Unit 1 - 4 - Hard

Question 1

Cyclin D stimulates the phosphorylation of DNA polymerase, which activates the DNA polymerase. Describe how an enzyme can be phosphorylated.

Answer 1

1. Attachment/association of (inorganic) phosphate (to the enzyme)
2. (Released from) hydrolysis of ATP

Question 2

It can be 6-12 months before HPV antibodies can be detected in the blood of individual with a HPV infection. Use Figure 1 to suggest why this is.

Answer 2

It takes 6-12 months for antibodies to be detected in a HPV infection because:

Few virus proteins are expressed in the lower layers of the epidermis, so infected cells do not become antigen-presenting cells: [1 mark]

Viral proteins/antigen-presenting cells produced at the skin surface are quickly lost/shed from the body, so are not detected by the cells of the immune system; [1 mark]

Without antigen-presenting cells, T cells / B cells are not activated; [1 mark]

[Total: 3 marks]

Question 3

Figure 2shows the SGLT1 polypeptide with NH2at one end and COOH at the other end.Describe how amino acids join to form a polypeptide so there is always NH2at one end and COOH at the other end.

Answer 3

1. One amine/NH2group joins to a carboxyl/COOH group to form a peptidebond;

Accept on diagram, for example (at least) two amino acids joining by a correctly drawn peptide bond (MP1) with NH2at one end and COOH at the other (MP2).Ignore incorrect names of NH2and COOH groups.

2. (So in chain) there is a free amine/NH2group at one end anda free carboxyl/COOH group at the otherOREach amino acid is orientated in the same direction in the chain;

Question 4

Oedema is a condition characterised by an abdomen and limbs that are swollen with fluid. It is prevalent in poorly developed areas in the African continent due to the low protein diet of the people living there. Explain how a low protein diet could result in oedema.

Answer 4

A low protein diet could result in oedema because:

• Low protein levels result in fewer plasma proteins in the blood; [1 mark]

This means that the water potential of the plasma is increased / too high / not low enough (at venule end of capillary); [1 mark]

Water is not reabsorbed / less water is reabsorbed by osmosis into capillaries/blood;

[1 mark]

• Tissue fluid collects/builds up in the tissues in the abdomen and limbs; [1 mark]

Question 5

Explain the difference in the structure of the starch molecule and the cellulose molecule shown in the diagram above.

Answer 5

Starch formed from α-glucose but cellulose formed from β-glucose;

2. Position of hydrogen and hydroxyl groups on carbon atom 1 inverted;

Question 6

State two functions of membranes in living cells.

Answer 6

Any two of the following:

Separate the internal cell environment from the external environment; [1 mark]

• Separate the internal cellular compartments/organelles; [1 mark]
• Enable cellular conditions to be different between one enclosed space and another;

[1 mark]

Regulate the movement/exchange of substances; [1 mark]

An interface for communication / displaying antigens / displaying receptors; [1 mark]

Question 7

Describe the roles of iron ions, sodium ions, and phosphate ions in cells.

Answer 7

Iron ions

1. Haemoglobin binds/associates with oxygen

OR

Haemoglobin transports/loads oxygen;

Ignore reference to 2+ or 3+ in Fe2+ or Fe3+

Sodium ions

2. Co-transport of glucose/amino acids (into cells);
3. (Because) sodium moved out by active transport/Na – K pump;
4. Creates a sodium concentration/diffusion gradient;
5. Affects osmosis/water potential;

Phosphate ions

6. Affects osmosis/water potential;

Accept 5. OR 6. – not both

7. Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides;
8. Used in/to produce ATP;

Reject ‘energy produced’

9. Phosphorylates other compounds (usually) making them more reactive;
10. Hydrophilic/water soluble part of phospholipid bilayer/membrane;

Question 8

Draw an antibody

Answer 8

Question 9

Particulate matter is solid particles and liquid particles suspended in the air. Polluted air contains more particulate matter than clean air. A high concentration of particulate matter results in the death of some alveolar epithelium cells. If alveolar epithelium cells die inside the human body they are replaced by non-specialised, thickened tissue. Explain why the death of alveolar epithelium cells reduces gas exchange in human lungs.

Answer 9

1. Reduced surface area;
2. Increased distance for diffusion; Accept description of efficient gas exchange in the healthy alveolar epithelium as long as a reference is made to the damaged tissue changing this.
3. Reduced rate of gas exchange;

Question 10

Figure 1 below shows a cell surface membrane and some molecules of a small, nonpolar substance known as substance X.

Answer 10

Substance X will…

Move from the outside of the cell to the inside; [1 mark]

Directly through the cell (surface) membrane / in between the phospholipids / by simple diffusion; [1 mark]

Because…

There is a higher concentration of substance X outside the cell than inside / diffusion takes place down a concentration gradient; [1 mark]

The molecules are small and nonpolar so can move between the (tails of the) phospholipids; [1 mark]

[Total: 4 marks]

Question 11

Hydrostatic pressure = 4.3 kPa Hydrostatic pressure = 1.6 kPa

Tissue fluid

Hydrostatic pressure = 1.1 kPa

(a) Use the information in the figure above to explain how tissue fluid is formed

Answer 11

1.

(a) 1. (Overall) outward pressure of 3.2 kPa;
2. Forces small molecules out of capillary.

Question 12

Scientists have found that transcription of the LAT gene produces a microRNA.
This microRNA binds to some of the nerve cell’s own mRNA molecules. These mRNA molecules are involved in programmed cell death of nerve cells. The scientists concluded that production of this microRNA allows HSV to remain in the body for years

(d) The scientists concluded that production of this microRNA allows HSV to remain in the body for years (lines 10–12).
Explain how this microRNA allows HSV to remain in the body for years.

Answer 12

(d) MicroRNA binds to cell’s mRNA (no mark)
1. (Binds) by specific base pairing;
2. (So) prevents mRNA being read by ribosomes; 3. (So) prevents translation / production of proteins;
4. (Proteins) that cause cell death.

Question 13

c) Genetics and nutrition are two factors that influence blood pressure in humans. Explain how very high blood pressure may affect an individual’s circulatory and lymphatic system.

Answer 13

High blood pressure may result in the following effects on an individual’s circulatory system:

Increased blood pressure could damage blood vessels OR valves; [1 mark]

Increased chance of heart attack OR stroke; [1 mark]

Increased outward pressure of blood at the arterial end of capillaries; [1 mark]

Higher volume of tissue fluid forms / not all tissue fluid is reabsorbed/drains; [1 mark]

This leads to swollen limbs (due to accumulation of tissue fluid); [1 mark]

Question 14

Mitochondrial disease (MD) often causes muscle weakness (lines 1–3). Use your knowledge of respiration and muscle contraction to suggest explanations for this effect of MD.

Answer 14

a) 1. Reduction in ATP production by aerobic respiration;
2. Less force generated because fewer actin and myosin interactions in muscle;
3. Fatigue caused by lactate from anaerobic respiration.

Question 15

Describe the role of spindle fibres, mitosis

Answer 15

1. C-prophase and

D= metaphase and

E = anaphase,

2. (In) prophase, chromosomes condense
3. (In) prophase OR metaphase, centromeres attach to spindle fibres,
4. (In) metaphase, chromosomes/pairs of chromatids at equator/centre of spindle/cell

5 (In) anaphase, centromeres divide,

6 (In) anaphase, chromatids (from each par) pulled to (opposite) polesiends (of cell 7) prophase/metaphase anaphase, spindie

fibres shorten

Question 16

(b) Give two assumptions made when using the mark-release-recapture method.

