Zzbc
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Unofficial mark scheme for OCR Biology A level paper 1 2018

Please add your answers

So far the mark scheme is looking like this- do not have all the questions especially multiple choice and also this markscheme is not 100% accurate or correct. Obviously will have mistakes, I have tried to compile the answers that have come up the most frequently and obviously in the real mark scheme they will have their marking points that may or may not be included in here. I’m sure there are many points that have been missed so please feel free to add! But hopefully this compiles everything for everyone:

Multiple choice:

Gaseous exchange- thin surface lining
%change between respiration in men- 12.3%
Molecule- debate between nucleotide and carbohydrate
Area of brain for instrument- W and Z
Neurones- spatial summation
DNA replication- length remains same between the strands (debatable some for complementary pairing)
Iodine- kidney more efficient at removing iodine than lungs
Medical use for sympathetic synapse blocker- only for tachycardia and blood pressure
Graph to show effect of inhibitor- Second line from the top (B)
Sensory neurone- cell body outside of axon




Question 1

A) Type 2 diabetes. insulin is being produced however not affecting body cells. In type 1 little/no insulin is produced. (2 marks)

ii) exercise and careful control of diet (2marks)

B) debatable Liver tissue seems to be most popular but cardiac and adipose possible (1 mark)

ii) glucose is a respiratory substrate and can produce atp which is required to unbind the globular myosin heads from the actin-myosin cross-bridges so it can re-bind along the filament and contract again. Something along those lines (3 marks)

C) student is wrong: % decrease in oxygen uptake is above 20% (people got between 35-45% ish) data is not representative enough to validate the hypothesis as only one pregnant woman is used and does not show effect across whole of pregnancy (3 marks)

2a) photosynthetic pigments absorb different wavelengths of light and reflect what they don’t absorb
- in photosynthesis accessory pigments absorb and reflect light in the photosystem
- the pigment chlorophyll a in the primary pigment reaction center of the photosystem absorbs light which excites the electrons in the magnesium passing them along the electron transport chain (4marks)

Why they have pigment C-

Organism lives in water and therefore receives different wavelengths of light. Would absorb different wave lengths of blue/green light than normal organisms hence the need for different pigments in order to maximise absobtion of light (1 mark)

Differences:

Contains only 3 thylakoids stacked whereas normal has many thylakoids stacked called grana
Contained no integranal llamellae whereas normal do
Possible normal has starch grains other didn’t (2 marks)

Respiratory quotidiens: carbohydrate, protein, lipid respiratory quotients: carbohydrates-1, protein-0.9, lipids-0.7
3. differences and similarities in glycogen and chitin
Both have a six membered ring
Both have 1,4 glycosidic bonds

Differences- glycogen forms both 1,4 and 1,6 glycosidic bonds. Chitin just 1,4 glycosidic bonds
Glycogen is branched chitin is straight chaIned
Glycogen contains alpha glucose monomers, chitin contains n-acetylglucosamine monomers or different group on 2nd carbon
(4 marks)
Adaptations of cellulose
-strong
-fibrous
-water insoluble
-tasteless?
(3 marks)

Chemiosmosis (6 marker)
NADH transports H+ ions and electrons to inner mitochondrial membrane. oxidised and reduces along the electron transport chain. Protons pumped across memebrane , a concentration gradient builds , electrons go through complexes, supplied by NAD and FAD, Through ATP synthase and producing ATP from ADP and Pi NADH transports H+ ions to inner mitochondrial membrane. How it is oxidised and reduces along the electron transport chain. Oxygen is the final electron acceptor. Something along those lines

area A shows the phospholipid bilayer hydrophilic head and hydrophobic tail forms the phospholipid which creates the bilayer partially. Some debate on mention of cholesterol however was specific to diagram so may not be allowed (2 marks)

Role: membrane used to separate contents of organelles - compartmentalisation
Membrane used to form vesicles for enzymes etc
Increases surface area in mitochondria etc

