Paper 2 2026

explain how a resting potential is maintained inside the pacinian corpuscle /2

1.Membrane more permeable to potassium ions and less permeable to sodium ions;

2. Sodium ions actively transported / pumped out and potassium ions in.

describe how the pacinian corpuscle produces a generator potential when stimulated /3

• pressure applied deforms the lamellae

• lamellae and stretch-mediated Na+ ion channels deform and open, and Na+ ions flow in

• depolarisation

After the student had stared at a purple square, he saw a green afterimage.

suggest why /3

• red and blue cones stimulated

• red and blue stop working

• green still working

Cone cells give higher visual acuity than rod cells. Explain how/2

Each cone cell has separate bipolar neurone /separate ganglion cell

(So) no retinal convergence / impulses from each cone kept separate / no summation of impulses;

Exercise causes an increase in heart rate. Describe the role of receptors and of the nervous system in this process 4

Chemoreceptors detect rise in CO2 / H+ / acidity / carbonic acid / fall in pH

send impulses to cardiac centre / medulla;

More impulses to SAN;

By sympathetic

explain the role of chlorophyll in photolysis /3

• chlorophyll absorbs light and is oxidised

• releases excited electrons

• accepts electrons from water, eqm. shifts right

explain how the energy of light is converted into chemical energy in the light-dependent reaction /3

• chlorophyll is oxidised

• produces excited electrons that travel down electron transport chain

• energy released used to make ATP from ADP and Pi

explain why concentration of GP remains constant in a cell /3

• GP formed by RuBP + CO2

• GP → TP

• GP formed at same rate it is used

describe the light dependent reaction /6

• Light (energy) excites / raises energy level of electrons in chlorophyll;

• Electrons pass down electron transfer chain;

• Electrons reduce carriers

• Electron transfer chain associated with chloroplast
  membranes

• Energy released from chain used to ADP + Pi → ATP

• Photolysis of water produces O2, electrons and protons - some reduce chlorophyll

• NADP reduced by protons and electrons to NADPH

• NADPH and ATP enter light independent

suggest three ways to improve validity in a calorimeter experiment /3

• using water - high specific heat capacity

• leave air space - reduces heat gain

• use a stirrer - distributes heat evenly

most of the light falling on producers is not used in photosynthesis. suggest why /4

• does not hit chlorophyll

• CO2 conc. or temp. limiting factor

• wrong wavelength

• light reflected

describe how scientists could genetically engineer bacteria to produce a specific enzymes /6

1 Cut gene out of cell, obtain gene with restriction enzymes;

2       Cut DNA using restriction enzyme / plasmid cut with restriction enzyme;

3       Correct reference to sticky ends;

4       Join DNA using ligase / insert gene into vector;

5       Plasmid / named vector transferred to cell;

6       Method of transfer e.g. heat shock;

7       Reference to marker gene;

8       Select bacteria containing new gene

suggest why obtaining DNA fragments with a gene machine is faster than by converting mRNA to cDNA /1

faster gene machine waiting for all the enzyme-catalysed reactions

suggest why phosphorylation of a substrate will enable an enzyme-catalysed reaction to occur /1

substrate more reactive, lower Ea

explain what causes vision using the fovea to be in colour /1

there are three different types of cone cells sensitive to 3 different wavelengths

where are cone cells found and where are rod cells found?

cone cells at the fovea, no rods at fovea

peripheries of retina, only rods

Explain why it takes time for the rod cells to recover their sensitivity to light after moving into darkness /2

rhodopsin has been broken down

time to resynthesise

why might white light be difficult for rhodopsin to absorb?

contains a high proportion of wavelengths of light to which rhodopsin is not sensitive

explain why when an image is focused on the fovea, it is seen in colour /3

• colour is detected by cone cells

• large number of cones at fovea

• three different types of cones, each sensitive to light of a different wavelength

describe how cones allow for images to be seen in detail /3

• provides high visual acuity

• each cone cell connected to a separate neurone

• many separate impulses sent to the brain

explain how rods enable nocturnal organisms to hunt their prey /3

• retinal convergence/high sensitivity

• three rod cells connected to each neurone

• spatial summation allows threshold to be exceeded

give one similarity between taxis and tropisms /1

both are a directional response to a stimulus

Papaya plants reproduce sexually by means of seeds. Papaya plants grown from seeds are very variable in their yield. Explain why /2

meiosis/crossing over

random fertilisation

Explain how genetic fingerprinting allows scientists to identify the father of a particular panda cub /2

• all the bands in cub not from mother

• must be in father’s genetic fingerprint

explain why PCR was used for DNA fragments before gel electrophoresis /2

• only small amounts of DNA obtained

• ensures there is enough for genetic fingerprinting

explain why the DNA for each species of shark shows difference in base sequences /2

• variations in characteristics and features

• caused by mutations

explain why a primer will only bind to the DNA of one species /2

• primers bind by complementary base pairing

• primer has different DNA sequence to DNA of other species

the length of DNA fragment of each species in is different. explain why this is important in identifying the involved shark species /3

• fragments separated by gel electrophoresis

• different positions of bands can be identified on the gel plate

• shortest fragments move furthest

In conventional DNA fingerprinting, a series of bands is produced on the electrophoresis gel, resembling the rungs of a ladder. When the DNA in this new genetic fingerprinting technique is run in an electrophoresis gel it produces just one of these ‘rungs’.

Explain the reason for the difference in the number of ‘rungs’ produced/2

• traditional gel electrophoresis separates many lengths

• this method separates one lengths

Explain how DNA could be present on a toothbrush /2

cells present on toothbrush

all cells contain DNA

explain why it takes longer to obtain a genetic fingerprint if the sample is contaminated /1

other DNA must be removed

Explain how meiosis results in this plant producing gametes with these genotypes /2

meiosis separates homologous chromosomes

independent assortment

what is biomass

the mass of living tissue at a specific time in a given area

what is GPP

chemical energy store in plant biomass, in a given area or volume

what is NPP

the chemical store of energy in plant biomass in a given area or volume, after respiratory losses have been taken into account

why is the proteome larger than the genome?

post-translational modification of proteins

alternative splicing (different sections of DNA can be spliced, producing different proteins)

suggest why the scientists were unable to make a conclusion /3

no stats test

no data for egg

cannot compare to tadpole and adult

how does pyruvate enter the matrix in aerobic respiration?

active transport

what is pyruvate converted to in link, and how?

oxidised to acetate

how can lipids be used as a respiratory substrate?

lipids hydrolysed to glycerol and fatty acids

glycerol phosphorylated → triose phosphate, enters glycolysis then krebs

fatty acids → 2C fragment → acetyl coA, goes to krebs

how can proteins be used as a respiratory substrate?

proteins hydrolysed to amino acids, deaminated

3C compounds converted to pyruvate

4C and 5C converted to intermediates in krebs

Suggest the advantage of less blood flow in the mesenteric artery during exercise /3

more blood to respiring muscles

more oxygen available for aerobic respiration

meets increased demand for energy during exercise