▶️ Answer/Explanation
(a)(i) B (cell wall)
A is incorrect because it is not the cell membrane.
C is incorrect because it is not mitochondria.
D is incorrect because it is not the nucleus.
(a)(ii) D (starch)
A is incorrect because it is not chlorophyll.
B is incorrect because it is not glucose.
C is incorrect because it is not glycogen.
(b)(i) An answer that makes reference to the following points:
- A: (chloroplasts absorb light) for photosynthesis / absorb light energy to make carbohydrate / eq
- B: (nucleus) controls protein synthesis / contains DNA / contains genes / controls cell / eq
- C: (vacuole) contains cell sap eq
- D: (cytoplasm) where chemical reactions occur
Additional guidance: Allow starch / glucose / sugar for A; allow maintains turgor / stores water / salts / pigments / toxins for C; allow where protein synthesis occurs / respiration occurs / medium for reactions for D.
(b)(ii) An answer that makes reference to two of the following points:
- contains chloroplasts to absorb light / for photosynthesis eq
- long / arranged in a vertical plane / large surface area / rectangular shape, to absorb most light / eq
- large vacuole to store water
▶️ Answer/Explanation
(a) C (plasmid)
A is incorrect because it is not the cell wall
B is incorrect because it is not the nucleoid
D is incorrect because it is not RNA
(b)
The hormone called insulin is needed to control the blood glucose levels in humans.
Bacteria have been genetically modified to produce this hormone.
The fermenter is cleaned with steam / hot water before adding a nutrient broth that contains the genetically modified bacteria.
This cleaning provides aseptic conditions that prevent contamination / competition from other bacteria.
Paddles are used to mix / stir / agitate the contents.
A gas called oxygen / \(O_2\) is bubbled into the fermenter.
The temperature is controlled by using a cooling jacket.
Acceptable alternatives for blank 2: disinfectant, bleach, sterilising fluid, alcohol, ethanol.
Acceptable alternatives for blank 3: infection.
▶️ Answer/Explanation
(a)(i) D (trachea)
A is incorrect because it is not the bronchiole
B is incorrect because it is not the bronchus
C is incorrect because it is not the oesophagus
(a)(ii) B (pulmonary artery)
A is incorrect because it is not the aorta
C is incorrect because it is not the pulmonary vein
D is incorrect because it is not the vena cava
(a)(iii) A (contract, contract)
B is incorrect because the external intercostals do not relax
C is incorrect because the diaphragm does not relax
D is incorrect because the diaphragm and the intercostals do not relax
(b) An answer that makes reference to four of the following points:
• more blood to muscles / less blood to intestine (during exercise) / eq
• supply oxygen / oxygenated blood / glucose
• respiration
• energy / ATP
• muscle contraction
• less absorption of food / eq, in intestine when running /
Example full answer: When the horse runs, a much greater percentage of its total blood flow is directed to the leg muscles (increasing from 15% to 82%) to supply oxygen and glucose for aerobic respiration, which releases energy (ATP) for muscle contraction. Conversely, blood flow to the intestine decreases sharply (from 30% to 3%) because processes like digestion and absorption of food are less critical during intense physical activity. This redistribution ensures that the working muscles receive the oxygen and nutrients they need.
(c) An explanation that makes reference to two of the following points:
• (supply (more)) oxygen / there was a shortage of oxygen
• breakdown / remove lactic acid
• repay oxygen debt
• anaerobic respiration had occurred
Example full answer: The horse continues to breathe faster and deeply after running to repay an oxygen debt. During intense exercise, some muscles respire anaerobically, producing lactic acid. The continued high rate of breathing supplies extra oxygen to break down this lactic acid and to fully oxidise the remaining respiratory substrates.
▶️ Answer/Explanation
(a) An answer that makes reference to the following points:
• Arrows in correct direction (e.g., plants → caterpillars → mice → owls; plants → mice).
• Food web includes all four organisms in correct feeding relationships.
Example web: Plants have arrows to mice and caterpillars. Caterpillars have an arrow to mice. Mice have an arrow to owls.
(b) • Primary consumer / 1° consumer
(c)(i) • \(3 \times 10^3 = 3000\) per \(\text{km}^2\)
• \(3000 \times 5 = 15000\)
Answer: \(15000\) or \(1.5 \times 10^4\) mice.
(c)(ii) An answer that makes reference to three of the following points:
• More food / plants / caterpillars / other sources of food available.
• Warmer weather.
• Fewer other predators / owls ate other species.
• Less disease / infection.
• Higher birth rate than death rate.
(c)(iii) An answer that makes reference to two of the following points:
• Owls feed on other prey (not just mice).
• Insufficient food / energy to maintain more owls (carrying capacity reached).
• Owls have no (or few) predators.
• Birth rate ≈ death rate.
• Owls produce few offspring (so population changes slowly).
(c)(iv) An answer that makes reference to three of the following points:
• Use a trap / use filming / use a sample area / use a quadrat.
• Random sampling.
