Cambridge IGCSE Co-ordinated Sciences 0654/42 is the May/June 2026 Paper 4 Theory (Extended), variant 2. It lasts 2 hours, is worth 120 marks and is sat by every Extended candidate. It had twelve compulsory questions: Questions 1 to 4 were biology, 5 to 8 chemistry and 9 to 12 physics, each block worth 40 marks. No question was worth more than 11 marks, so the paper rewards steady accuracy across all three sciences rather than one long answer. This guide goes through the paper question by question and shows what the official mark scheme gave marks for. The paper and its mark scheme are free on the Tutopiya Learning Portal.

For an overview of all six 0654 papers from this series, see IGCSE Co-ordinated Sciences 0654 May/June 2026 past papers: what came up and how it was marked.

0654/42 at a glance

Question	Topic	Marks	Main command word
1	Biology: leaf structure, testing for carbon dioxide, stomata density	11	Describe, calculate
2	Biology: blood glucose control and negative feedback	7	Describe, complete
3	Biology: selective breeding, antibiotics, bacterial cells, decomposition	11	Describe, explain
4	Biology: sexual reproduction, gametes, asexual reproduction	11	Complete, describe
5	Chemistry: nitrogen, diffusion, air, oxides of nitrogen, N₂ bonding	10	Describe, complete
6	Chemistry: transition elements, noble gases, metallic and ionic bonding	11	Describe, explain
7	Chemistry: rate of reaction with sodium thiosulfate, collision theory	11	Explain, identify
8	Chemistry: reactions of ethene, combustion of ethane, fractional distillation	8	State, draw
9	Physics: speed and velocity, a velocity-time graph, force and kinetic energy	10	Calculate
10	Physics: ultraviolet, longitudinal waves and ultrasound, a lens ray diagram	10	State, complete
11	Physics: resistance of wires, series and parallel resistors, electrical energy	9	Calculate
12	Physics: uranium-235, fission and fusion, the Moon, the Big Bang	11	State, calculate
	Total	120

Question-by-question walkthrough

Question 1: leaf structure and stomata (11 marks, biology)

A diagram showed cells in part of a leaf, with five labelled parts.

• Name cell C (1 mark): guard cell. “Stomata” was ignored.
• Pigment in part A (1 mark): chlorophyll. “Chloroplast” was ignored, because the question asked for the pigment.
• How layers D and E adapt the leaf for photosynthesis (4 marks, marked independently): for D, many air spaces, which allow efficient diffusion of gases (gas exchange). “Empty space” was ignored, but “air gaps” was accepted. For E, tightly packed cells with many chloroplasts (lots of chlorophyll) to absorb more light; or cells positioned near the surface of the leaf to receive more light. “Store” in place of “absorb” was ignored.
• Test for carbon dioxide (1 mark): bubble the gas through limewater. Hydrogencarbonate indicator was also accepted.
• Carbon dioxide compared with atmospheric air (2 marks): in leaf air spaces it is higher at night and lower in the day; in inspired air it is the same; in expired air it is higher. One mark for each correct pair.
• Stomata density (2 marks): the radius is half of 0.45 mm, so the area is 3.14 × 0.225² = 0.159 mm², and 10 ÷ 0.159 = 63 stomata per mm². The first mark is for the area. A final answer that rounds to 16 still earned 1 mark under error carried forward; for example, using the diameter in place of the radius gives about 16, so halve the diameter first.

Question 2: blood glucose control (7 marks, biology)

A flow diagram showed what happens when blood glucose is too high or too low.

• Hormone A (1 mark): insulin.
• Storage of glucose (2 marks): stored as glycogen in the liver. Remember that the mark scheme expects spellings that can’t be confused between glucagon and glycogen.
• Organ that secretes glucagon (1 mark): the pancreas.
• Negative feedback (3 marks, any three from four points): when blood glucose is too high, insulin is released; this makes glucose convert to glycogen, so the concentration falls back towards the set point. When it is too low, glucagon is released; this makes glycogen convert to glucose, so the concentration rises. The scheme also credited the idea of returning to the optimum.

Question 3: selective breeding, antibiotics and bacteria (11 marks, biology)

A table gave the number of eggs, egg mass and body mass for four types of chicken, A to D.

• Selective breeding (4 marks): the first mark needed both B and D: B lays the most eggs per month (27) and D lays the heaviest eggs (72 g). The other three marks came from: select chickens with the wanted features, breed them together, select offspring with the wanted features and repeat over many generations. “Selection of genes” was ignored, and breeding different species together was rejected.
• Why only the chicken with a bacterial infection gets antibiotics (2 marks): antibiotics kill only bacteria (they do not work on viruses), and unnecessary use can lead to antibiotic-resistant bacteria. “Fight bacteria” was ignored, and saying antibiotics work against all pathogens or viruses was rejected.
• Matching structures to functions (2 marks): cell wall maintains the shape of the cell, the plasmid contains extra genes, and the ribosome is the site of protein synthesis. All three correct scored 2; one or two correct scored 1. Extra lines were rejected.
• Process A in the carbon cycle (3 marks): decomposition; decomposers release carbon dioxide (and nutrients or ions) from dead matter; which producers use for photosynthesis, passing the carbon through food chains. “Respiration” and the idea of releasing energy were ignored.