Answer 16

1. No emigration / immigration;
2. No losses to predation;
3. Marking does not affect survival;
4. Birth rate and death rate equal;
5. (In this case) all belong to one population.

Question 17

Describe the role of micelles in the absorption of fats into the cells lining the ileum

Answer 17

1. Micelles include bile salts and fatty acids; Ignore other correct components of micelles.
2. Make the fatty acids (more) soluble in water; For ‘fatty acids’ accept fats / lipids.
3. Bring/release/carry fatty acids to cell/lining (of the ileum); For ‘fatty acids’ accept fats/lipids.
4. Maintain high(er) concentration of fatty acids to cell/lining (of the ileum);
5. fatty acids (absorbed) by diffusion;

Question 18

Give oneadvantage of viewing a biological specimen using a transmission electron microscope compared with using a scanning electron microscope.

Answer 18

Higher resolution OR View internal structures;

Question 19

Speciation is far less frequent in the reformed Amazonian forest. Suggest one reason for this.

Answer 19

Similar / same environmental / abiotic / biotic factors / similar / same selection pressures / no isolation / gene flow can occur (within a species);

Question 20

What two measurements are needed to calculate an index of diversity?

Answer 20

1. Number of (individuals of) each species;
   Accept: ‘population’ for ‘number’
2. Total number of individuals / number of species

Question 21

The manufacturer concluded that enzyme B would be the best enzyme to use. Use the results from Figure 2 to evaluate this conclusion.

Answer 21

Any three of the following:

• Enzyme B is more effective across a range of temperatures / at lower and higher

temperatures: [1 mark]

• Enzyme B denatures at 80°C and enzyme A denatures at 60°C; [1 mark]

⚫ However, enzyme A has a higher maximum rate of reaction: [1 mark]

• Only 2 enzymes were investigated; [1 mark]

Question 22

The blood plasma in Figure 1 has a more negative water potential at the venule end of the capillary compared to the arteriole end of the capillary. Explain why.

Answer 22

Any three of the following:

Water has diffused out via osmosis OR left the capillary; [1 mark]

Proteins in the blood are too large to leave/pass through wall of the capillary; [1 mark]

This means there is a higher/ increased concentration of blood proteins at venule end;

[1 mark]

• Higher concentration of blood proteins results in lower water potential; [1 mark]

Question 23

Describe the structure of DNA

Answer 23

1. Polymer of nucleotides;
2. Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base;
3. Phosphodiester bonds (between nucleotides);
4. Double helix/2 strands held by hydrogen bonds;
5. (Hydrogen bonds/paining) between adenine, thymine and cytosine, guanine

Question 24

(d) Calculate the number of insects on this island 1 day after release of the marked insects.
Show your working.

Answer 24

(d) 10 130. Tolerance of ±1

Question 25

An athlete has discovered that he is anaemic. A person suffering from anaemia has a decreased concentration of haemoglobin in their blood. Suggest and explain how being anaemic may affect the athlete’s performance.

Answer 25

It will negatively affect their performance OR it will decrease their ability to perform OR

they will be slower: [1 mark]

Anaemia will have this effect on performance because: two of the following:

Decreased haemoglobin means less oxygen is delivered to active muscles OR fewer haemoglobin molecules means there are fewer oxygen molecules available; [1 mark]

(Less oxygen leads to) reduced aerobic respiration; [1 mark]

(Reduced aerobic respiration means) less energy/ATP available for muscle contraction

OR reduced muscle contraction; [1 mark]

Question 26

Figure 1 shows a molecule (X) that is about to be transported across a cell membrane.

Figure 1

Low concentration

Exterior

High concentration

Cytoplasm

Describe the events that would take place in order for molecule X in Figure 1 to move from the exterior of the cell into the cytoplasm.

Answer 26

Molecule X binds to a specific binding site on the carrier protein; [1 mark]

ATP is hydrolysed / broken down to release energy; [1 mark]

The protein changes shape AND releases/transfers/transports/moves molecule X into the cytoplasm; [1 mark]

Question 27

The data in Table 7 show differences between the oxyhaemoglobin dissociation curve

for a mouse and the oxyhaemoglobin dissociation curve for a horse.

Suggest how these differences allow the mouse to have a higher metabolic rate than the horse.

Answer 27

Mouse

1. (Smaller sở) larger surface area to volume ratio;
2. More/faster heat loss (per gram/in relation to body size);
3. (Faster rate of) respiration/metabolism releases heat;

Question 28

In Figure 1. between 90 and 120 mins the rate of transpiration begins to slow in the leaves for both sets. Explain why this happens.

Answer 28

rate of transpiration between 90 and 120 minutes begins to slow because:

Water is being lost by transpiration/evaporation from the stomata; [1 mark]

Water is not being replaced OR there is no water supply; [1 mark]

Water loss causes the stomata to close OR the water potential gradient between the leaf and the air has reduced/decreased; [1 mark ]

Question 29

The hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary. Explain why.

Answer 29

Loss of water / loss of fluid / friction (against capillary lining).

Question 30

ATP is useful in many biological processes. Explain why.

Answer 30

Releases energy in small / manageable amounts;

1. Accept less than glucose
2. (Broken down) in a one step / single bond broken immediate energy compound / makes energy available rapidly;
3. Accept easily broken down
4. Phosphorylates / adds phosphate makes (phosphorylated substances) more reactive / lowers activation energy;
5. Do not accept phosphorus or P on its own
6. Reformed / made again

Question 31

Describe how sugar is transported from the lower leaves of the plant to the growing leaf buds at the top of the plant.

Answer 31

Sugar is transported from the lower leaves of the plant to the growing leaf buds by… Any five of the following:

Active transport/loading of sucrose from leaf into the phloem/sieve element by companion cell; [1 mark

This causes the water potential to decrease in the phloem AND so water enters by osmosis: [1 mark]

(Water entry) results in high (hydrostatic) pressure: [1 mark]

Mass flow upwards to leaf buds down the pressure gradient / from area of high pressure to area of low pressure: [1 mark]

At the leaves/leaf buds/sink sugars are (actively) unloaded SO lowering the water potential of the surrounding cells: [1 mark]

Water moves out of the sieve tube by osmosis; AND (hydrostatic) pressure in phloem decreases: [1 mark]

• Water leaving the phloem at the sink end) maintains the pressure gradient: [1 mark]

[Total: 5 marks]

Question 32

Describe the role of DNA polymerase in the semi-conservative replication of DNA.

Answer 32

1. Joins (adjacent DNA) nucleotides

2. (Catalyses) condensation (reactions);3.(Catalyses formation of) phosphodiester bonds (between adjacent nucleotides

Question 33

A gene is a small section of DNA. State what a gene codes for.

Answer 33

A gene could code for:

The amino acid sequence of a polypeptide; [1 mark]

A functional RNA product OR ribosomal RNA (rRNA) OR transfer RNA (tRNA);

[1 mark]

[Total: 2 marks]

Question 34

State and explain how an increase in temperature would affect the rate of movement of substance Y across a cell membrane.

Answer 34

An increase in temperature would have the following effect on the rate of movement of substance Y…

Increased rate of movement/diffusion; [1 mark] Because…

Increasing temperature increases the kinetic energy of molecules SO causing them to move at a faster rate; [1 mark]

[Total: 2 marks]

Question 35

Give a null hypothesis for this investigation andname a statistical test that would be appropriate to test your null hypothesis

Answer 35

1. There is no association/correlation/relationship between the concentration of carbon dioxide and the stomatal density
2. Correlation coefficient;

Question 36

From 1910 to 2000, the carbon dioxide concentration in the atmosphere increased from 300 parts per million to 365 parts per million. Use Figure 2to calculate the mean rate of change in stomatal density from 1910 to 2000. Give your answer as a number of stomata per mm2per 10-year period. Show your work`.