• Repeat.
• Count number of mice / faeces (in sample area).
• Calculate average.
• Multiply up to total area.
▶️ Answer/Explanation
(a)(i) An explanation that makes reference to three of the following points:
• oxygen
• glucose
• respiration
• energy / ATP
Example answer: The blood contains glucose and oxygen. These are used by the fetus’s cells in respiration to release energy in the form of ATP. This ATP provides the energy required for active transport processes to occur.
(a)(ii) An explanation that makes reference to two of the following points:
• antibodies (from mother)
• (bind to) antigens
• to kill bacteria / pathogen / virus eq
Example answer: Antibodies from the mother’s blood cross the placenta. These antibodies bind to antigens on pathogens, marking them for destruction or neutralizing them, which helps protect the fetus from infection.
(b) An answer that makes reference to two of the following points:
• fetus is female / a girl
• cells contain 46 chromosomes / 23 pairs / has a diploid number / has two sets of chromosomes / normal number of chromosomes / eq
• chromosomes have different lengths / sizes / shapes
Example answer: 1. The fetus is female because the sex chromosomes are XX. 2. The cell has the normal diploid number of 46 chromosomes (23 pairs).
(c)(i) An answer that makes reference to four of the following points:
• calcium for bone / teeth growth / bone / teeth development / prevent rickets
• protein to grow / for enzymes / antibodies / eq
• iron for haemoglobin / red blood cells / prevent anaemia
• vitamin D for bone growth / bone development / calcium absorption / strong bones
• more energy as baby is heavy / mother becomes heavy / more energy for fetal development / to carry baby / eq
Example answer: Extra calcium and vitamin D are required for the development of the fetus’s bones and teeth. Additional iron is needed to make haemoglobin for the increased blood volume and to prevent anaemia. More protein is required for the growth of fetal tissues and the production of enzymes and antibodies. Increased energy is needed as the mother’s body works harder and carries extra weight.
(c)(ii)
• \(9.0 \text{ mg} = 50\%\) more
• \(100\% = 9.0 \times 2 = 18 \text{ mg}\)
• Total needed \(= 18 + 9 = 27 \text{ mg}\)
Award full marks for correct numerical answer without working.
Final Answer: \(27 \text{ mg}\)
▶️ Answer/Explanation
(a) An explanation that makes reference to two of the following points:
• As distance from the city centre increases, the percentage area covered by lichen increases.
• There are more cars/pollution/sulfur dioxide in the city centre, which inhibits lichen growth.
Allow converse statements (e.g., lichen coverage decreases closer to the city centre).
(b) An answer that makes reference to three of the following points:
• Measure the area covered by lichen. Allow using a grid/quadrat to count squares with lichen.
• Measure the total area of the stone wall.
• Divide the lichen-covered area by the total area and multiply by \(100\) to get the percentage.
• Repeat the measurements in different places on the wall to find a mean.
(c) An answer that makes reference to six of the following points:
• C (Change): Expose one set of germinating seeds to sulfur dioxide (\(SO_2\)) from sodium metabisulphite and another set to air without \(SO_2\) (or use different concentrations of \(SO_2\)).
• O (Organisms): Use the same species/type/age/variety of seeds.
• R (Repeat): Use a large number of seeds/repeat the experiment.
• M1 (Measurement 1): Measure the temperature change.
• M2 (Measurement 2): Use a thermometer.
• S1 (Same 1): Use a thermos flask (or insulated container) to contain the seeds and prevent heat loss.
• S2 (Same 2): Control other variables (e.g., same moisture, oxygen, starting temperature, light, time, disinfect seeds).
Answer must be in full sentences and include experimental details to access the marks.
▶️ Answer/Explanation
(a) An explanation that makes reference to the following points:
- Amylase digests/catalyzes the breakdown of starch into maltose / glucose.
- These are reducing sugars, so the Benedict’s test will turn from blue to a red / green / yellow / orange precipitate.
(b) Rewritten method should include reference to at least four of the following control variables (1 mark each, max 4):
- Use the same volume and concentration of amylase solution.
- Use the same mass / size / volume / piece of bread.
- Use the same volume of water poured onto the bread.
- Allow the same amount of time for digestion before collecting the solution for testing.
- Use the same volume / concentration of Benedict’s reagent.
- Heat the Benedict’s test tubes for the same length of time and at the same temperature (e.g., in a water bath at \(80^\circ C\) for 2 minutes).
- Test a specific, stated range of temperatures (e.g., \(20^\circ C, 30^\circ C, 40^\circ C, 50^\circ C, 60^\circ C\)).
- Repeat each temperature and calculate a mean result.
(c) An answer that makes reference to four of the following points:
- Initially, as temperature increases, the rate of digestion increases.
- This is because particles (enzyme and substrate) have more kinetic energy, move faster, and collide more frequently.
- This continues until the optimum temperature is reached, where the rate is highest.
- Above the optimum temperature, the rate decreases rapidly.
