Mark Scheme

Section A — Structured Questions

Question 1

(a) A: cell wall
D: nucleus
(1 mark each = 2 marks)

Accept: A: cellulose wall
Reject: A: membrane alone

(b) Any two from:

• plant cells have a nucleus / bacterial cells do not have a nucleus
• plant cells have mitochondria / bacterial cells do not have mitochondria
• plant cells have chloroplasts / bacterial cells do not have chloroplasts
• plant cell DNA is in the nucleus / bacterial cell DNA is in the cytoplasm / forms a loop / is circular
• bacterial cells have a cell wall made of different material (not cellulose)
• bacterial cells are much smaller than plant cells
  (1 mark each = 2 marks)

Accept: bacterial cells have plasmids / plant cells do not

(c) 400 / ×400
(1 mark)

Accept: 10 × 40 = 400

(d) Correct working: 20 ÷ 0.05
Answer: 400 / ×400
(1 mark for working, 1 mark for answer = 2 marks)

Accept: conversion to same units shown (e.g., 20mm ÷ 0.05mm or 0.02mm ÷ 0.00005mm)

Question 2

(a) stomach
(1 mark)

(b) Any two from:

• absorbs water (from undigested food)
• absorbs minerals / ions
• forms faeces
• (temporary) storage of faeces
  (1 mark each = 2 marks)

Do not accept: "absorbs food" without qualification

(c) Any three from:

• has a large surface area
• due to villi / many folds
• villi have thin walls / one cell thick / short diffusion distance
• good blood supply / many capillaries (to maintain concentration gradient)
• microvilli increase surface area further
  (1 mark each, max 3 marks)

Accept: epithelium is thin

(d)(i) stomach
(1 mark)

(d)(ii) Any two from:

• to kill bacteria / pathogens (in food)
• provides optimum pH for (stomach) enzymes / pepsin
• (helps) denature proteins / break down food
  (1 mark each = 2 marks)

Accept: for enzymes to work

Question 3

(a) distance of lamp from pondweed / light intensity / distance of lamp
(1 mark)

Accept: position of lamp
Reject: light alone

(b) Any one from:

• temperature (of water)
• type of pondweed / same plant
• volume / concentration of water
• time period (one minute)
• carbon dioxide concentration
  (1 mark)

(c) As distance increases, number of bubbles decreases
(1 mark)

AND

Relationship is described (e.g., inverse / negative correlation / the further away the fewer bubbles)
(1 mark = 2 marks total)

Accept: as distance decreases, number of bubbles increases

(d) Greater distance = lower light intensity
(1 mark)

Lower light intensity = slower rate of photosynthesis / less photosynthesis
(1 mark = 2 marks total)

Accept: light is a limiting factor / less light energy available

(e) carbon dioxide + water → glucose + oxygen
(1 mark for reactants, 1 mark for products = 2 marks)

Accept: CO₂ + H₂O → C₆H₁₂O₆ + O₂

(f) (9 + 15) ÷ 2 = 12 / 12 bubbles
(1 mark)

Question 4

(a) P: intercostal muscles
Q: diaphragm
(1 mark each = 2 marks)

Accept: P: rib muscles

(b) Ribs: move up / upwards / outwards / up and out
Diaphragm: moves down / flattens / contracts
(1 mark each = 2 marks)

Reject: ribs expand

(c) Movement of ribs and diaphragm increases volume (of chest / thorax)
(1 mark)

This decreases pressure (in chest / lungs)
(1 mark)

Air moves in from higher to lower pressure / pressure difference causes air to enter
(1 mark = 3 marks total)

Accept: creates a vacuum

(d)(i) Oxygen is used (by the body)
(1 mark)

For (aerobic) respiration / to release energy
(1 mark = 2 marks total)

Accept: for cellular respiration

(d)(ii) Nitrogen is not used (by the body) / is inert / does not react
(1 mark)

Accept: nitrogen is not involved in any processes

Question 5

(a) grass
(1 mark)

(b) the Sun / sunlight / solar energy
(1 mark)

