UNOFFICIAL MARK SCHEME: AQA A Level Biology 12/06/2017

there was a six marker that went something along the lines of compare and contrast transmission electron microscopes and optical microscopes

Reply 4

Nakatar

a question on improvements to the student's scientific diagram
I think the answer was something along the lines of : have continuous lines, not disjointed (if that even makes sense), and don't shade
idek i probably failed that

Reply 5

Virolite

14

i can post the paper in a bit paper but id rather focus on A2.

Reply 6

Nakatar

there was a question on evolutionary relationships
and a table on levels of classification which we had to fill in
a smaller question on what the scientists disagreed on, relating to the binomial naming system (i think it was to do with the genus?)

im just quickly writing this all down before i forget

Reply 7

Freya.sharpe2900

Why mrna is different to pre mRNA

Reply 8

Adam7789

Tick the box for the ATP Synthase question

Describe the role of phagocytosis in displaying antigens

Describe how presentation of an antigen leads to the secretion of antibodies

State 3 methods the scientists would use to determine the evolutionary relationship between the snakes

Explain the shape of the curves at 50°C and 60°C

Suggest 3 variables the scientists would control

Evaluate the use of the 2,4-D herbicide on wheat and oatcrop/weed

(edited 6 years ago)

Reply 9

biostudent1998

Original post by Amefish

Since I've seen a lot of people asking for the unofficial mark scheme, I thought: why not make a thread? Now, no-one's memory is absolutely perfect so we need to work together to remember the questions (and hopefully the answers). Thankfully, I remember the very first question (albeit not the actual wording of the question) but feel free to contribute your own and I'll stick it on the post.

Granted, I don't have much to contribute right now but I'm sure as people join in, we'll build up a right good answer list! :h:

Ribosomes are made up of what molecules? (1 mark)
Protein and rRNA

Describe how ribosomes are used to make polypeptides. Do not include transcription in your answer. (~3 marks)

Suggest how the student's scientific diagram could be improved (~2 marks)
Draw continuous lines
Do not use shading
Cohesive labelling

Compare and contrast how transmission electron microscopes and optical microscopes work, and their limitations and advantages (6 marks)
Optical microscopes work by firing light at the cell, whereas TEMs fire electrons.
TEMs are higher resolution - you can see small organelles, whereas in the optical microscopes you can only see large organelles eg the nucleus.
TEMs can go to 1,500,000x magnification, optical microscopes to 1,500x
/QUOTE]

TEMs fire a beam of electrons that travels through the specimen, while the specimen in optical microscopes reflect light
TEMs fire electrons in a vacuum so the sample must be dead, while optical microscopes can view living tissue Optical microscopes have a lower resolution because light has a longer wavelength: électrons travel faster so have a shorter wavelength, so TEM has high resolution Optical microscopes produce colour images while TEM produces black and white

Describe how ribosomes are used to make polypeptides. Do not include transcription in your answer. (~3 marks)

mRNA travels out of the nucleus onto the RER where it slots into the groove between the unit and subunit of a ribosome As ribosome translates the mRNA, complementary tRNA anticodons deposit amino acids that are joined by peptide bonds, creating a polypeptide chain

Also there was a question about, 'A scientists wanted to investigate a link between the size of seeds and air pollution of one species of tree. He was given a large sample of seeds from the city and a large sample of seeds from the countryside. Describe and explain how he would collect and process his results. (4marks)

Reply 10

I'm missing a couple questions, they might also be in the wrong order/mismatched but that's what I can remember.

Question 1
a) What two molecules are ribosomes made of? (1 Mark)
RNA and Protein
b) Describe the role of ribosomes in protein sythesis (do not write about translation. (3 Marks)
tRNA anticodon attachment, amino acid peptide bond forms, forms chain etc
c) DNA - mRNA base table (1 Mark)
d) Base code of mRNA and pre-mRNA is different, explain why. (2 Marks)
pre-mRNA has introns, mRNA goes through splicing so no introns

Question 2
a) Describe the structure of glycogen (2 marks)
a-glucose with 1-4/1-6 so heavily branched and compact due to helical shape (it does helical up)
b) Describe how glycogen is a good energy source in animals (2 marks)
readily hydrolysed the glycosidic bonds to give off energy and to produce ATP following aerobic respiration
c) What two adaptations does the cell membrane in the uterine lining have that makes it efficient for nutrient transport (2 marks)
many protein carriers, thin membrane (??)
d) Volume of each cell following 3 days of fertilisation (2 Marks)
Number/128