Answer 36

Final answer in range 2.6 ̇to 2.7
1 mark for stomatal density decrease of 24 to 25 OR Final answer of between 0.26 ̇to 0.27 ̇OR Correct calculation with incorrectly rounding taking answer out of correct range

Question 37

(a) The scientists gave an injection to a mouse to make it produce the monoclonal antibody used in this investigation (line 7).
What should this injection have contained?

(b) LDL enters the liver cells (lines 3−4).
Using your knowledge of the structure of the cell-surface membrane, suggest how LDL enters the cell.

(c) Explain how the monoclonal antibody would prevent the regulator protein from working (lines 7−8).

(d) Describe how the control group should have been treated.

Answer 37

a) Regulator protein
b) 1. Lipid soluble / hydrophobic
2. Enters through (phospholipid) bilayer
OR
3. (Protein part of) LDL attaches to receptor
4. Goes through carrier / channel protein.

c) Any two from:
1. (Monoclonal antibody) has a specific tertiary structure / variable region / is complementary to regulator protein
Do not award MP1 if reference to active site.
2. Binds to / forms complex with (regulator protein)
“It” refers to monoclonal antibody in MP1 and MP2
3. (So regulator protein) would not fit / bind to the receptor / is not complementary to receptor

d) . Injection with salt solution
1. Accept inject placebo in salt solution
2. Otherwise treated the same.

Question 38

Babies can sometimes be born with a small hole in the wall that separates the right and left ventricles of their heart. Suggest why this is a dangerous health condition.

Answer 38

Any three of the following:

• The wall (septum) separates oxygenated and deoxygenated blood; [1 mark]

If there is a hole, there will be a mixing of oxygenated and deoxygenated blood; [1 mark]

• The blood that gets pumped out of the heart will not contain as much oxygen (because some of the oxygenated blood has been replaced with deoxygenated blood from the right side of the heart) OR less (oxygenated) blood will be pumped with each beat OR there will be a drop in blood pressure; [1 mark]

The cells will not get enough oxygen; [1 mark]

Question 39

Explain the function of the elastic tissue in the wall of an artery.

Answer 39

Enables the artery wall to stretch SO that it isn’t damaged by high blood pressure;

[1 mark]

After stretching the artery walls can recoil to their original shape SO maintaining blood

pressure; [1 mark]

Question 40

) The water potential of the blood plasma is more negative at the venule end of the capillary than at the arteriole end of the capillary. Explain why.

Answer 40

1. Water has left the capillary;
2. Proteins (in blood) too large to leave capillary;
3. Increasing / giving higher concentration of blood proteins (and thus wp).

Question 41

Describe what is happening at the stage labelled Y in Figure 2.

Answer 41

Stage Y in Figure 2 shows…

The B cells are differentiating / specialising / developing into different cell types; [1 mark]

Memory cells AND plasma cells form; [1 mark]

[Total: 2 marks]

Question 42

(d) If someone has MD, the concentration of lactate in their blood after exercise is usually much higher than normal (lines 15–17). Suggest why.

Answer 42

(d) 1. Mitochondria / aerobic respiration not producing much / any ATP;
2. (With MD) increased use of ATP supplied by increase in anaerobic respiration;
3. More lactate produced and leaves muscle by (facilitated) diffusion

Question 43

Describe how a phagocyte destroys a pathogen present in the blood.

Answer 43

1. Engulfs;
2. Forming vesicle/phagosome and fuses with lysosome;
3. Enzymes digest/hydrolyse;

Question 44

A scientist used radioactive carbon dioxide to investigate the direction and rate of sucrose transport in a rose plant. His results showed that during periods of plant growth sucrose was transported mostly upwards. Explain why this is happening.

Answer 44

During periods of growth sucrose was transported mostly upwards because:

The direction of sucrose transport depends on the location of sink tissue/cells; [1 mark]

. When a plant is growing the areas undergoing cell division are the main sinks: [1 mark]

These areas are at the top of the plant OR leaf buds are above leaves; [1 mark]

[Total: 3 marks]

Question 45

Explain how the endothelium layer of the artery in part (a) in Figure 1 is adapted for the transport of blood.

Answer 45

Smooth surface SO allows blood to flow freely Ireduces friction; [1 mark] • Folded SO allows the artery to stretch (when blood volume increases); [1 mark]

Question 46

Suggest how one antibody can be complementary to both a tick protein and alpha-gal

Answer 46

1. (Part of tick protein and alpha-gal) have a similar shape/structure;
2. Antibody is complementary to both (tick protein

and alpha-gal)

OR

Antigen-binding site is complementary to both (tick protein and alpha-gal)

OR

Antibody can form antigen-antibody complex with both (tick protein and alpha-gal);`

Question 47

The Amazonian forest today contains a very high diversity of bird species.
• Over the last 2 000 000 years, long periods of dry climate caused this forest to separate into a number of smaller forests.
• Different plant communities developed in each of these smaller forests.
• Each time the climate became wetter again, the smaller forests grew in size and merged to reform the Amazonian forest.
(a) Use the information provided to explain how a very high diversity of bird species has developed in the Amazonian forest.

Answer 47

) 1. No interbreeding / gene pools are separate / geographic(al) isolation;
Accept: all marks if answer written in context of producing increased diversity of plants
1 Do not award this mark in context of new species being formed and then not interbreeding
1 Accept reproductive isolation as an alternative to no interbreeding
2. Mutation;
2 Accept: genetic variation
3. Different selection pressures / different foods / niches / habitats;
3 Accept: different environment / biotic / abiotic conditions or named condition
3 Neutral: different climates
4. Adapted organisms survive and breed / differential reproductive success;
5. Change / increase in allele frequency / frequencies;

Question 48

The scientists’ hypothesis was that an earlier immune response to tick protein causes the allergic reaction.

Consider whether Figure 7 supports this hypothesis.

Answer 48

1. Exposure to tick (protein) is followed by increase in antibody (specific to alpha-gal);

3 max

2. (Later) greater/faster increase in antibody suggests there are memory cells;
3. Antibody (specific to alpha-gal) increases

during/after allergic reaction;

4. During/after allergic reaction, total antibody

increases more than alpha-gal antibody

5. (So) may be other antibodies (that are causing

allergic reaction);

Question 49

Describe the role of haemoglobin in supplying oxygen to the cells of the human body.

Answer 49

of the following:

Haemoglobin binds with oxygen to produce oxyhaemoglobin; [1 mark] Haemoglobin is loaded/ takes up / associates/binds with oxygen in an area of higher ppo,/ gas exchange surface / lungs; [1 mark]

Oxygen is unloaded/released in an area of lower pp02/capillaries/cells / tissues;

[1 mark]

Question 50

Explain five properties that make water important for organisms.

Answer 50

1. A metabolite in condensation/hydrolysis/ photosynthesis/respiration;
2. A solvent so (metabolic) reactions can occur

OR

A solvent so allowing transport of substances;

3. High heat capacity so buffers changes in temperature;
4. Large latent heat of vaporisation so provides a cooling effect (through evaporation);
5. Cohesion (between water molecules) so supports columns of water (in plants);
6. Cohesion (between water molecules) so produces surface tension supporting (small) organisms;

Question 51

A patient recovered from an influenza infection, and their blood was found to contain influenza antibodies 6 months later. Explain why this patient was able to catch influenza again several days after their blood tested positive for flu antibodies.

Answer 51

The patient was able to catch influenza again despite having antibodies in their blood because:

Influenza viruses show antigen variability/antigenic variability; [1 mark]

So the antibodies will no longer be complementary to the influenza antigen; [1 mark]

[Total: 2 marks]

Question 52

List three other dissolved substances which are also present in blood plasma.