- At high temperatures, the enzyme (amylase) denatures – the active site changes shape and the substrate (starch) can no longer bind.
- Therefore, the prediction is incorrect because the rate does not keep increasing indefinitely; it peaks and then falls (implied in the points above).
▶️ Answer/Explanation
(a) A correct line graph should show:
• Linear scales on both axes, covering at least half the grid.
• Axes plotted the correct way round (Year on x-axis, Percentage on y-axis).
• Straight lines joining each consecutive data point for both e-cigarettes and normal cigarettes.
• Axes labelled ‘Year’ and ‘Percentage of students’.
• All points plotted accurately (within one small square of the correct position).
• A key or labelled lines to distinguish between ‘e-cigarettes’ and ‘normal cigarettes’.
(b) A description that makes reference to two of the following points:
• E-cigarette use increased (from 2011) up to 2015 then decreased / decreased in 2016.
• Smoking normal cigarettes decreased (from 2011 to 2016).
• At the start, e-cigarette use was lower than smoking / significantly low; by the end, e-cigarette use was higher than smoking / significantly high.
(c)
Method 1:
• Difference in percentage: \(15.8 – 8.0 = 7.8\%\)
• Change in number: \(\frac{7.8}{100} \times 60,000 = 4680\) students
OR Method 2:
• Number in 2011: \(\frac{15.8}{100} \times 60,000 = 9480\)
• Number in 2016: \(\frac{8.0}{100} \times 60,000 = 4800\)
• Change: \(9480 – 4800 = 4680\) students (2)
Award full marks for correct numerical answer (4680) without working.
(d)(i) An explanation that makes reference to four of the following points:
• Less tar.
• Fewer carcinogens / less risk of cancer.
• Less risk of emphysema / lung disease / damage to alveoli / chronic bronchitis / damage to cilia.
• Less carbon monoxide.
• Less risk of heart disease / strokes.
• Less risk of addiction / can control nicotine levels.
(d)(ii) An answer that makes reference to two of the following points:
• Non-smokers may start using e-cigarettes.
• E-cigarettes may lead to taking up smoking.
• E-cigarettes are addictive as they contain nicotine.
• Nicotine can increase risk of blood clots / increase blood pressure.
• E-cigarettes may also be harmful / damage lungs / long-term risks not yet known.
▶️ Answer/Explanation
(a)(i) • cleft chin or not / appearance of chin / eq
(a)(ii) An answer that makes reference to one of the following points: (section of) DNA / eq that codes for cleft chin characteristic / protein / trait / eq
(a)(iii) • (different) version(s) of the (cleft chin) gene / alternative forms of the gene
(b)(i) An answer that makes reference to the following points:
• both parents \( Nn \)
• gametes produced \( N \) or \( n \) from each parent
• offspring genotypes shown \( NN\ Nn\ Nn\ nn \)
• offspring phenotypes shown 3 cleft 1 without cleft chin
Genetic Diagram (example):
Parents: \( Nn \) (Cleft) × \( Nn \) (Cleft)
Gametes: \( N, n \) × \( N, n \)
Offspring genotypes: \( NN, Nn, Nn, nn \)
Offspring phenotypes: 3 Cleft chin, 1 No cleft chin
(b)(ii) Probability of child being female = \( 0.5 \)
Probability of child not having cleft chin (\( nn \)) from \( Nn \) × \( Nn \) cross = \( 0.25 \)
Combined probability = \( 0.5 \times 0.25 = 0.125 \) / \( \frac{1}{8} \) / 12.5%
(b)(iii) An answer that makes reference to one of the following points:
• environment / diet / eq means different shaped chin
• mutation
(Accept: incomplete penetrance, interaction with other genes, epigenetic factors.)
(c) A description that makes reference to three of the following points:
• use crosses between different rats / test cross / pedigree analysis to predict outcomes / look at pedigree diagrams / family trees / family history
• if single gene, offspring show simple pattern / shows 3:1 ratios / look like one parent / eq
• single gene shows discontinuous variation / two or three phenotypes
• polygenic leads to continuous variation / intermediate expression / many different phenotypes / much more variation / three or more phenotypes
▶️ Answer/Explanation
(a) An explanation that makes reference to four of the following points:
- nitrates (for growth)
- for amino acids
- for protein
- magnesium for chlorophyll / chloroplasts
- so more photosynthesis
- more glucose
- phosphates used for ATP / DNA / eq
- potassium for control of water movement / eq
(b) An answer that makes reference to four of the following points:
- fertiliser leaches into river / washed into river / eq
- fertiliser would cause algal / plant growth / algal bloom / eutrophication
- dead algae are decomposed / broken down by bacteria / decomposers
- (bacterial) respiration would reduce oxygen
- means were calculated / readings repeated so experiment is reliable / valid
- measurements taken at same time of year / in April (so are valid)
- direction of river is past farm
- reduced oxygen could be due to other factors / sources of fertiliser from other fields
(c) • manure / faeces / dung / compost / seaweed / bone / blood / animal wastes / eq