Paper 3 Unofficial Mark scheme

Question a,b,c,d

Question:

/ Mark

[mark scheme]

Discussion

1a

What is colonisation habitat?

/1

• colonise is when a species is introduced into a habitat and grows in a habitat
• Dominant among other species

• colonise is when a species is introduced into a habitat and grows in a habitat
• I also added they become the dominant species, would i have lost the mark ?
• Should there be something about pioneer species

1b

IAA phototropic affect  ison plant shoot growth isn’t

/3

IAA is produced in shoot tips.

It diffuses to the side of the growing shoot tip with a lower light intensity.

Where it causes elongation of cells. u get a mark for explaining how so e.g lowering ph of cell walls

So the shoot tip grows towards the light. positive phototropism

 I didn't say diffuse, I just said moves is diffuse a key word, I'm gonna cryyyyy

My teacher said meristem is where its produced do you think that would count?

1c

Graph on plant shoots and routes and IAA

/2

2:

Where does light dependant reaction takes place

/it 1

Thylakoid membrane only

Role of Rubisco in the light-dependent reaction?

/4

RUBISCO is an enzyme (description)

RUBISCO fixates Carbon from Carbon Dioxide into GP.

So its role is to fix Carbon from the atmosphere into plant biomass.

This felt similar to a paper 1 question, idk if it’s just me?

No it was similar I think ah okay

Samee

YES I WROTE THIS EXACT ANSWER ON PAPER ONE I WAS SO CONFUSED

Role of chlorophyll

• /2

Chlorophyll is a photosynthetic pig ment containing photosystems.

Photosystems allow for transfer of energy from photons to excite electrons and to photolyse water.

Electrons are released into the electron transport chain

Hydrogen ions from water needed for chemiosmosis to produce ATP.

How does an Oxygen probe indicate how Temperature Of water  impacts GPP?

wasn't this a practical question?

/4

Levels of oxygen in water increase as rate of photosynthesis increases (photolysis releases oxygen)

Rate of photosynthesis affected by temp, the higher the temp the higher the rate (Coz enzyme activity of ATP synthesesg increases)

As photosynthesis increases biomass in aquatic plants increases (more energy stored as GALP)

So overall an inc in o2 means higher temp and higher rate of photosyth and higher GPP

It was a microorganism not a plant - i dont think it was - plankton oh your right ffs i just checked

Wait is it a plant or micro organism lol - this is confusing me it was a micro organism but it does photosynthesise i fucked it up

Oh fuck i did it wrong

They photosynthesis

Yeah they basically are plants

They’re protoctists but can photosynthesise

R u fuckinb serious

I swear it was plant 🙏😫

Oh thank god

This q took too much of my brain power, if its wrong I'm quitting

Describe the relationship between Gross Primary Product and Net Primary Product

/2

Net Primary Product is Gross Primary Product minus the energy used during respiration.

How to safely place discs on bacterial lawn safely

/3

Using tweezers/other named appropriate tool

Sterilisation by disinfectant and heating under flame.

Work near a bunsen burner to cause updraught.

aseptic techniques

Antiseptic technique

Flame forceps

Open lid of petri dish marginally? As small as possible?

Antiseptic wipes to clean surface of working environment

Work near open bunsen burner flame

Wash hands w soap?

3?

A graph on an inhibitor protease and a normal  protease and why a homozygous tmi1 was used

/2

Homozygous Tmi1 was used, as a mutation could otherwise cause the other allele to be expressed (if heterozygous)

And this would) invalidate the results of the investigation.

3b?

Tmi1 mutant vs norm  I al mutant?

/2

The mutation led to a different primary structure of the protein receptors for IAA.

So the tertiary structure/3D shape of the receptors were no longer specific to IAA

So IAA could no longer bind to mutants/the mutant receptors were desensitised

So less growth occurs.

Thats rlly smart ngl

It still produces latera

Thats why i said LESS

Calculation question on the zone of inhibition

/2

19 and 284 / ECF

How to see if result is anomalous

/2

Repeat the investigation multiple times

To see if there are anomalous data points in the original investigation

Why is the concentration of the enzymes and substrates important for the initial rate of reaction in this investigation?

/3

A higher enzyme/substrate concentration in the same volume means more collisions per unit time.

So there are more frequent enzyme-substrate complexes formed.

So for this investigation, these had to be kept constant to make the investigation valid.

Idea of control variables and experimental design.

I waffled so hard, but I said smth like the higher the enzyme substrate conc is the more particles so the more chance of freq Collisions/ successful collisions in shorter time, so more enzyme substrate complexes form? I said the samr thing it should be right

5?

 Explain why an area of ocean can support more biomass of a humpback whale and not a white shark

/3

Energy transfer efficiency decreases with each trophic level.

Humpback whales feed on primary consumers (krill), leading to less energy loss,

Compared to white sharks that feed on secondary consumers.

So more biomass from primary consumers can be stored as biomass in humpback than in sharks.

Idea of energy transfer in trophic levels.

I spoke about trophic levels?

What did u say ? Coz I didn't really get this q I waffled

I wrote about more trophic levels means more energy lost to respiration excretion etc  -

i said one of the whales was a secondary consumer and one was tertiary consumer and more  trophic levels= more energy lost ??????waffle

I also said that it’s a secondary tertiary consumer

oh no i just said there’s bare krill

Is biomass about size tho cause plants have more biomass than us don’t they? I put about trophic levels

3

Role of gp120

/2

Has a complementary shape to CD4 receptors

So it can fuse with the cell surface membrane of the host cell and insert viral RNA

By binding to specific/complementary receptors.