Answer 52

Oxygen; [1 mark]

⚫ Urea; [1 mark]

⚫ Carbon dioxide; [1 mark]

Mineral ions; [1 mark]

Hormones; [1 mark]

⚫ Amino acids; [1 mark]

Question 53

Describe the structure of proteins.

Answer 53

1. Polymer of amino acids;
2. Joined by peptide bonds;
3. Formed by condensation;
4. Primary structure is order of amino acids;
5. Secondary structure is folding of polypeptide chain due to hydrogen bonding;

Accept alpha helix / pleated sheet

6. Tertiary structure is 3-D folding due to hydrogen bonding and ionic / disulfide bonds;
7. Quaternary structure is two or more polypeptide chains

Question 54

Tetanus is a bacterial infection gained from contact between the blood and soil-dwelling bacteria Clostridium tetani. An individual who had not been vaccinated against tetanus received a cut from a garden fork and it was suggested that they should go to the hospital for an injection of tetanus antibodies. State how this injection would protect them against tetanus.

Answer 54

Any two of the following:

The antibodies would be present immediately / be able to act instantly; [1 mark] The antibodies would bind to the antigens on the tetanus bacteria; [1 mark]

The tetanus bacteria would be destroyed / would be unable to spread / would undergo phagocytosis; [1 mark]

[Total: 2 marks]

Question 55

Cholesterol increases the stability of plasma membranes. Cholesterol does this by making membranes less flexible.

(f) Suggest one advantage of the different percentage of cholesterol in red blood cells compared with cells lining the ileum.

Answer 55

Red blood cells free in blood / not supported by other cells so cholesterol helps to maintain shape

Question 56

Fill in the blanks below.

Tissue fluid is the liquid which surrounds cells. At the start of the capillary bed, the hydrostatic pressure in the capillary is _________ than the hydrostatic pressure within the tissue fluid. This difference in pressure forces fluid to ________ the capillaries and move into the surrounding tissues _________ molecules such as water, oxygen and nutrients pass through the capillary bed and into the tissue fluid.

Answer 56

The hydrostatic pressure in the capillary is…

Greater/higher; [1 mark]

The difference in pressure forces fluid to…

Exit/leave; [1 mark] Small/smaller; [1 mark]

…molecules such as water, oxygen and nutrients..

Question 57

The action of the carrier protein Xin Figure 1is linked to a membrane-bound ATP hydrolase enzyme.Explain the function of this ATP hydrolase.

Answer 57

1. (ATP to ADP + Pi ) Releases energy;Reject ‘produces/makes/creates energy’.
2. (energy) allows ions to be moved against a concentration gradient OR (energy) allows active transport of ions;

For ‘ions’ accept Na+or K+.Do not accept if this movement is of glucose not ions.

Question 58

Describe and explain one property of visking tubing (sometimes called dialysis tubing) that makes it a good choice for experiments that model the action of enzymes in the gut.

Answer 58

(Visking tubing) is partially/selectively permeable; [1 mark]

SO small molecules can diffuse through/large molecules cannot diffuse through; [1 mark]

Total: 2 marks]

Question 59

Suggest how the amino acids at positions 35 and 52 are held close together to form the active site.

Answer 59

idea that amino acid chain folds/tertiary structure; named bond holding tertiary structure e.g. ionic disulphide hydrogen;

Question 60

) A mutation can lead to the production of a non-functional enzyme. Explain how.

Answer 60

1. Change / mutation in base / nucleotide sequence (of DNA / gene); Q.
   Ignore: references to changing base-pairing
   Accept: affect for change, if in correct context Accept: changes triplets / codons
2. Change in amino acid sequence / primary structure (of enzyme); Accept: different amino acid(s) coded for
   Q Reject: different amino acids produced / formed / made
3. Change in hydrogen / ionic / disulfide bonds; Accept: references to sulfur bonds
4. Change in the tertiary structure / shape;
   Neutral: alters 3D structure / 3D shape
5. Change in active site;
6. Substrate not complementary / cannot bind (to enzyme / active site) / no enzyme-substrate complexes form.

Question 61

(e) A small amount of DNA can be extracted from mitochondria and DNA sequencing used to try to find a mutation (lines 18–19).
From this sample:
• how would enough DNA be obtained for sequencing?
• how would sequencing allow the identification of a mutation?

Answer 61

1. Enough DNA using PCR;
2. Compare DNA sequence with ‘normal’ DNA.

Question 62

List four ways in which the structure of capillaries are adapted to act as exchange surfaces.

Answer 62

Permeable wall (NOT cell wall/membrane); [1 mark]

Thin walls OR walls one cell thick; [1 mark]

Flat/thin/squamous endothelial cells: [1 mark)

Narrow/small diameter/small lumen: [1 mark] Red blood cells are in contact with the capillary wall OR pass singly: [1 m

Question 63

The process by which food is pushed along the oesophagus and small intestine is…

Answer 63

Peristalsis:

Question 64

Some cancer cells have a receptor protein in their cell-surface membrane that binds to a hormone called growth factor. This stimulates the cancer cells to divide.
Scientists have produced a monoclonal antibody that stops this stimulation.
Use your knowledge of monoclonal antibodies to suggest how this antibody stops the growth of a tumour.

Answer 64

(b) 1. Antibody has specific tertiary structure / binding site / variable region; Do not accept explanations involving undefined antigen
2. Complementary (shape / fit) to receptor protein / GF / binds to receptor protein / to GF;
Ignore: same shape as receptor protein / GF
3. Prevents GF binding (to receptor).
3

Question 65

Explain the steep gradient seen in the curve seen for HbA in Figure 1.

Answer 65

The first oxygen that binds haemoglobin causes a change in shape / conformational change: [1 mark]

The change in the shape of haemoglobin allows more O, to bind / O, to bind more easily

/ an increase in the rate of O, binding: [1 mark]

Question 66

State the events that need to take place for the mature B lymphocyte in Figure 1 to be activated. Note that the term ‘activated’ here refers to the stimulation needed to initiate cell division by mitosis.

Answer 66

The events that need to take place to activate a B cell are…

The cell surface antibody/molecule X binding/attaching to its complementary/specific antigen; [1 mark]

• The release of cytokines/chemical signals from a T helper cell; [1 mark]

[Total: 2 marks]

Question 67

The diagram shows apparatus used in breaking down sucrose. The enzyme sucrase is fixed to inert beads. Sucrose solution is then passed through the column.

Describe a biochemical test to find out if the solution collected from the apparatus contains

Answer 67

(i) heat with Benedict’s solution (disqualify if HCl added); orange / brown / brick red / green / yellow colour or precipitate;
(ii) biuret test / NaOH + CuSO4; purple / violet / lilac / mauve;

Question 68

Larger multicellular organisms have specialised cells and tissues that form mas transport systems. Why do they need a mass transport system?

Answer 68

of the following:

Diffusion would be too slow to transport substance around the organism; [1 ma Diffusion distances are much longer/larger than in smaller organisms: [1 mark] Metabolic demands/needs of tissues would not be met; [1 mark]

Question 69

Describe the gross structure of the human gas exchange system and how we breathe in and out.

Answer 69

1. Named structures-trachea, bronchi, bronchioles, alveoli;
2. Above structures named in correct order
3. Breathing in-diaphragm contracts and external intercostal muscles contract
4. (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in);
5. Breathing out-Diaphragm relaxes and internal intercostal muscles contract; Accept diaphragm relaxes and (external) intercostal muscles relax and lung tissue is elastic (so recoils).
6. (Causes) volume decrease and pressure increase in the thoracic cavity (to above atmospheric, resulting in air moving out);

Question 70

Suggest and explain one other factor the manufacturers should consider when deciding on the best enzyme to include in the biological washing powder.