Reject: light alone without qualification

(c) (An organism that) eats / feeds on producers / plants
(1 mark)

First consumer in food chain / at the second trophic level
(1 mark = 2 marks total)

Accept: herbivore for first mark only

(d) Any two from:

• movement / muscle contraction
• heat / maintaining body temperature
• growth / repair
• reproduction
• excretion
• respiration (accept as process using energy)
• undigested food / egestion / faeces
  (1 mark each = 2 marks)

(e) Any three from:

• less energy available at higher trophic levels
• (because) energy is lost between trophic levels / at each stage
• energy lost as heat / through respiration / movement / excretion / undigested food
• less energy available to support fewer organisms
• smaller population can be supported
  (1 mark each, max 3 marks)

Accept: only 10% of energy is passed on

Question 6

(a) Plant was deficient in nitrates / lacking nitrates / not enough nitrates
(1 mark)

Could not make enough chlorophyll
(1 mark = 2 marks total)

Accept: nitrates needed for chlorophyll production

(b) To make proteins / amino acids
(1 mark)

For growth / making new cells
(1 mark = 2 marks total)

Accept: for making DNA / enzymes / chlorophyll

(c) Aphids feed on phloem (sap)
(1 mark)

Remove sugars / nutrients / products of photosynthesis / reduce plant growth
(1 mark = 2 marks total)

Accept: pierce plant tissue / suck sap

(d)(i) Using (natural) predators / parasites / living organisms
(1 mark)

To control pests / reduce pest numbers
(1 mark = 2 marks total)

Accept: specific example (e.g., using ladybirds to eat aphids)

(d)(ii) Any one from:

• does not harm other organisms / only affects target pest
• does not pollute environment / no chemical residue
• pests do not develop resistance
• may be longer lasting / self-perpetuating
• no bioaccumulation
  (1 mark)

Section B — Extended Response

Question 7

(a) Maintaining a constant internal environment
(1 mark)

Despite changes in external conditions
(1 mark = 2 marks total)

Accept: keeping conditions stable / regulation of internal conditions

(b) Any three from:

• sweat is produced by sweat glands
• sweat contains water
• water in sweat evaporates from skin surface
• evaporation requires heat / energy
• heat is taken from the body / skin
  (1 mark each, max 3 marks)

Accept: latent heat of vaporization

(c) Vasodilation means widening / dilation of blood vessels / arterioles (near skin surface)
(1 mark)

OR relaxation of muscles in vessel walls
(1 mark for definition)

More blood flows near the surface of the skin
(1 mark)

More heat is lost by radiation (from blood to environment)
(1 mark = 4 marks total)

Accept: increased blood flow to skin

(d) Level 3 (5–6 marks): A detailed and coherent explanation that covers all three bullet points. The answer explains clearly the role of insulin in lowering blood glucose, describes glucose conversion and storage, and explains consequences of system failure with reference to diabetes. Scientific terminology is used accurately throughout.

Level 2 (3–4 marks): A reasonable explanation that covers at least two bullet points with some detail. There may be some gaps in the explanation or limited use of scientific terminology. The link between insulin and glucose regulation is made but may lack full development.

Level 1 (1–2 marks): A basic answer that shows some understanding but is fragmented or only covers one bullet point. Limited use of scientific terminology. May contain errors or be unclear.

Indicative content:

• Blood glucose concentration rises after eating carbohydrates
• Detected by pancreas
• Pancreas secretes insulin (into blood)
• Insulin travels to liver / target organs
• Insulin causes glucose to be converted to glycogen
• Glycogen is stored in liver / muscles
• This reduces blood glucose concentration back to normal
• If system doesn't work properly: diabetes / blood glucose remains high
• Can cause damage to organs / kidneys / eyes / nerves / blood vessels
• Person may need insulin injections / need to control diet

Question 8

(a) Substrate: starch
Product: maltose / (reducing) sugar
(1 mark each = 2 marks)

Accept: product = glucose / carbohydrate

(b) As temperature increases (from 10°C to 40°C), time taken decreases
(1 mark)