Potometer question: wanted to compare transpiration in 2 different species of plant

Keep temperature, light intensity and wind speed the same.
Ensure both plants species healthy
Set up potometer
Allow plants 2 minutes to adjust
Record initial position of bubble
After certain length of time record new position of bubble
Distant moved by bubble/ time taken = rate of transpiration
Repeat and get average result (6 marks)

Beetroot experiment

1. Assumption pigment release depends on permeability of membrane - place in diff concentrations of ethanol
2. Assumption pigment released when cut- wash beetroot
3. Assumption absorption related to pigment released- use colorimeter (3 marks)

Keep controlled-
size of beetroot tubules
Beetroot plant used
Dry each beetroot pieces after washing
Same Colorimeter/ calibration used
(2 marks)

Criticisms of graph:
No units given for concentration of ethanol
Presented in bar graph
No line of best fit (3 marks)

Average can be used to give more accurate representative results and remove any anomalies ( 2 marks)

3 tissues: (some debate)
1. liver
2. Pancreatic
3. Muscle
(3 marks)

Effect of neurotoxin on nerve impulses:
Accs as non competitive inhibitor by changing tertiary structure of sodium ion channels
Sodium ions can no longer enter the axon and depolarise it to the threshold value of -70mv
Action potential can no longer be propagated
Axon remains at resting potential
Neurones will not transmit impulses & stimuli not responded to (4 marks)

Effect on heart rate
cause atrial fibrillation
SAN would still be sending signal to AVN so atrial systole would continue
However as the AVN to apex of the heart via purkyne fibres would be slower ventricular systole would be delayed
This would mean atrial systole would be occurring more frequently than ventricular systole causing an irregular heart beat (3 marks)

Respirometer questions

Calculating rate of respiration at 0 ( in dark)
pi r^2 x height = volume
Pi x 0.05^2 x 3.7 = 0.029045 mm3 in 3 hours
0.02904/3 = 0.00968mm3 per hour (3 marks)

Percentage change = +142-143% roughly (2marks)

soda lime was not used as seedlings were photosynthesising and therefore would need to take up the CO2.

Explanation: at 1500lux = 0 so rate of photosynthesis = rate of respiration
After 1500 +ve value for liquid moved so rate of photosynthesis > respiration as more O2 produced

Mistakes:
-CO2 or haemglobonic acid
-Accelerator nerve not vagus
-Adrenaline binds to the SAN not AVN
-cardiac muscle not smooth
-Chemoreceptors not Baroreceptors detect the change in pH of blood
(4 marks)

Baby reflex-
action of putting their arms out and back in rapidly would thrust the head forwards counteracting the lack of head support
Crying signifies to carer that baby is in distress so that carer can support the babies head
Response is rapid as reflex hence reducing risk of harm to babies neck. moro reflex is to grab hold of something to prevent falling (2 marks)


receptors in eye detect movement close to eye as stimuli
Sends impulse through sensory neurone to relay neurone and bypasses the brain
Impulse travels down motor neurone to effectors causing the eyelid to shut as an involuntary reflex response. It’s a cranial reflex it is not communicated down the spinal cord which gives a much faster response to a given stimulus. I guess you could mention the frequency of action potentials for a given stimulus (3 marks
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Zzbc
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Question 1

Type 2 diabetes as although insulin was being produced was having no effect on body cells hence the high levels of glucose

Exercise and careful control of diet for treatments

Put adipose (fat) tissue but unsure

Can’t remember the last part

For the graph of spirometer

Said student was wrong as uptake of oxygen was 37% less than normal women. Also she only compared the data for one pregnant woman so it is not representative enough to give a valid hypothesis
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James-peck
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I got for multiple choice:
1.a
2.b
3.b
4.c
5.b
6.d
7.a
8.a
9.c
10.c
11.d
12.c
13.d
14.d
15.c