Answer 70

The optimum pH of the enzymes; [1 mark]

• Because pH can affect the 3D / tertiary structure of the enzymes: [1 mark]

OR

The concentration of the enzyme; [1 mark]

Because the concentration of the enzyme will affect the rate of the reaction/ how

effective the enzyme is at removing the stain: [1 mark]

Question 71

Describe the role of antibodies in producing a positive result in an ELISA test

Answer 71

1. (First) antibody binds/attaches /complementary (in shape) to antigen;
2. (Second) antibody with enzyme attached is added;
3. (Second) antibody attaches to antigen; Accept (second) antibody attaches to (first) antibody (indirect ELISA test).
4. (Substrate/solution added) and colour changes;

Question 72

After the disease is diagnosed, monoclonal antibodies are used in some medical treatments. Give one example of using monoclonal antibodies in a medical treatment

Answer 72

Block antigens/receptors on cells;

Question 73

The mass flow hypothesis is used to explain the movement of substances through phloem.

Use your understanding of the mass flow hypothesis to explain how pressure is

generated inside this phloem tube.

Answer 73

1. Sucrose actively transported (into phloem); 2. Lowering/reducing water potential

OR

More negative water potential; 3. Water moves (into phloem) by osmosis (from xylem);

Question 74

Describe how a non-competitive inhibitor can reduce the rate of an enzyme-controlled reaction.

Answer 74

1. Attaches to the enzyme at a site other than the active site;

Accept ‘attaches to allosteric/inhibitor site’

2. Changes (shape of) the active site

OR

Changes tertiary structure (of enzyme);

3. (So active site and substrate) no longer complementary so less/no substrate can fit/bind;

Question 75

(c) The percentage of the population vaccinated does not need to be 100% to be effective in preventing the spread of whooping cough

Answer 75

1. Q Do not accept disease for pathogen
2. So susceptible / unvaccinated people less likely to contact infected people.
   2

Question 76

Use your knowledge of lipid digestion to explain the differences in the results for samples A and B shown in the table above. You should assume that no absorption had occurred.

Answer 76

1. Triglycerides decrease because of the action of lipase OR Fatty acids increase because of the action of lipase

;2. Triglycerides decrease because of hydrolysis (of triglycerides)ORFatty acids increase because of hydrolysis (of triglycerides)

3.Triglycerides decrease because of digestion of ester bonds (between fatty acid and glycerol)ORFatty acids increase because of digestion of ester bonds (between fatty acid and glycerol);

Question 77

Mucus also contains glycoproteins. One of these glycoproteins is a polypeptide with the sugar, and lactose, attached. Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein

Answer 77

1. Glucose and galactose; Ignore α or β for glucose
2. Joined by condensation (reaction);
3. Joined by glycosidic bond;
4. Added to the polypeptide in Golgi (apparatus)

Question 78

Do the data in the graph above show a linear relationship between the concentration of particulate matter and the percentage of dead cells? Use suitable calculations to justify your answer.

Answer 78

(No)
EITHER 1.9 (percent per 5 μg cm–3);
2.1.42/1.8 (percent per 5 μg cm–3);

Question 79

After collecting the samples, the scientist immediately heated them to 70 °C for 10 minutes. Explain why.

Answer 79

1. To denature the enzymes/lipase;

Accept description of denaturation in terms of change in tertiary structure.

2.So no further digestion/hydrolysis/catalysis occurred; Accept ‘break down’ for digestion

Question 80

Describe and explain twofeatures you would expect to find in a cell specialised for absorption.

Answer 80

1.Folded membrane/microvilli solarge surface area (for absorption);

Reject references to ‘villi’.Accept ‘brush border’ for ‘microvilli’.

2.Large number of co-transport/carrier/channel proteins sofast rate (of absorption)
OR Large number of co-transport/carrier proteins foractive transport
OR Large number of co-transport/carrier/channel proteins forfacilitated diffusion;

3. Large number of mitochondria so make (more) ATP (by respiration) OR Large number of mitochondria for aerobic respiration OR Large number of mitochondria torelease energy for active transport;
4. Membrane-bound (digestive) enzymes somaintains concentration gradient (for fast absorption);Accept named examples of digestive enzymes

Question 81

Explain how cellulose molecules are adapted for their function in plant cells.

Answer 81

1. Long and straight chains;
2. Become linked together by many hydrogen bonds to

form fibrils;

3. Provide strength (to cell wall);

Question 82

(e) The ecologists expected to obtain the same result from their calculations of the number of insects on this island on each day during the period 1–5 days after release. In fact, their estimated number increased after day 1.
During the same period, the number of insects they caught decreased.
The method used by the ecologists might have caused these changes.
Use the information provided to suggest one way in which the method used by the ecologists might have caused the increase in their estimates of the size of the insect population.

Answer 82

(e) 1. Scientists removed large numbers of insects (which were not returned) from same area / same population;
2. Affecting ratio of marked to unmarked.

Question 83

Describe the pathway taken by an oxygen molecule from an alveolus to the blood.

Answer 83

1. (Across) alveolar epithelium;
2. Endothelium / epithelium of capillary;

Incorrect sequence = maximum of 1 mark

Diffuses

Question 84

At Qon the diagram above there is a small increase in pressure and rate of blood flow in the aorta. Explain how this happens and its importance.

Answer 84

1. Elastic recoil (of the aorta wall/tissue); Reject muscle contracting. Ignore reference to muscle relaxing.
2. Smooths the blood flow OR Maintains rate of blood flow OR Maintains blood pressure;

Question 85

Starch molecules and cellulose molecules have different functions in plant cells. Each molecule is adapted for its function.

Explain one way in which starch molecules are adapted for their function in plant cells.

Answer 85

1. Insoluble;
2. Don’t affect water potential;

OR

3. Helical;

Accept form spirals

4. Compact;

OR

5. Large molecule;
6. Cannot leave cell

Question 86

Phicem pressure is reduced during the hottest part of the day. Use information in Figure 6 along with your understanding of transpiration and mass flow to explain why

Answer 86

1. High (rate of).transpiration/evaporation; 2. Water lost through stomata

OR

(High) tension in xylem.

3. (Causes) less water movement from xylem to

phloem OR

Insufficient water potential in phloem to draw water from xylem,

Question 87

Describe the functions of the vascular bundles of plants.

Answer 87

The functions of the vascular bundles of plants include:

The transport of water from the roots to the leaves; [1 mark]

The transport of minerals/named mineral from the roots to the leaves; [1 mark]

The transport of sucrose/carbohydrates/assimilates from the leaves to where they are stored OR from where they are stored to growing parts of the plant OR from source to sink; [1 mark]

[Total: 3 marks]

Question 88

High blood pressure leads to an accumulation of tissue fluid. Explain how.

Answer 88

1. High blood pressure = high hydrostatic pressure;
2. Increases outward pressure from (arterial) end of capillary / reduces inward pressure at (venule) end of capillary;
3. (So) more tissue fluid formed / less tissue fluid is reabsorb

Question 89

a) Name the membrane transport processes taking place at A and B in Figure 2.

b) State the purpose of the process taking place at the position labelled C in Figure 2.

Answer 89

a) A - Co-transport
B - Facillitated diffusion

b) The process taking place at C is important because…

It maintains / creates the concentration gradient for sodium (between the small intestine and the inside of the epithelial cell); [1 mark]

Question 90

Explain how one feature of an alveolus allows efficient gas exchange to occur.

