure to folic acid
Acts as an COMPETITIVE inhibitor
Less E-S complexes formed
Less nucleotides available for DNA replication
Less division by mitosis

STARFISH question...
Choice chamber ... two things kept the same so that they show normal behaviour
PH
Temperature
Coral reef etc
Explain whether either light can be used(3 marks)
Comment on BOTH SD
Effect on each

Maths questions...
Volume of blood (70-78 range)
Sphere question
Hours for starfish... 3 Hours
30030mm^3

Essay (25marks)
Bonding and bonds in organisms
DNA and its use in tech

Help me with questions @evilhomer

Reply 21

CopyThat

12

I think you've overcomplicated the question - im pretty sure it was just a bog-standard enzyme-substrate complex to do with competitive inhibition of the enzyme due to the similar shape of the inhibitor to the substrate

Original post by Alifiahus

I think you’d have to be more specific, I don’t even think competitive inhibition would be accepted? (Unless this is an example of competitive inhibition I’m not sure) There was a methyl group (-CH3) on the diagram, so I wrote that the drug slows down cell division my methylation, the methyl group binds to the promoter region on the DNA molecule, which prevents RNA polymerase from binding, therefore preventing transcription

Reply 22

wajopdsjf

OP

7

Hiya no worries, im not sure but i put av

Original post by science_geeks

Thanks for starting an unofficial mark scheme! Just wondering.. but I put down semi lunar valve and not AV valve - is AV correct then? :smile:

Reply 23

Vfdvf-%

2

I wrote no stats test for every single question including the essay

(Original post by Alifiahus)I think you’d have to be more specific, I don’t even think competitive inhibition would be accepted? (Unless this is an example of competitive inhibition I’m not sure) There was a methyl group (-CH3) on the diagram, so I wrote that the drug slows down cell division my methylation, the methyl group binds to the promoter region on the DNA molecule, which prevents RNA polymerase from binding, therefore preventing transcription

Reply 24

hobicorn

11

I really hope that’s all it is because I just wrote about competitive inhibition.. hhh

Original post by CopyThat

I think you've overcomplicated the question - im pretty sure it was just a bog-standard enzyme-substrate complex to do with competitive inhibition of the enzyme due to the similar shape of the inhibitor to the substrate

Reply 25

wajopdsjf

OP

7

Exactly!

Original post by CopyThat

I think you've overcomplicated the question - im pretty sure it was just a bog-standard enzyme-substrate complex to do with competitive inhibition of the enzyme due to the similar shape of the inhibitor to the substrate

Reply 26

Alifiahus

5

Original post by CopyThat

I think you've overcomplicated the question - im pretty sure it was just a bog-standard enzyme-substrate complex to do with competitive inhibition of the enzyme due to the similar shape of the inhibitor to the substrate

I don’t know I think it would be too much of a coincidence for a methyl group to be on the molecule and the question to not be about how methylation of DNA prevents transcription. Hopefully both answers are acceptable :smile:

Reply 27

science_geeks

15

Original post by wajopdsjf

Hiya no worries, im not sure but i put av

Ah cool, I think generally everyones leaning towards AV valves, but hopefully it shouldn't be too bad because its just 1 mark

Reply 28

Blade Kahtaan

3

While it’s true it had methyl groups, it’s not detaching them and causing them to bind to DNA. I think the fact that they put the substrate and the new molecule next to each other was so that you’d appreciate they have similar structures so would both bind onto the enzyme, which is competitive inhibition

Reply 29

CopyThat

12

Really annoying that they put diagrams in like that one where it's really difficult to tell.

Original post by science_geeks

Ah cool, I think generally everyones leaning towards AV valves, but hopefully it shouldn't be too bad because its just 1 mark

Reply 30

science_geeks

15

Yeah, definitely especially a diagram with only 1 label as well!! It was just really hard to know what is was for certain

Original post by CopyThat

Really annoying that they put diagrams in like that one where it's really difficult to tell.

Reply 31

safiyyahahsan

7

100% was competitive inhibition

Original post by CopyThat

I think you've overcomplicated the question - im pretty sure it was just a bog-standard enzyme-substrate complex to do with competitive inhibition of the enzyme due to the similar shape of the inhibitor to the substrate

Reply 32

Go_Boldly

4

I got 17.4, 73.4, 31, 0.1% , 4.6 and 32016 for the maths questions but I can't remember the questions they're for

Reply 33

Go_Boldly

4

And I went semi-lunar

Reply 34

Yasmin1777

2

Exactly the diagram was so unclear

Original post by CopyThat

**** i thought it was the semi-lunar valve.. it looked quite high up :frown:

Reply 35

Tharris2001

3

Loads of chemicals have methyl groups but it doesn't mean that they inhibit transcription, it is not as simple as a methyl group just detaching from a molecule and then binding to another

Original post by Alifiahus

I don’t know I think it would be too much of a coincidence for a methyl group to be on the molecule and the question to not be about how methylation of DNA prevents transcription. Hopefully both answers are acceptable :smile:

(edited 4 years ago)

Reply 36

YellowYellow2

16

I think I got like 4.8 years for one of the questions

Reply 37

Ismael mahmood

3

Multiple choice was the last box

Reply 38

Alfiepeacock_13

8

Got this too. You had to do log10(3.98x10^11) to find the number of cells and then use the graph to find the age of the tumor. The answer is not 11.6 I don't think

Original post by Khushi.S

I think I got like 4.8 years for one of the questions

Reply 39

YellowYellow2

16

Original post by Alfiepeacock_13

Got this too. You had to do log10(3.98x10^11) to find the number of cells and then use the graph to find the age of the tumor. The answer is not 11.6 I don't think

Yep that is what I did too, I think 11.6 was the Y axis and you then had to read across to the X axis and get 4.8?

AQA A-level Biology 7402 - Paper 3 - 17th June 2019 Unofficial Markscheme

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