▶️ Answer/Explanation
(a)(i) An explanation that makes reference to two of the following:
- (Flask B) as (mouthpiece) connected to long tube in flask B / (mouthpiece) connected to flask A is shorter (1)
- (Flask B) tube (from mouthpiece) in limewater / tube in liquid in flask B / causes bubbles (in limewater) in B / not in liquid / draws air in flask A (1)
- cannot inhale in flask B as limewater would be sucked in / would get mouthful of liquid / Flask A for inhalation as no liquid drawn up (1)
(2 marks)
(a)(ii) An explanation that makes reference to two of the following:
- (Limewater) in flask A stays clear / no change / less cloudy / goes cloudy slowly (1)
- (Limewater in) flask B goes (more) cloudy / milky / cloudy quicker (1)
- as less carbon dioxide \( \text{(CO}_2\text{)} \) in inhaled / atmospheric air / (more) carbon dioxide in exhaled (1)
- due to respiration (1)
(2 marks)
(a)(iii) • Sodium hydrogencarbonate / sodium bicarbonate (solution) / hydrogencarbonate / bicarbonate indicator (1)
(1 mark)
(b) An answer that makes reference to four of the following:
- diaphragm contracts (1)
- diaphragm flattens / moves down (1)
- (external) intercostal muscles contract (1)
- rib cage raised / moves out (1)
- volume (of chest cavity / thorax) increases (1)
- pressure in (chest cavity / thorax) decreases / reduces (1)
- air drawn into lungs / lungs inflate (1)
(4 marks)
▶️ Answer/Explanation
(a)(i) A (anther)
B is not the answer as it is the filament
C is not the answer as it is the stigma
D is not the answer as it is the style
(a)(ii) B (petal)
A is not the answer as it is the leaf
C is not the answer as it is the stem
D is not the answer as it is the style
(a)(iii) D (S, stigma)
A is not the answer as they do not germinate on P (anther)
B is not the answer as they do not germinate on Q (petal)
C is not the answer as they do not germinate on R (stem)
(b) An answer that makes reference to the following:
• P / anthers exposed / hanging out / outside / eq (1)
• S / stigma feathery / exposed / hanging out / longer / outside / eq (1)
• Q / petals smaller / absent / green / not coloured / not scented / eq (1)
(c)(i) One natural method, e.g.:
• runners / eq
allow corms / bulbs / rhizomes / tubers
(c)(ii) One artificial method, e.g.:
• cuttings / eq
allow grafting / layering / micropropagation / tissue culture
(c)(iii) An answer that makes reference to two of the following:
• no / (less) genetic variation / a clone / eq (1)
• maintain phenotype / colour / flavour / desired characteristic / same characteristics / eq (1)
• faster / eq (1)
• seeds not viable / produce rare plants / eq (1)
▶️ Answer/Explanation
(a) Carbon (cycle) (1)
(b)(i) The only correct answer is A (combustion)
B is not the answer as W is not decomposition
C is not the answer as W is not feeding
D is not the answer as W is not respiration
(b)(ii) The only correct answer is D (respiration)
A is not the answer as X is not combustion
B is not the answer as X is not decomposition
C is not the answer as X is not feeding
(c) bacteria / fungi / allow correct genus and species names (1)
(d) A description that makes reference to six of the following points:
• C Use different pH of organic material / add acid / alkali / add buffers / etc. (1)
• O Use the same organic material / plant / age / species / type / mass / volume of organic material (same state of decay) (1)
• R Repeat (at each different pH) (1)
• M1 Measure change / loss in mass of organic material (initial mass – final mass) / volume of carbon dioxide released / change in hydrogen-carbonate indicator / change in limewater / etc. (1)
• M2 After a stated time period (e.g., 1 hour+) / measure time taken for same mass to decompose (1)
• S1 Keep the same temperature / oxygen levels / etc. (1)
• S2 Keep the same water / mineral ions / humidity / volume of each acid/alkali/buffer / same bacteria/fungi/decomposer added / etc. (allow same number of bacteria/decomposers) (1)
Example full-sentence answer structure:
I would set up several containers with the same type, mass, and state of decay of organic material. I would adjust the pH in each container to different values using buffers or acids/alkalis, while keeping other factors like temperature, oxygen availability, and humidity the same. I would then measure the loss in mass of the organic material after a fixed period, such as one week, to determine the rate of decomposition. This experiment would be repeated at each pH level to ensure reliability.