Answer 90

one cell thick;

Reject thin membrane

2. Creating a short diffusion pathway / reduces the diffusion distance;

Question 91

Eukaryotic cells produce and release proteins.Outline the role of organellesin the production, transport and release of proteins from eukaryotic cells.

Answer 91

1. DNA in nucleus is code (for protein);
2. Ribosomes/rough endoplasmic reticulum produce (protein);Accept rER for ‘rough endoplasmic reticulum’
3. Mitochondria produce ATP (for protein synthesis);
4. Golgi apparatus package/modify;ORCarbohydrate added/glycoprotein produced by Golgi apparatus;Accept body for ‘apparatus’
5. Vesicles transport OR Rough endoplasmic reticulum transports;
6. (Vesicles) fuse with cell(-surface) membrane;Accept exocytosis at cell me

Question 92

Q4.Ecologists investigated the size of an insect population on a small island. They used a mark-release-recapture method. To mark the insects they used a fluorescent powder. This powder glows bright red when exposed to ultraviolet (UV) light.
(a) The ecologists captured insects from a number of sites on the island. Suggest how they decided where to take their samples.

Answer 92

1. Draw grid over (map of) area;
2. Select squares / coordinates at random.

Question 93

(ii) Suggest an explanation for the relationship between the concentration of herbicide and the mean crop yield.

(iii) Explain the relationship between the concentration of herbicide and the mean index of diversity of insects.

Answer 93

(ii) 1. (More) weeds killed so more crops / plants survive / higher yield / less competition;
2. High concentrations (of herbicide) harm / damage / kill / are toxic to crops / plants

(iii) 1. Reduced plant diversity / fewer plant species / fewer varieties of plant;
Accept: ‘weed’ for ‘plant’
Neutral: fewer plants
Accept: only one crop species remains
2. Fewer habitats / niches;
Q Neutral: fewer homes / shelters
3. Fewer food sources / varieties of food;
Neutral: less food

Question 94

Explain the advantage to a person with anaemia of the change shown in the oxygen dissociation curve in Figure 1.

Answer 94

three of the following:

The curve (for the anaemic person) has shifted to the right SO their haemoglobin has a lower affinity for oxygen; [1 mark]

• The anaemic haemoglobin releases more oxygen OR oxygen is released more quickly

OR oxygen dissociates/unloads more readily: [1 mark] This oxygen is then available for use in aerobic respiration: [1 mark]

• The demand for ATP/energy can be met even at a lower haemoglobin concentration; [1 mark]

Question 95

The scientists expressed their results as Percentage of lipid in plasma membrane by mass. Explain how they would find these values.

Answer 95

1. Divide mass of each lipid by total mass of all lipids (in that type of cell);
2. Multiply answer by 100;

Question 96

Explain the difference between the rate at which bubbles were produced in.

(i) tubes A and B;
(ii) tubes A and D.
b) Explain the purpose of tube C.

Tube Substance added Rate at which bubbles of oxygen were produced

A Piece of liver 4

B Ground liver and sand 5

C Sand 0

D Piece of cooled, boiled liver 0

Answer 96

(i) (Grinding) breaks open cells / increases surface area (of liver);

Releases catalase / enzyme / more catalase / allows more hydrogen peroxide into liver;

2

(ii) Heating causes bonds (maintaining tertiary structure) to break; Denatures / changes tertiary structure so active site changed; Substrate no longer fits / ES complex not formed;

3

(b) (Control) to show that sand did not affect reaction (with ground liver);

Question 97

Use the graph to explain why

(i) hydrogen peroxide breaks down at a lower temperature when catalase is present than when it is not present;

Answer 97

Lower activation energy / less energy required to bring about reaction;

Question 98

Describe what happens to the muscle tension of the different heart chambers during the

events of the cardiac cycle.

Answer 98

The muscle of the atria (accept atrium) contracts; [1 mark]

⚫ (Then) the muscle of the ventricles contracts; [1 mark]

⚫ (Then) all of the heart muscle / atria and ventricular muscle relaxes; [1 mark]

[Total: 3 marks]

Question 99

The movement of Na+outof the cell allows the absorption of glucose intothe cell lining the ileum.Explain how.

Answer 99

1.(Maintains/generates) a concentration/diffusion gradient for Na+(from ileum into cell);

Accept ‘(Maintains/generates) a lower concentration of Na+inside the cell compared with outside the cell’

.2.Na+moving (in) by facilitateddiffusion, brings glucose with itORNa+moving (in) by co-transport, brings glucose with it;Accept ‘co-transporter’ for ‘co-transport

Question 100

List three features of xylem vessels that make them specialised for the transport of water.

Answer 100

Any three of the following:

The cells contain no cytoplasm; [1 mark]

Cell walls are reinforced with lignin/are lignified; [1 mark]

Water can move between vessels via small gaps called pits in the side walls; [1 mark]

The end walls are broken down meaning the cells form continuous pipes; [1 mark]

[Total: 3 marks]

Question 101

Some tumour cells contain higher than normal concentrations of cyclin D.Use the graph above to suggest why higher than normal concentrations of cyclin D could result in a tumour.

Answer 101

1. Shortens interphase OR Cells begin DNA replication earlier OR DNA replication (starts) faster;Accept ‘start mitosis earlier’.
2. Fast(er) cellcycle/division/multiplication/mitosis
3. (Resulting in) a mass/group of abnormal/excessive cells;

Question 102

Give two ways in which pathogens can cause disease

Answer 102

Releases) toxins; 2. Kills cells / tissues.

Question 103

The results for the leaves in set X are different from the leaves in set Y. Suggest an explanation for this.

Answer 103

Petroleum jelly is covering/blocking the stomata; [1 mark]

Reduces water lost by evaporation/transpiration; [1 mark]

Question 104

E. coli has no cholesterol in its cell-surface membrane. Despite this, the cell maintains a constant shape. Explain why.

Answer 104

1. Cell unable to change shape;
2. (Because) cell has a cell wall;
3. (Wall is) rigid / made of peptidoglycan / murein;

Question 105

What is absorption

Answer 105

Absorption is…

The transport of small, soluble molecules across cell membranes: [1 mark]

Into the bloodstream; [1 mark]

Question 106

Constrast prokaryotic vs eukaryotic

Answer 106

2. A has a nucleus whereas B has free DNA; 3. A has mitochondria whereas B does not;
3. A has Golgi body/endoplasmic reticulum whereas B

does not; 5. A has no cell wall whereas B has a murein/glycoprotein

cell wall; 6. A has no capsule whereas B has a capsule;

7. A has DNA is bound to histones/proteins whereas B has DNA not associated with histones/proteins

OR

A has linear DNA whereas B has circular DNA;

8. A has larger ribosomes;

Question 107

Use this information and Figure 2 to suggest how eating its own caecal droppings helps a rabbit’s digestion and absorption of dietary protein.

Answer 107

1. More/remaining/undigested (protein) broken

down; 2. (So more) amino acids absorbed;

3

1. 3
2. (Because) protein/food passes again through stomach/ileum;

Question 108

Give two types of cells, other than pathogens, that can stimulate an immune response.

Answer 108

1.(Cells from) other organisms/transplants;2

.Abnormal/cancer/tumour (cells);3.(Cells) infected by virus;

Question 109

5 types of transport through cells

Answer 109

1. (Simple) diffusion of small/non-polar molecules down a concentration gradient;
2. Facilitated diffusion down a concentration gradient via protein carrier/channel;
3. Osmosis of water down a water potential gradient;
   4: Active transport against a concentration gradient via protein carrier using ATP
4. Co-transport of 2 different substances using a carrier protein,

Question 110

Some cancer cells have a receptor protein in their cell-surface membrane that binds to a hormone called growth factor. This stimulates the cancer cells to divide.
Scientists have produced a monoclonal antibody that stops this stimulation.
Use your knowledge of monoclonal antibodies to suggest how this antibody stops the growth of a tumour.