Relationship described (e.g., inverse relationship / negative correlation / enzyme activity increases)
(1 mark = 2 marks total)

Accept: reaction gets faster

(c) Temperature is too high
(1 mark)

Enzyme is denatured / active site has changed shape / substrate no longer fits
(1 mark = 2 marks total)

Accept: enzyme has been destroyed
Reject: enzyme has died

(d) Level 3 (7–9 marks): A comprehensive and well-structured evaluation that addresses all four bullet points. The answer defines optimum temperature clearly, critically evaluates the data with reference to limitations (e.g., need for more data points, need for repeats, 40°C may not be true optimum), suggests specific improvements to the investigation, and explains the importance of enzyme activity in digestion with relevant examples. Scientific terminology is accurate and used appropriately throughout. The answer shows clear reasoning and draws a justified conclusion.

Level 2 (4–6 marks): A reasonable evaluation that addresses at least three bullet points with some detail. The answer may lack critical depth in evaluation or miss some key points. There is some use of scientific terminology but this may be inconsistent. The answer shows some logical structure but may lack full coherence.

Level 1 (1–3 marks): A limited answer that addresses one or two bullet points in a basic way. Little evaluation or critical thinking is shown. Scientific terminology is limited or used incorrectly. The answer may be poorly structured or lack coherence.

Indicative content:

Optimum temperature:

• Temperature at which enzyme works fastest / most active / highest rate of reaction
• Temperature at which active site and substrate have best complementary fit

Evaluation of data:

• Data shows 40°C is fastest in this range
• But only tested at 10°C intervals
• Optimum could be anywhere between 30°C and 50°C
• More data points needed (e.g., 35°C, 45°C)
• Only single readings taken / no repeats shown
• Results may not be reliable
• At 50°C enzyme denatured so optimum must be below this
• Evidence supports 40°C as best temperature tested but not necessarily true optimum

Improvements:

• Test at smaller intervals (e.g., every 5°C or 2°C around 40°C)
• Repeat experiment multiple times and calculate means
• Use same concentration of enzyme and starch
• Control temperature more precisely / use thermostatically controlled water bath
• Test more temperatures above 40°C (e.g., 42°C, 44°C, 46°C, 48°C)
• Measure volume of substrate more accurately
• Use a colorimeter instead of iodine test for more accurate results

Importance in digestion:

• Enzymes break down large food molecules into smaller molecules
• These can be absorbed into blood
• Amylase specifically breaks down starch into sugars in mouth and small intestine
• If body temperature too high or too low, digestion would be inefficient
• Protease breaks down proteins to amino acids
• Lipase breaks down fats to fatty acids and glycerol
• Enzymes must work at body temperature (37°C)
• Different enzymes work in different parts of digestive system at different pH values

Sample Answers with Examiner Commentary

Question 7(d) — Sample Answers

Grade A (high distinction) answer*

When blood glucose concentration becomes too high after eating a meal containing carbohydrates, the rise in glucose is detected by the pancreas. The pancreas responds by secreting the hormone insulin into the bloodstream. Insulin travels around the body in the blood until it reaches target organs, particularly the liver and muscles. Insulin causes cells in these organs to take up more glucose from the blood. In the liver and muscle cells, insulin triggers the conversion of glucose into glycogen, which is a storage molecule. The glycogen is stored in the liver and muscles. This process removes excess glucose from the blood and causes the blood glucose concentration to decrease back to the normal level of approximately 90 mg per 100 cm³.

If this control system did not work properly, the person would have diabetes. In diabetes, either the pancreas does not produce enough insulin (Type 1) or the body cells do not respond properly to insulin (Type 2). This means that blood glucose concentration remains too high after eating. Over time, high blood glucose can damage blood vessels and cause serious health problems including kidney damage, damage to the retina leading to blindness, nerve damage, and increased risk of heart disease. People with diabetes may need to inject insulin or take medication, monitor their blood glucose regularly, and control their diet by limiting sugar intake.