▶️ Answer/Explanation
(a)(i)
Number of mothers aged ≤19 who smoked = 356
Total mothers aged ≤19 = \(1331 + 356 = 1687\)
Percentage = \( \frac{356}{1687} \times 100 \)
\( \approx 21.1\% \)
Answer: 21.1% (allow 21%)
(a)(ii)
Total non-smokers = \(1331 + 11243 + 24099 + 28695 + 16537 + 3242 = 85147\)
Total smokers = \(356 + 1677 + 2211 + 1847 + 934 + 181 = 7206\)
Ratio (non-smokers : smokers) = \( \frac{85147}{7206} : 1 \)
\( \approx 11.82 : 1 \)
Nearest whole number ratio = \(12 : 1\)
Answer: \(12 : 1\)
(b)
An answer that makes reference to points such as:
- Yes, smoking is important / correlated:
- At every age group, the percentage of low birth mass babies is higher for smokers than non-smokers.
- The difference is especially large in older age groups (e.g., 35–39: 10.5% vs 21.1%).
- The study involves large numbers, giving statistical weight.
- No, it is not the sole/main factor / correlation ≠ causation:
- There is also a clear age effect: for non-smokers, low birth mass % is higher in very young (≤19: 11.5%) and older mothers (≥40: 12.3%).
- The effect of smoking appears greater in older mothers, suggesting an interaction; older mothers may have smoked for longer.
- Other factors not recorded could be responsible (confounding variables): mother’s mass/weight, healthcare, diet, alcohol/drug use, prenatal care, genetics, premature birth.
- No information on frequency/duration of smoking.
- Biological knowledge: smoking reduces oxygen supply to fetus (via carbon monoxide binding haemoglobin, vasoconstriction), impairs placental function, but other factors also affect fetal growth.
- Conclusion: The data shows a strong association, but the student’s conclusion that smoking is the main cause is an oversimplification. Other factors, especially age and unmeasured variables, also play significant roles.
▶️ Answer/Explanation
(a) An explanation that makes reference to two of the following:
- anaerobic respiration (1)
- (by) bacteria / named bacteria (e.g., Lactobacillus) (1)
- produces lactic acid / eq (1)
(b) • temperature / volume / mass of milk / lactose content of milk / type of milk / eq (1)
(c)(i) A graph that includes:
- scales linear and at least half page and axes the correct way around (time on \(x\)-axis) (1)
- (time in) minutes and acidity % labelled (1)
- straight lines joining points (1)
- points correctly plotted (1)
- key to identify normal and low oxygen (1)
(c)(ii) An explanation that makes reference to the following:
- reduced oxygen (more) anaerobic respiration (of milk) / less aerobic respiration / eq (1)
- acidity increases faster / sooner / more rapidly / eq (1)
Marking note for (c)(ii): Allow converse for more oxygen (i.e., normal oxygen level has more aerobic respiration, so acidity increases more slowly).