Question 3
a) Explain the action of the H+/Na+ Pump (3 Marks)
Both bind to seperate areas, ATP hydrolysis used to change protein shape to move Na+ against the gradient and then H+ moved out
b) Explain all the scientists results (Why mass increased and P value meaning) (4 Marks)
Mass increased because salt stayed high in gut so wp lowered, causign water to move in via osmis. P value of <0.05 meant that % due to chance was less than 5% so significant.
c) Increased salt results in tissue fluid build up, explain why. (2 Marks)
salt moves out b/c of hydrostatic but wp lower in tissue fluids, so cannot reenter. Lymphatic system cannot completely drain excess fluid

Question 4
a) Explain the 50 degree curve and the 60 degree curve (4 Marks)
60 was b/c of denaturation as it hit 0 pretty fast. 50 not sure, but fast reaction rate means substrate used up so less protease at max activity. Denaturation may have occured but not completely as curve leveled off not reach 0
b) Describe and explain the advantage of secreting extracellular proteins (2 marks)
c) Describe the action of membrane bound dipeptidases and explain the advantage (2 marks)
Hydrolyses the peptide bond between two amino acids in dipeptide, allows for absorbtion of amino acid.

Question 5
a) Describe how bacteria divide ( 2 Marks)
Binary Fission, organelles, plasmid and genetic material replicated and then grows and splits.
b) How much drug should be given to the mice? (2 Marks) 0.75g
c) Surface area/uncertainty maths questions (2 Marks) 19.85mm^3 iirc, 18.5%
d) explain how the bacterial resistance arised through natural selection and why two antibiotics should be used (3 marks) Usual natural selection answer, two should be used as liklihood of it being resistant to both is low so will wipe out bacteria.

Question 6
a) How does phagocytosis lead to antigen surface presentation (3 Marks)
Engulfment via endocytosis, lysosome fuses to vesicle, hydrolytic enzymes, debris contains antigens and is presented.
b) How does antigen surface presentation lead to antibody secretion (3 Marks)
T-helper cell binds to antigen, activates B cell, B cell divides into Plasma cells that secrete antibody specifc to antigen T-H cell bound to.
c) Why does the Viral protein lead to Rheumatoid Arthritis (2 Marks)
Similar shape to collogan so antibody will form a-a complex and mark collogan for destruction, RA is auto immune.

Question 7
a) Describe three variables that the scientist would have controlled (2 marks)
Light Intensity/Humidity/Soil Mineral Composition/Humidity/Temperature
b) Does the data support the conlcusion (4 Marks)
Yes, no lSD overlap. Shows that no effect on membrane for wheat but more ions leave for wild oats so membrane disrupted, loss of ions kills cells as no metabolic reagents.
c)

Question 8
a) Describe what Classification X and Y show in terms of evolutionary relationships (2 marks)
One was closely related where as the other had the same two species more distantly
b) Fill in the taxon table (1 Mark) D-O F was filled in
c) What Taxon were the scientists arguing over? (1 Mark) Genus
d) Describe three ways the scientists determien genetic relationships (3 Marks) Base Sequence, Amino Acid Sequence and Immunoglobin/Cytochrome C comparison

Question 9
a) Describe and explain 3 adaptations of tracheal systems for efficient gas exchange (3 Marks)
b) How does the gill in the larvae help it to be adapted to its behaviour (2 Marks) Counter current, max oxygen absorption for respiration as they actively hunt prey
c) Something here, not entirely sure tbh
d) Improve the scientific drawing (2 Marks) Continuous lines, no shading - straight line at base, labelling, magnification etc

Questions 10
a) Contrast principles and limitations of TEM and optical (6 Marks)
b) Explain the appearance of W and Z (both sex daughter cells, one had 4 cells, one had 2) (4 Marks)
c) Describe how the scientist should collect and process the data to see if there is a difference in seed size (5 Marks)

(edited 6 years ago)

Reply 11

LightAtTheEnd

12

The very last question was 5 marks.