Mark: 6/6

Examiner commentary: This is an exemplary answer that addresses all three bullet points with clarity and precision. The candidate demonstrates excellent understanding of the role of insulin, clearly explains the conversion and storage of glucose as glycogen, and provides detailed consequences of system failure with specific medical conditions and complications. The answer is well-structured, uses accurate scientific terminology throughout (e.g., "secreting," "target organs," "glycogen"), and shows the ability to link concepts together coherently. Full marks awarded.

Grade C (pass) answer

When blood glucose gets too high, the pancreas makes insulin. Insulin is a hormone that goes into the blood. Insulin makes the glucose turn into glycogen. Glycogen is stored in the liver. This makes the blood glucose go back down to normal levels.

If this didn't work, the person would get diabetes. This means their blood sugar stays high. High blood sugar is bad for you and can damage your organs like your kidneys. People with diabetes have to be careful what they eat and some people have to inject insulin to control their blood sugar.

Mark: 3/6

Examiner commentary: This answer demonstrates basic understanding and gains marks for stating that the pancreas produces insulin, that insulin causes glucose to be converted to glycogen, that glycogen is stored in the liver, and that failure leads to diabetes with potential organ damage. However, the answer lacks detail and precision. The candidate does not explain how insulin works (e.g., traveling to target organs, causing cells to take up glucose), does not mention muscles as a storage site, and provides limited detail about consequences of diabetes. The answer would benefit from more scientific terminology and fuller explanations of mechanisms.

Grade E (near miss) answer

When you eat carbohydrates your blood sugar goes up. The body makes insulin to control this. Insulin breaks down the glucose so that it can be used by the body for energy. This means the blood sugar goes back to normal.

If the body couldn't control blood sugar it would be dangerous. The person might get diabetes which means they have too much sugar in their blood. They would need to take tablets or insulin injections.

Mark: 2/6

Examiner commentary: This answer shows limited understanding and contains a significant misconception: the candidate states that insulin "breaks down" glucose for energy, when actually insulin's role is to promote glucose storage as glycogen and uptake by cells, not breakdown for immediate energy release. The candidate correctly identifies that insulin is involved in control and that diabetes results from system failure, gaining minimal credit. However, there is no mention of the pancreas detecting the rise, no explanation of glucose being converted to glycogen for storage, and very limited detail about consequences of diabetes. To improve, the candidate needs to learn the specific mechanism of insulin action and distinguish between immediate energy use and storage of excess glucose.

Question 8(d) — Sample Answers

Grade A (high distinction) answer*

The optimum temperature is the temperature at which an enzyme has the highest rate of activity and works most efficiently. At the optimum temperature, the enzyme and substrate molecules have the most kinetic energy without the enzyme becoming denatured, so the maximum number of enzyme-substrate complexes form per unit time.

The data provides some support for the conclusion that 40°C is the optimum temperature for amylase. Within the range tested, 40°C gave the fastest breakdown of starch (2 minutes compared to 3 minutes at 30°C and 5 minutes at 20°C). At 50°C the enzyme appears to have been denatured as no starch breakdown occurred even after 10 minutes, suggesting the optimum must be below 50°C. However, there are significant limitations to this conclusion. Firstly, temperatures were only tested at 10°C intervals, so the true optimum could be anywhere between 30°C and 50°C – it might be 38°C or 42°C for example. Secondly, only single measurements were taken at each temperature with no repeats, so we cannot assess reliability or calculate mean values. The result at 40°C could be anomalous.

To improve the investigation, the student should test additional temperatures at smaller intervals, particularly between 35°C and 45°C, to pinpoint the optimum more precisely. Each temperature should be tested at least three times and mean values calculated to ensure reliability. The student should also ensure control variables are properly maintained, such as using the same concentrations of enzyme and starch solution, and the same pH. Using a thermostatically controlled water bath would ensure more precise temperature control. A more quantitative method of measuring the breakdown of starch, such as using a colorimeter to measure the intensity of the blue-black color when iodine is added, would provide more accurate data than simply observing when starch is "completely broken down."