▶️ Answer/Explanation
(a)
A: oesophagus / gullet (1)
B: stomach (1)
C: small intestine / ileum / duodenum / jejunum (1)
D: large intestine / colon (1)
(b) An explanation that makes reference to three of the following:
• (plants contain) cellulose (1)
• (cellulose) digested by cellulase / enzyme (1)
• into glucose (1)
• energy released / respiration (1)
(c)(i)
• humans do not digest cellulose / do not eat only plant material / omnivores / eat fewer plants / vegetables (1)
(c)(ii) An answer that makes reference to two of the following:
• removes useful bacteria / fewer / no useful bacteria (1)
• reduces competition (1)
• pathogenic bacteria increase / survive / multiply / grow / more harmful bacteria (1)
▶️ Answer/Explanation
(a)(i) D (oak tree)
A is not correct as it is not the producer
B is not correct as it is not the producer
C is not correct as it is not the producer
(a)(ii) A (blackbird)
B is not correct as it is not a secondary and tertiary consumer
C is not correct as it is not a secondary and tertiary consumer
D is not correct as it is not a secondary and tertiary consumer
(b)(i) An explanation that makes reference to the following:
• some light / colours / wavelengths are reflected (1)
• light falls on flowers / not on leaves / some does not fall on chloroplasts / chlorophyll (1)
Ignore: shade. Allow: not enough chloroplasts.
(b)(ii)
• Producer to primary consumer: \( \frac{1.4 \times 10^4}{8.7 \times 10^5} \times 100 = 1.61\% \) (1) (allow 1.6%)
• Primary to secondary consumer: \( \frac{1.6 \times 10^3}{1.4 \times 10^4} \times 100 = 11.4\% \) (1) (allow 11%, 11.43%)
OR calculation of energy lost:
• Producer to primary: \(100 – 1.61 = 98.4\%\) lost (1)
• Primary to secondary: \(100 – 11.4 = 88.6\%\) lost (1)
• Conclusion: The student is incorrect; the transfer from primary to secondary consumer is more efficient (as 11.4% > 1.61%).
(c)(i) • involuntary / automatic / does not involve the brain / spontaneous / without thinking / unconscious (1)
(c)(ii) • protects from predators / only exposes hard shell (1)
Ignore: danger / harm / injury.
(c)(iii) An answer that makes reference to four of the following:
• (gene) mutation / mutated gene (1)
• variation (in rolling behaviour) (1)
• woodlice that roll up survive / are not eaten (1) (allow converse)
• (survivors) reproduce (1) (allow converse)
• pass on alleles / genes (for rolling behaviour) (1)
Do not accept: just “pass on mutation / behaviour”.
▶️ Answer/Explanation
(a)
0.04% = 0.04 in 100
\(1\,000\,000 \div 100 = 10\,000\)
\(10\,000 \times 0.04 = 400\)
concentration = 400 ppm (2 marks)
Allow 1 mark for correct calculation of 10,000.
(b)(i)
An answer that makes reference to the following:
• (Increasing CO2) increases (relative) rate of photosynthesis (1)
• (Begins to) level off / reaches maximum (at 0.10% at approx. 1.12) / rate of increase steepest up to 0.06% / eq (1)
(b)(ii)
An answer that makes reference to two of the following:
• Steepest increase / most effect at 35°C / higher temperatures / eq (1)
• Increasing CO2 increases (relative) rate of photosynthesis at all temperatures (1)
• At CO2 of 0.03%, temperature is not the limiting factor / CO2 is limiting factor so increasing the temperature has little effect (1)
(b)(iii)
An explanation that makes reference to three of the following:
• Increasing temperature increases (relative) rate of photosynthesis (1)
• As more (kinetic) energy (supplied to molecules) / eq (1)
• More (frequent) collisions / faster collisions (between substrate and enzyme molecules) / more enzyme-substrate complexes formed / eq (1)
• Temperature becomes limiting factor at 5°C / increasing CO2 has less effect on rate / eq (1)
(c)(i)
An explanation that makes reference to one pair of the following:
• Nitrate (1) for / amino acids / proteins / stunted growth / eq (1)
OR
• Magnesium (1) for chlorophyll / yellow leaves / chlorosis / eq (1)
OR
• Other correct mineral (e.g., potassium, phosphate) (1) with correct effect (e.g., poor root growth, poor flowering) (1)
(c)(ii)
An explanation that makes reference to two of the following:
• (Increasing) light (intensity) (1) provides energy for / required for photosynthesis / absorbed / trapped / used by chloroplasts / chlorophyll / stomata open more / eq (1)
OR
• Changing wavelength / colour of light (1) some not absorbed / affect photosynthesis (1)
OR
• (Availability of) water (1) as reactant / substrate / used in photosynthesis (1)
Allow other valid factors such as pollutants or oxygen concentration.