Answer 110

1. Antibody has specific tertiary structure / binding site / variable region; Do not accept explanations involving undefined antigen
2. Complementary (shape / fit) to receptor protein / GF / binds to receptor protein / to GF;
   Ignore: same shape as receptor protein / GF
3. Prevents GF binding (to receptor).

Question 111

test tubes A and B became warmer when the reaction was taking place.

Answer 111

Energy in products / water and oxygen less than energy in substrate / reactants / hydrogen peroxide; (Difference) given out as heat / exothermic;

Question 112

d) Most of the sugars produced by plants are used up rapidly in respiration. However, sometimes plants can overproduce sugars during photosynthesis. Excess sucrose in the sink tissues can be converted to starch. Suggest the benefits of this for maintaining the mass flow system.

Answer 112

The benefits to the mass flow system of converting excess sugars to starch are:

Starch is insoluble OR has no osmotic effect; [1 mark]

Starch doesn’t cause water to leave the phloem by osmosis SO pressure gradient is maintained / doesn’t affect pressure gradient; [1 mark]

Question 113

When setting up the potometer in Figure 1, one of the precautions the students took to ensure reliable measurements of water uptake was to cut the shoots underwater. Suggest a reason for this.

Answer 113

To prevent air (bubble) entering the xylem; [1 mark]

Question 114

Arteries near the heart have a high proportion of elastic fibres compared to muscle Fibres in their walls, allowing them to absorb the shock waves caused by the pumping of the heart. Arterioles however tend to have a higher proportion of muscle fibres compared to elastic fibres. Suggest why this would be beneficial during exercise.

Answer 114

Any two of the following:

• Smooth muscle layer in arterioles can contract to control blood flow OR partially shut off blood flow: [1 mark]

• Allows the delivery of blood to be targeted/prioritised towards muscles; [1 mark] • During exercise blood flow to the stomach and intestines is reduced; [1 mark]

Increased blood flow (to the muscles) means more glucose and oxygen for aerobic respiration; [1 mark]

Question 115

Explain why the vaccine causes an increase in antibody concentration.

Answer 115

The vaccine causes an increase in antibody concentration because…

• The vaccine contains the antigen (from the pathogen); [1 mark]

The antigen activates T helper cells/ causes T helper cells to release chemical signals / activates B lymphocytes/ causes B lymphocytes to develop into plasma cells; [1 mark]

Plasma cells produce antibodies; [1 mark]

[Total: 3 marks]

Question 116

Suggest why a nucleus is not visible in above image.

Answer 116

A section/slice (so nucleus in another part of cell)OR(Nucleus) not stained

Question 117

The diagram below shows pressure and blood flow during the cardiac cycle in a dog
At Pon the diagram above, the pressure in the left ventricle is increasing. At this time, the blood flow rate has not yet started to increase in the aorta. Use evidence from the diagram above to explain why.

Answer 117

1. Aortic/semi-lunar valves are closed; Accept ‘aorta valve’ or ‘valve to the aorta’ or ‘valve between the aorta and the ventricle’.Do not accept S-L/A-V valve.
2. Because the pressure in the aorta is higher than in the ventricle

Question 118

Explain why structure A in Figure 1 forms in the aqueous (watery) environment of the cell cytoplasm.

Answer 118

Structure A forms in an aqueous environment because…

• The (phospholipid) molecules have a hydrophilic head AND a hydrophobic tail; [1 mark]

The molecules arrange themselves so that contact between the (hydrophobic) tails and the surrounding water is minimised; [1 mark]

[Total: 2 marks]

Question 119

Fill in the blanks to accurately describe the mechanism of sugar transport in plant stems.

________ is actively transported into the phibem by a group of specialised cells. The increased solute concentration causes the water potential to _________ in phloem and so water enters by______ and This results in a high ___gradient causing a mass flow of water and sugar towards the _________ of the plant where the sugars are __________

Answer 119

• Sucrose/sugars/assimilates/amino acids: [1 mark]… is actively transported into the phloem

The increased sugar concentration causes the water potential to… decrease/go down/reduce; [1 mark]

Water enters by… osmosis; [1 mark]

This results in a high…pressure/hydrostatic pressure: [1 mark]

Causing a mass flow of water and sugars towards the… sink/storage tissue: [1 mark]

Where the sugars are… unloaded OR used for respiration OR stored; [1 mark]

Question 120

Use the information in Figure 1 to explain the formation of tissue fluid.

Answer 120

Tissue fluid formation takes place because:

There is an overall outward pressure of 3.2 kPa (from the capillary out into the surrounding tissue); [1 mark]

This causes small molecules (such as water, oxygen, glucose) to be forced out of capillary (at arteriole end of capillary); [1 mark]

Question 121

State the two main roles of bile in digestion.

Answer 121

To neutralise stomach acid (by being alkaline); [1 mark]

To emulsify fats; [1 mark]

Question 122

Hydrogen bonds form between polar water molecules. Describe the role that hydrogen bonding plays in the cohesion-tension theory of water transport in the xylem of plants.

Answer 122

Any three of the following:

Water is lost from the leaf due to transpiration/evaporation of water / diffusion of water from leaf cells; [1 mark]

Polar water molecules cohere/stick together by hydrogen bonds; [1 mark]

This forms a (continuous) water column; [1 mark]

There is adhesion of water (molecules) to xylem walls; [1 mark]

Meaning (A column of) water can be pulled up the xylem vessels; [1 mark]

[Total: 3 marks]

Question 123

2 What can you conclude about the absorption of the products of protein digestion as the percentage of protein increased in the rabbits’ food?

Answer 123

1. No significant difference (in protein absorption);
2. (because + 2) SDs overlap;
3. (So mean) percentage absorbed not affected by percentage in diet,

Amount of protein (in diet) is not a limiting factor

OR

01.2

Something else is limiting factor eg amount of protease:

5. (But) small range of protein in diet OR (Should) Investigate wider range:

Question 124

Use Figure 3 to suggest how a vaccine could be effective against the development of cancer.

Answer 124

A vaccine could be effective against the development of cancer by:

Any four of the following:

The vaccine would contain the antigens of a cancer/tumour cell OR DNA/mRNA that codes for antigens of a cancer/tumour cell; [1 mark]

T cells/B cells bind to the cancer antigens with specific, complementary receptors;

[1 mark]

B cells are activated/stimulated and produce antibodies specific to the cancer/tumour

cells; [1 mark]

The antibodies bind to the cancer/tumour cells, leading to their destruction/death (by

phagocytosis): [1 mark]

• Memory cells remain in the blood, allowing faster production of antibodies in the blood if the same cancer begins to develop again; [1 mark]

[Total: 4 marks]

Question 125

A student concluded from Figure 2 that didn’t whether girls were given two doses of vaccine or three. Evaluate this conclusion.