Enzyme activity is crucial in digestion because enzymes break down large, insoluble food molecules into small, soluble molecules that can be absorbed through the small intestine wall into the bloodstream. Amylase breaks down starch into maltose in the mouth and small intestine. Protease enzymes break down proteins into amino acids in the stomach and small intestine, while lipase breaks down lipids into fatty acids and glycerol in the small intestine. These enzymes must work effectively at body temperature (approximately 37°C), which is why the body maintains a constant temperature through homeostasis. If enzymes did not function properly, food would not be digested efficiently and nutrients could not be absorbed, leading to malnutrition.

Mark: 9/9

Examiner commentary: This is an outstanding answer that fully addresses all four bullet points with sophistication and depth. The candidate provides a precise definition of optimum temperature with reference to enzyme-substrate complex formation. The evaluation is critical and balanced, acknowledging what the data shows while clearly identifying limitations (interval size, lack of repeats, possibility of anomalous results). Multiple specific and practical improvements are suggested with scientific justification. The explanation of enzyme importance in digestion is comprehensive, covering multiple enzyme types, the need for small soluble molecules, and links to absorption and homeostasis. The answer demonstrates excellent command of scientific terminology and principles throughout. Full marks awarded.

Grade C (pass) answer

The optimum temperature is the best temperature for an enzyme to work at. At this temperature the enzyme works fastest.

The data shows that 40°C is the optimum because this is where the starch was broken down quickest in only 2 minutes. At 50°C the enzyme stopped working because it got denatured, which means it got too hot and broke. This shows the optimum is definitely below 50°C. However, the student only tested every 10°C so the real optimum might not be exactly 40°C, it could be a bit higher or lower. They should test more temperatures like 35°C and 45°C to be more accurate.

To improve the investigation, the student should do more tests at each temperature to make sure the results are reliable. They could also test temperatures closer together to find the exact optimum. The temperature should be kept constant using a water bath.

Enzymes are important in digestion because they break down food. Amylase breaks down starch into sugar. Other enzymes break down proteins and fats. The enzymes need to work at body temperature which is 37°C. If enzymes didn't work, we couldn't digest our food properly and wouldn't get the nutrients we need.

Mark: 5/9

Examiner commentary: This answer demonstrates sound understanding and covers all four bullet points, but lacks the depth and precision required for top marks. The definition of optimum temperature is acceptable but simplistic. The evaluation correctly identifies that 40°C was fastest and recognizes the limitation of 10°C intervals, but doesn't discuss lack of repeats or reliability issues in depth. Improvements suggested are relevant (more temperatures, repeats) but lack detail about specific temperatures to test or more sophisticated methods. The importance of digestion section covers basic points but lacks specific detail about why small molecules are needed, where different enzymes work, or the role of homeostasis. More scientific terminology and fuller explanations would strengthen this answer to reach the higher mark band.

Grade E (near miss) answer

Optimum temperature is the best temperature. 40°C is the optimum because the starch broke down fastest at this temperature taking only 2 minutes. At 50°C the enzyme didn't work because the temperature was too hot.

The student could improve the experiment by testing more temperatures. They should also repeat it to make sure they got the right answer.

Enzymes are important because they digest food. Amylase digests starch. If we didn't have enzymes we couldn't break down our food. Enzymes work best at certain temperatures and if it's too hot they get denatured and stop working.

Mark: 3/9

Examiner commentary: This answer shows basic awareness but lacks development and detail throughout. The definition of optimum temperature is too vague ("best temperature" without explaining what "best" means in terms of reaction rate). The evaluation simply restates data without critical analysis – there is no discussion of data limitations beyond recognizing that more temperatures could be tested, and no specific suggestions about which temperatures or why. The improvements section is superficial with no detail about methods or controls. The digestion explanation is limited to basic statements without explaining why breakdown is necessary (i.e., to produce small, soluble molecules for absorption). To improve, the candidate needs to develop each point with more detail, use more precise scientific vocabulary, and demonstrate critical thinking rather than just describing what happened.