▶️ Answer/Explanation
(a) • only expressed / seen in phenotype of homozygous / requires two / both (copies) to be expressed in phenotype / only seen / expressed / shown if no dominant allele present / not expressed if dominant allele present / eq (1)
(b)(i) Correct genetic diagram:
- Parents: Aa and Aa (1)
- Gametes: A and a from each parent (1)
- Offspring genotypes: AA, Aa, Aa, aa (1)
- Offspring phenotypes: 3 no symptoms : 1 alkaptonuria (1)
(b)(ii) probability = \(0.375\) / \(37.5\%\) / \(3/8\) (1)
(c)(i) • did not receive the drug / no treatment / eq (1)
(c)(ii) An evaluation that makes reference to five of the following points: (5)
- Yes (the drug is effective) because:
- control group so valid study /eq (1)
- drug group showed improvement/reduced symptoms / eq (1)
- quicker to stand up (1.33 s vs 0.54 s decrease) / eq (1)
- improved distance walked (51.5 m vs 6.7 m increase) / eq (1)
- No (caution/reservations) because:
- small group size / should be tested on more people / repeat study / eq (1)
- not all finished study (16/20 vs 17/20) / eq (1)
- adverse / side effects (2 patients in drug group) / eq (1)
- one died in drug group /eq (1)
- no information on age / mass / sex / other health conditions / activity / eq (1)
(d) An answer that makes reference to two of the following points: (2)
- patients may not know what foods contain these (amino acids)/eq (1)
- (tyrosine and phenylalanine are) present in many / most foods / most proteins /eq (1)
- proteins (that contain them) are required for growth / repair / eq (1)
▶️ Answer/Explanation
(a) C (it is specific)
A is not correct because biological control is often longer-lasting, not short.
B is not correct because bioaccumulation is a disadvantage of some chemical pesticides.
D is not correct because biological control is generally slower acting than chemical control.
(b)(i) An answer that includes the following:
- sucrose / sugars (1)
- amino acids (1)
Additional guidance: ignore water, reject starch/glucose. Allow named amino acid.
(b)(ii) An explanation that makes reference to four of the following:
- less sucrose / sugars transported to storage organs / fruits / grains / tubers (1)
- less amino acids for protein synthesis / growth (1)
- less energy (ATP) from respiration for growth / active transport (1)
- less material for making new plant tissue (e.g., leaves, roots) (1)
- weakened plant more susceptible to disease (1)
- aphids may spread plant viruses (1)
Note: The answer must logically link aphid feeding (removing phloem contents) to reduced plant growth or storage, leading to lower crop yield.
(c) Discussion that includes the following points:
Support for the conclusion:
- From the graph, hoverflies eat/consume more aphids than silverflies at all three temperatures. (1)
- Therefore, fewer hoverflies might be needed to control an aphid population. (1)
- The difference is greatest (approx. ×3) at 12°C, and still significant (approx. ×1.9) at 18°C. (1)
- Both species consume more aphids at higher temperatures. (1)
Limitations / Points against being fully conclusive:
- The method used only one larva per container – should use more larvae / not repeated enough for reliable mean. (1)
- It was a laboratory experiment, not a natural habitat / field study – conditions are controlled and simplified. (1)
- Only two species (hoverfly and silverfly) were compared – other potential biological control agents exist. (1)
- Temperature range tested (12–18°C) may not represent all seasonal field conditions. (1)
A balanced answer would reference both the supporting data and the methodological limitations to ‘discuss’ the conclusion.