Probs not right tho
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medwannabee
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(Original post by James-peck)
I got for multiple choice:
1.a
2.b
3.b
4.c
5.b
6.d
7.a
8.a
9.c
10.c
11.d
12.c
13.d
14.d
15.c

Probs not right tho
Do you remember the actual answers?
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Zzbc
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Question on photosynthetic pigments

- photosynthetic pigments absorb different wavelengths of light and reflect what they don’t absorb
- in photosynthesis accessory pigments absorb and reflect light in the photosystem
- the pigment chlorophyll a in the primary pigment reaction center of the photosystem absorbs light which excites the electrons in the magnesium passing them along the electron transport chain

Why they have pigment C-

Organism lives in water and therefore receives different wavelengths of light. Would absorb different wave lengths of blue/green light than normal organisms hence the need for different pigments in order to maximise absobtion of light

Differences:

Contains only 3 thylakoids stacked whereas normal has many thylakoids stacked called grana
Contained no integranal llamellae whereas normal do
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medwannabee
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What was the answer for the percentage change from the 20 year old to the 45 year old? Got stuck
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Zzbc
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(Original post by medwannabee)
What was the answer for the percentage change from the 20 year old to the 45 year old? Got stuck
12% I think
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florence_
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(Original post by Zzbc)
12% I think
Yh I got 12.3%
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abigailsnail
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For chemiosmosis 6 marker - just talked about H+ gradient and changing shape of ATP synthase enzyme to synthesis ATP from ADP and pi? what else could you mention?
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medwannabee
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(Original post by florence_)
Yh I got 12.3%
(Original post by Zzbc)
12% I think
Thanks you!!! Phewwww
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florence_
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For the ant question with RQ values, what did you put for the middle one?

Because I got 0.9 (which is protein), but that's usually only used if there isn't any thing else.
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RevisionGuide
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Anyone else put use of Metformin as a treatment for gestational diabetes?
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Zzbc
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Think for multiple choice

For gaseous exchange- thin surface lining
For rate on transpiration- occurs on surface of leaf
For molecule- got nucleotide but not confident in that
Area of brain for instrument - W and Z
For neurones- spatial summation
For rate of respiration in men- 12% ish
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Zzbc
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(Original post by abigailsnail)
For chemiosmosis 6 marker - just talked about H+ gradient and changing shape of ATP synthase enzyme to synthesis ATP from ADP and pi? what else could you mention?
How NADH transports H+ ions to inner mitochondrial membrane. How it is oxidised and reduces along the electron transport chain. Oxygen is the final electron acceptor?
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abigailsnail
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Transpiration 6 marker - just talked about what factors needed to be controlled and use of repeats to make it valid
For the ants what food they ate i put 'protein' then 'lipid and carbohydrate' - did you have to quote specific respiratory quotients?
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Rj2018
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(Original post by Zzbc)
Question 1

Type 2 diabetes as although insulin was being produced was having no effect on body cells hence the high levels of glucose

Exercise and careful control of diet for treatments

Put adipose (fat) tissue but unsure

Can’t remember the last part

For the graph of spirometer

Said student was wrong as uptake of oxygen was 37% less than normal women. Also she only compared the data for one pregnant woman so it is not representative enough to give a valid hypothesis
I thought it was 45% less?
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huntforalice
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For the spirometer Q and pregnant lady did anyone else get a reduction of 35% or near? Or was that just me messing up lol
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abigailsnail
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thanks so much! Hopefully i still got about half marks on that

(Original post by Zzbc)
How NADH transports H+ ions to inner mitochondrial membrane. How it is oxidised and reduces along the electron transport chain. Oxygen is the final electron acceptor?
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abigailsnail
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What was the answer for the question about slowing the conduction in purkyne fibres? I said about slowing systole but i don't think thats right
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georgelagalle
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(Original post by abigailsnail)
For chemiosmosis 6 marker - just talked about H+ gradient and changing shape of ATP synthase enzyme to synthesis ATP from ADP and pi? what else could you mention?
You basically had to outline all of oxidative phosphorylation
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