Collection and Analysis of data:
Two groups of seeds, 1 from city trees and 1 from countryside trees.
Measure diameters of seeds for both groups
Find mean diameter of each group of seeds
Find SD for both groups.
Conduct statistical t-test to check for significance between two means.
Calculate degree of freedoms (n-1)
Compare value from t-test to critical value in the statistical table.
Will tell you if results are significant or not based on the comparison.

Potential marks:
Calculate volume of seeds (4/3 pi x r^3) so it's related to size?
Mention overlap of SD to also look at significance?

Reply 12

Amefish

OP

20

Original post by DrNippleson

I'm missing a couple questions, they might also be in the wrong order/mismatched but that's what I can remember.

Thanks for that! I'll get them put on.

Does anyone have any answers for the questions? Every answer is welcome!

Reply 13

Original post by Amefish

Thanks for that! I'll get them put on.

Does anyone have any answers for the questions? Every answer is welcome!

I'm adding the ones to mine now - should be up later

Reply 14

Luis99

Original post by DrNippleson

I'm missing a couple questions, they might also be in the wrong order/mismatched but that's what I can remember.

Question 1
a) What two molecules are ribosomes made of? (1 Mark)
b) Describe the role of ribosomes in protein sythesis (do not write about translation. (3 Marks)
c) DNA - mRNA base table (1 Mark)
d) Base code of mRNA and pre-mRNA is different, explain why. (2 Marks)

Question 2
a) Describe the structure of glycogen (2 marks)
b) Describe how glycogen is a good energy source in animals (2 marks)
c) What two adaptations does the cell membrane in the uterine lining have that makes it efficient for nutrient transport (2 marks)
d) Volume of each cell following 3 days of fertilisation (2 Marks)

Question 3
a) Explain the action of the H+/Na+ Pump (3 Marks)
b) Explain all the scientists results (Why mass increased and P value meaning) (4 Marks)
c) Increased salt results in tissue fluid build up, explain why. (2 Marks)

Question 4
a) Explain the 50 degree curve and the 60 degree curve (4 Marks)
b) Describe and explain the advantage of secreting extracellular proteins (2 marks)
c) Describe the action of membrane bound dipeptidases and explain the advantage (2 marks)

Question 5
a) Describe how bacteria divide ( 2 Marks)
b) How much drug should be given to the mice? (2 Marks)
c) Surface area/uncertainty maths questions (2 Marks)
d) explain how the bacterial resistance arised through natural selection and why two antibiotics should be used (3 marks)

Question 6
a) How does phagocytosis lead to antigen surface presentation (3 Marks)
b) How does antigen surface presentation lead to antibody secretion (3 Marks)
c) Why does the Viral protein lead to Rheumatoid Arthritis (2 Marks)

Question 7
a) Describe three variables that the scientist would have controlled (2 marks)
b) Does the data support the conlcusion (4 Marks)
c)

Question 8
a) Describe what Classification X and Y show in terms of evolutionary relationships (2 marks)
b) Fill in the taxon table (1 Mark)
c) What Taxon were the scientists arguing over? (1 Mark)
d) Describe three ways the scientists determien genetic relationships (3 Marks)

Question 9
a) Describe and explain 3 adaptations of tracheal systems for efficient gas exchange (3 Marks)
b) How does the gill in the larvae help it to be adapted to its behaviour (2 Marks)
c) Something here, not entirely sure tbh
d) Improve the scientific drawing (2 Marks)

Questions 10
a) Contrast principles and limitations of TEM and optical (6 Marks)
b) Explain the appearance of W and Z (both sex daughter cells, one had 4 cells, one had 2) (4 Marks)
c) Describe how the scientist should collect and process the data to see if there is a difference in seed size (5 Marks)

Wait so it actually is a pump?! I was just chatting a load of wham

Reply 15

Original post by Luis99

Wait so it actually is a pump?! I was just chatting a load of wham

It's an antiport, so it works in the same exact way as the Na+/k+ pump

Reply 16

Adam7789

Original post by DrNippleson

I'm missing a couple questions, they might also be in the wrong order/mismatched but that's what I can remember.