Answer 125

Arguments in support of the student’s conclusion:

Ques

.There is only a small difference in mean antibody concentration SO the difference may not be statistically significant; [1 mark]

AND

Arguments against the student’s conclusion:

Any two of the following:

No statistical analysis has been carried out, so we cannot be sure that there is no

significant difference between the doses; [1 mark]

Two doses appear to give a higher mean antibody concentration, so two doses may be a more effective dose; [1 mark]

Girls may be more likely to get vaccinated if they only need to have two doses; [1 mark]

[Total: 3 marks]

Question 126

A journalist saw Figure 2and suggested that future increases in atmospheric carbon dioxide concentration could result in less transpiration. Evaluate his suggestion

Answer 126

1. Increasing carbon dioxide (concentration) shows decreased stomatal density.
2. Fewer stomata means less transpiration OR Fewer stomata means less evaporation (of water from leaves) OR Fewer stomata means less diffusion of water vapour (from leaves);
3. Same (volume of) carbon dioxide can be absorbed for photosynthesis with a smaller number of stomata;
4. Don’t know the size of the stomata
5. Don’t know whether the leaf size has changed;
6. Don’t know if this is true for all species (of the plant);
7. Don’t know how long the stomata are open for
8. Don’t know if this trend will continue (beyond the concentrations of carbon dioxide shown in Figure 2);

Question 127

A disulfide bridge is labelled in the diagram above. What is the role of the disulfide bridge in forming the quaternary structure of an antibody?

Answer 127

Joins two (different) polypeptides;

Question 128

A student correctly plotted the right ventricle pressure on the same grid as the left ventricle pressure in the diagram above. Describe one way in which the student’s curve would be similar and one way it would be different from the curve shown in the diagram above.

Answer 128

1. Peaks/contractions at the same/similar time OR Same/similar pattern;Mark the answer as a whole.Accept ‘shape (of curve)’ for ‘pattern’.
2. Lower pressure

Question 129

Why does the heart require its own blood supply?

Answer 129

Blood supplies/carries oxygen OR glucose; [1 mark]

⚫ The heart tissue is made up of muscle that needs to contract; [1 mark]

⚫ (Muscle contraction) requires energy/ATP from aerobic respiration; [1 mark]

[Total: 3 marks]

Question 130

Scientists investigated the percentages of different types of lipid in plasma membranes from different types of cell. The table shows some of their results.

The scientists expressed their results as Percentage of lipid in plasma membrane by mass. Explain how they would find these values.

Answer 130

1. Divide mass of each lipid by total mass of all lipids (in that type of cell);
2. Multiply answer by 100;

Question 131

The cell in Figure 1 ends the process shown with the action of exocytosis. Describe one other way that a white blood cell might end the same process, and state why it would do this.

Answer 131

The white blood cell might…

• Display the broken down pieces of the pathogen on its cell surface membrane / become an antigen-presenting cell; [1 mark]

The reason for this is to…

Allow the pathogen to be recognised by lymphocytes / activate lymphocytes / activate the specific immune response; [1 mark]

[Total: 2 marks]

Question 132

Bile emulsifies fats. Explain what ‘emulsifies’ means.

Answer 132

Breaking fat droplets down into smaller droplets / increasing the overall surface area of the fat droplets (ahead of the action of lipase); [1 mark]

Question 133

Two couples, couple A and couple B, had one or more children affected by a mitochondrial disease. The type of mitochondrial disease was different for each couple.
None of the parents showed signs or symptoms of MD.
• Couple A had four children who were all affected by an MD.
• Couple B had four children and only one was affected by an MD.
(b) Use the information in lines 5–9 and your knowledge of inheritance to suggest why:
• all of couple A’s children had an MD
• only one of couple B’s children had an MD.

Answer 133

(b) Couple A,
1. Mutation in mitochondrial DNA / DNA of mitochondrion affected;
2. All children got affected mitochondria from mother;
3. (Probably mutation) during formation of mother’s ovary / eggs;
Couple B,
4. Mutation in nuclear gene / DNA in nucleus affected;
5. Parents heterozygous;
6. Expect 1 in 4 homozygous affected.

Question 134

explain how a non-competitive inhibitor would decrease the rate of the reaction catalysed by this enzyme.

Answer 134

idea that non-competitive inhibitor(C) binds at a site not the active site; binding causes a change in the shape of the active site; substrate is no longer able to bind to the active site;

Question 135

Explain why specific base pairing is important in DNA replication.

Answer 135

identical/exact copies made; same base sequence as original DNA; both strands act as template/complementary base pairing occurs on both strands;

Question 136

(ii) The ecologists also determined the index of diversity of lizards in an oil palm plantation next to the woodland area. They found fewer species of plant in the oil palm plantation. Lizards feed on plants and insects.
Explain why fewer species of plant would lead to fewer species of lizard in the oil palm plantation.

Answer 136

1. (So) few(er) habitats / niches;
   Ignore habitat size
   Q Neutral: fewer homes
2. (So) lower diversity of insects / fewer insect species / fewer insect types;
   Q Neutral: fewer insects
   Accept less variety of insects
3. (So) fewer food sources / less variety of food.
   Q Neutral: less food
   Ignore references to pesticides, farmers’ actions, competition between lizards and evolution

Question 137

Mucus produced by epithelial cells in the human gas exchange system contains triglycerides and phospholipids.

Compare and contrast the structure and properties of triglycerides and phospholipids.

Answer 137

1. Both contain ester bonds (between glycerol and fatty acid); All statements must be clearly comparative or linked by the candidate, not inferred from separate statements. Accept mark points shown on adjacent annotated diagrams.
2. Both contain glycerol;
3. Fatty acids on both may be saturated or unsaturated;
4. Both are insoluble in water;
5. Both contain C, H and O but phospholipids also contain P; Must relate to element.
6. Triglyceride has three fatty acids and phospholipid has two fatty acids plusphosphate group;
7. Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region;

Accept ‘non-polar’ for hydrophobic and ‘polar’ for hydrophilic.

8. Phospholipids form monolayer (on surface)/micelle/bilayer (in water) but triglycerides don’t;

Question 138

What is a monoclonal antibody

Answer 138

Antibodies with the) same tertiary structure

Question 139

The salivary glands and the pancreas both act as glands in the process of digestion. State what is meant by the term, ‘gland’ in the context of digestion.

Answer 139

A gland, in the context of digestion, is…

e An organ that releases/produces/secretes enzymes/mucus/other chemicals; [1 mark]

THAT ARE added to food / secreted into the flow of food to aid physical/chemical digestion/flow of food; [1 mark]

[Total: 2 marks]

Question 140

Describe the role of enzymes in the digestion of proteins in a mammal.

Answer 140

1. (Reference to) hydrolysis of peptide bonds, 2. Endopeptidase act in the middle of protein/polypeptide OR

4

Endopeptidase produces short(er) polypeptides/ increase number of ends; 3. Exopeptidases act at end of protein/polypeptide OR

Exopeptidase produces dipeptides/amino acids;

4. Dipeptidase acts on dipeptide/between two

amino acids

OR

01.1

Dipeptidase produces (single) amino acids:

Question 141

a) The substances that cause the food stains are usually large insoluble proteins. Explain how a biological washing powder removes these stains.

b) A journalist wi’s investigating the claims by washing powder manufacturers that stated their product removes all tough stains. Figure 1 shows their results. Use the information in Figure 1 to evaluate the manufacturers claim.

Answer 141

a) Biological washing powders remove stains made of protein by:

Hydrolysing the peptide bonds between the amino acids; [1 mark]

• The amino acids are then dissolved into the water / can be washed away: [1 mark]

[Total: 2 marks]

b) The biological washing powder manufacturers claim can be evaluated as:

Any four from the following:

It is more effective with all stains: [1 mark] It is most effective with ketchup/lasagna OR the greatest difference between washing powders is seen with ketchup / lasagna stains; [1 mark]

However, there is little improvement (compared to the other washing powder) with lemon sorbet and coffee: [1 mark]

Only tested on 5 different types of stains/ more types of stains should be tested

[1 mark]

No repeats/only compared against one type of washing powder, [1 mark

No standard deviations calculated/statistical test carried out so we don’t know the

significance of the data; [1 mark