I said binds to cd4 receptors ?

Oh sugar, i should have said that

I said its undetected by the immune response cells?

I said that it takes the cell surface membrane as its envelope when it buds from the cell?

Why does HIV have the host cell proteins on it?

2

Because virions are assembled at the host cell membrane.

When HIV infects hosts cells they become antigen presenting (due to fusion of phospholipid bilayers)

This is part of budding - the natural process by which the virion is produced when exiting host cells. (extra context for u)

Using protease? To break a chain into proteins

/3

HIV protease is an enzyme.

The enzyme must have a specific active site specific to the amino acids at the end of each individual protein.

So it can form a specific enzyme-substrate complex at that point.

And catalyse the breaking of peptide bonds (between amino acids) by hydrolysis.

I said it isolates the protein by binding to the binding areas and hydrolyzes the peptide bonds which breaks the polypeptide into proteins

I also said smth like that

Could you write about short tandem repeats? Um Wtf is that

6

MDMA effect the rate of transmission?!

/3

MDMA is a serotonin reuptake inhibitor.

Prevents reuptake of serotonin into presynaptic neurons.

So the concentration of neurotransmitter serotonin remains high at the synapse.

So neurotransmitter serotonin binds to (ligand-gated sodium ion channels/)specific receptors at the postsynaptic membrane more often 

Because a higher concentration means more collisions per unit time.

So there are more frequent action potentials induced.

Mice experiment with MDMA buttons and control buttons

Ratio question

Comment on the graph

/3

/2

MDMA increased number of buttons as mice received relief, and feelings of happiness (as causes increase in serotonin)

After a while (8/9 days) mice had become habituated to this stimulus, effects weren’t as readily available. Mice decide there is no benefit of the button so do not press.

GUYS HOW DO

7a

The dreaded 9 marker.

myelin sheath and conduction graphs about different cold treatments and which reduced pain from latic acid

/9

Ice massage and ice pack

Idea that ice melted by surface temperature.

Idea that ice had a lower impact because of the high specific heat capacity of water in blood plasma/tissue meaning that changing core temperature needs a lot of energy.

Idea that lower impact of ice is because it is close to the dermis - link to the fact that there were great changes in sensory neurons (close to skin) but not motor neurons.

Cold water immersion

Idea of higher temperature gradient.

Increase in impulse latency in motor neurone was higher than others and decrease in amplitude and velocity was lowest of all treatments

Kinetics

Link to lower temperature meaning less collisions of neurotransmitters at the synapse.

Idea of temperature’s impact to subsequent lower amplitude due to fewer neurotransmitters binding to (ligand-gated sodium ion channels/)specific receptors on the postsynaptic membrane, so less likely to surpass threshold potential.

Lower frequency of impulses as a result means less pain perception as intensity of feeling is dependent on frequency of synaptic transmission (for context - the amplitude of a single action potential is constant, it is frequency which determines our perception of intensity)

Conclusions

All of the treatments could lead to relief - but we don’t have any qualitative analysis of whether the changes in amplitude led to any change in physical feeling.

There is no indication of the long-term impact on pain and whether or not relief continues after the treatment course.

Worth noting that the investigation should be repeated independently to produce a valid set of results and should be peer-reviewed.

Idea that statistical tests can only take place when multiple repeats have been carried out.

Idea that statistical t-tests should be used to establish whether there is a significant effect arising from the treatment.

Gradient in micrometres at 7? yes

/2

2.8 + the unit which i forgot

Method: calculate y = mx + c

/equation for gradient

Insert x = 7.

I got 2.8 n         n                       nm

a

phylogenetic tree with amino acids from eye lens a nd

/3   bb

Molecular phylogeny (/proteomics) can be used. In

Compare the amino acids sequence of the proteins present in the eye lens proteins.

The more differences in the amino acids sequence of the proteins the more distant their last common ancestor.

This can be drawn in a phylogenetic tree to understand how the eye lens protein has evolved.

period.

how can a Spirometer be used to find the metabolic rate

/4

Keep room temperature the same? measure oxygen/spirometer vol before and after period

GUYS ITS SPIROMETER NOT RESPIROMETER??u lot are all on abt respirometers how else are you gonna measure metabolic rate this is continuous flow meter i think

I said like use the spirometer trace to find o2 consumption per min using difference between two adj peaks could be wrong tho

Yh i said that asw

Should be increased minute ventilation needs increased energy in order to actually. Oxygen released is a by-product of ventilation. More oxygen, more ventilation-  ventilation requires ATP and energy, indicating higher metabolic rate of an organism.

Soda lime to absorb CO2

I said Put The Spirometer on the sloth, how does that work am I cooked? LOL

if you've seen the past paper question about some animal in the spirometer box it's like that… measure oxygen consumption and divide by body mass of the sloth control temperature and body mass

I said tie the spirmoter to the sloths mouth IM ABSOLUTLEY COOKED (at least it made me smile in the exam instead of cry)

This is making me giggle

Same

This question was about phytoplankton NOT about the sloths. Soda lime was not necessary as phytoplankton are photosynthetic organisms, and use CO2.

Um nah mate this was for the sloth. Oxygen probe was phytoplankton

Oh im so confused lmaooo but there was this exact question abt metabolic rate

Why is the ‘lattice of tendons of digits which draws to a close when at rest’ beneficial?

/3

Because sloths have an arboreal lifestyle (they spend most of their life hanging upside down.

It means they don’t have to waste energy when hanging upside down as their claws are drawn to a closed position at rest.

So they can resist predation from eagles (as given in the article) and their arboreal lifestyle doesn’t take up a lot of energy.