Question 1
a) What two molecules are ribosomes made of? (1 Mark)
b) Describe the role of ribosomes in protein sythesis (do not write about translation. (3 Marks)
c) DNA - mRNA base table (1 Mark)
d) Base code of mRNA and pre-mRNA is different, explain why. (2 Marks)

Question 2
a) Describe the structure of glycogen (2 marks)
b) Describe how glycogen is a good energy source in animals (2 marks)
c) What two adaptations does the cell membrane in the uterine lining have that makes it efficient for nutrient transport (2 marks)
d) Volume of each cell following 3 days of fertilisation (2 Marks)

Question 3
a) Explain the action of the H+/Na+ Pump (3 Marks)
b) Explain all the scientists results (Why mass increased and P value meaning) (4 Marks)
c) Increased salt results in tissue fluid build up, explain why. (2 Marks)

Question 4
a) Explain the 50 degree curve and the 60 degree curve (4 Marks)
b) Describe and explain the advantage of secreting extracellular proteins (2 marks)
c) Describe the action of membrane bound dipeptidases and explain the advantage (2 marks)

Question 5
a) Describe how bacteria divide ( 2 Marks)
b) How much drug should be given to the mice? (2 Marks)
c) Surface area/uncertainty maths questions (2 Marks)
d) explain how the bacterial resistance arised through natural selection and why two antibiotics should be used (3 marks)

Question 6
a) How does phagocytosis lead to antigen surface presentation (3 Marks)
b) How does antigen surface presentation lead to antibody secretion (3 Marks)
c) Why does the Viral protein lead to Rheumatoid Arthritis (2 Marks)

Question 7
a) Describe three variables that the scientist would have controlled (2 marks)
b) Does the data support the conlcusion (4 Marks)
c)

Question 8
a) Describe what Classification X and Y show in terms of evolutionary relationships (2 marks)
b) Fill in the taxon table (1 Mark)
c) What Taxon were the scientists arguing over? (1 Mark)
d) Describe three ways the scientists determien genetic relationships (3 Marks)

Question 9
a) Describe and explain 3 adaptations of tracheal systems for efficient gas exchange (3 Marks)
b) How does the gill in the larvae help it to be adapted to its behaviour (2 Marks)
c) Something here, not entirely sure tbh
d) Improve the scientific drawing (2 Marks)

Questions 10
a) Contrast principles and limitations of TEM and optical (6 Marks)
b) Explain the appearance of W and Z (both sex daughter cells, one had 4 cells, one had 2) (4 Marks)
c) Describe how the scientist should collect and process the data to see if there is a difference in seed size (5 Marks)

Great! 😀 But I think the surface area/uncertainty question was to do with the larvae, and in its place was a question on the antibiotic affecting mice and not human enzymes. There was also something for a log graph calculating the percentage difference

(edited 6 years ago)

Reply 17

seal9

9

Some of the q's/answers I can remember that I don't think have been answered here yet. They're in a random order and I'm not sure if all the answers are correct!

Describe the structure of glycogen (2 marks)
Contains alpha glucose, with 1,4 and 1,6 glycosidic bonds, and is also branched.

Describe why glycogen is a good energy source for babies (2 marks)
It's branched so is easily accessible in order for it to be hydrolysed for energy and converted into glucose. (Not too sure if that'd get you 2 marks - that's what I can remember)

Describe how bacteria divide (2 marks)
By binary fission, whereby the circular DNA and plasmids replicate (the plasmids sometimes replicate multiple times - DNA only once) and then divide into 2 cells.

How much of the antibiotic should be given to the mice per day? (2 marks)
0.75 mg.

Explain why the number bases in pre-mRNA and mRNA are different. (2 marks)
pre-mRNA contains introns, which are bases that do not code for amino acids. In mRNA these introns have been spliced out, so it only contains exons, decreasing the number of bases in it.

Two adaptations that make the uterus cell membrane efficient in transporting substances. (2 marks)
Thin cell membrane to allow a short diffusion pathway for substances, and a large surface area to increase the rate of diffusion.

Reply 18

Original post by Adam7789

Great! 😀 But I think the surface area/uncertainty question was to do with the larvae, and in its place was a question on the antibiotic affecting mice and not human enzymes. There was also something for a log graph calculating the percentage difference

haha, I did say they were mismatched rofl. My memory is only good to a point....

Reply 19

theforeigner