Question 4: reproduction (11 marks, biology)

• Sentences on fertilisation (3 marks): fertilisation is the fusion of the nuclei of two gametes to form a zygote, and gametes with 23 chromosomes are haploid. “Chromosomes” for nuclei and “embryo” for zygote were ignored.
• How the egg cell is adapted (2 marks): an energy (nutrient) store in the cytoplasm, and a jelly coat that changes after fertilisation so only one sperm enters. A haploid nucleus was accepted as another valid point. “Cell wall” was rejected and “mitochondria for energy release” was ignored.
• Three differences between male and female gametes (3 marks): from the table, the female gamete is bigger and far more male gametes are produced. Then up to two more from your own knowledge: sperm are motile, have a flagellum, an acrosome and many mitochondria, and carry an X or a Y chromosome, while eggs have a jelly coat and an energy store. Copying numbers from the table without making a comparison was ignored.
• Describe asexual reproduction (2 marks): produces genetically identical offspring, from one parent. “Fusion of gametes” was rejected for the second point.
• A disadvantage in the wild (1 mark): there is no genetic variation, so the population cannot adapt to a change in the environment (for example, a disease could wipe out the whole population). “All more susceptible to disease” on its own was ignored.

Question 5: nitrogen (10 marks, chemistry)

• Particles in solid nitrogen (2 marks): arranged regularly and close together (a lattice), and they vibrate. “Fixed” or “don’t move” was ignored for the movement mark.
• Why hydrogen diffuses faster than nitrogen (2 marks): hydrogen has a smaller Mᵣ, so its molecules move faster. “Hydrogen is lighter”, “kinetic energy” and “diffuses faster” were ignored, so name the relative molecular mass and the speed of the molecules.
• Oxygen in clean, dry air (1 mark): 21%.
• How oxides of nitrogen form in engines (1 mark): nitrogen and oxygen from the air react because of the high temperature. Saying the nitrogen and oxygen come from the fuel was rejected.
• Catalytic converter equation (2 marks): 2CO + 2NO → 2CO₂ + N₂. One mark for the formulae and one for balancing. Correct equations with other oxides of nitrogen were accepted.
• Dot-and-cross diagram of N₂ (2 marks): one mark for three shared pairs between the two atoms and one for the rest of the structure (a non-bonding pair on each nitrogen). Any mixture of dots and crosses was accepted.

Question 6: the Periodic Table and bonding (11 marks, chemistry)

• Copper compared with potassium (2 marks): copper is more dense and less reactive. Ticking three boxes with two correct dropped to 1 mark, and four ticks scored 0.
• Why neon forms no compounds (2 marks): neon atoms have a full outer shell, so they do not need to lose, gain or share electrons. “Neon is in Group 0” was ignored.
• Where element X belongs (1 mark): section D, the non-metals at the top right. X does not conduct and forms an acidic oxide.
• Electronic configuration of magnesium (1 mark): 2,8,2 drawn on the shells.
• Why magnesium is malleable (1 mark): layers of ions can slide over each other. Any mention of “molecules” was rejected.
• Bonding in magnesium oxide (1 mark): ionic.
• What happens when magnesium bonds with oxygen (3 marks, any three): magnesium atoms lose electrons; oxygen atoms gain electrons; two electrons are transferred; oppositely charged ions (Mg²⁺ and O²⁻) form and attract. A correct dot-and-cross diagram was accepted.

Question 7: rate of reaction (11 marks, chemistry)

The disappearing-cross experiment: four concentrations of sodium thiosulfate, A to D, gave times of 42 s, 71 s, 124 s and 63 s.

• State symbol for sulfur (1 mark): (s).
• Fastest reaction (1 mark): A, the shortest time.
• Least concentrated solution (2 marks): C, because it took the longest time (slowest reaction).
• Why distilled water (1 mark): it contains fewer impurities than tap water. “Dirt” was ignored.
• Time at 40 °C for concentration C (1 mark): any time less than 124 s.
• Collision theory (3 marks, any three): the particles have more kinetic energy (move faster); more particles have the activation energy; collisions are more frequent (more collisions per second); and more collisions are successful. “Faster collisions” and plain “more collisions” were ignored.
• Sulfur dioxide as a pollutant (2 marks): produced from the combustion of fossil fuels that contain sulfur compounds. “Sulfuric” or “sulfurous” was ignored.

Question 8: reactions of ethene (8 marks, chemistry)

• Reactant A, making ethanol (1 mark): steam (water was accepted).
• Draw poly(ethene) (2 marks): one mark for a single bond between the carbon atoms (a double bond was rejected), one for the rest of the repeat unit with continuation bonds. Brackets and n were optional.
• Bromine colour change (1 mark): orange to colourless. “Goes clear” was ignored, because clear is not a colour.
• Complete combustion of ethane (2 marks): 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O, or C₂H₆ + 3½O₂ → 2CO₂ + 3H₂O. One mark for formulae, one for balancing. Watch the ethane/ethene spelling here.
• Chain length up the column (1 mark): it decreases from bottom to top.
• Use of naphtha (1 mark): chemical feedstock (making chemicals or plastics). Solvents and lighter fuel were also accepted, but “fuel” on its own was ignored.

Question 9: motion and forces (10 marks, physics)

• Speed and velocity (2 marks): speed has magnitude only (a scalar); velocity has magnitude and direction (a vector).
• Motion from 0 to 10 s (1 mark): non-constant acceleration; decreasing or non-uniform acceleration was accepted, because the curve gets less steep. “Increasing acceleration” was ignored.
• Acceleration from 15 to 30 s (2 marks): the gradient: (2.0 − 1.25) ÷ (30 − 15) = 0.050 m/s².
• Friction forces (3 marks): resultant force = ma = 1.2 × 5.0 = 6.0 N; friction = 10.5 − 6.0 = 4.5 N.
• Maximum velocity (2 marks): from E = ½mv², v² = 2 × 2.2 ÷ 1.2, so v = 1.9 m/s.

Question 10: waves and a lens (10 marks, physics)

• A use of ultraviolet (1 mark): detecting fake bank notes, security marking, sterilising, killing bacteria or sun tanning.
• A harmful effect (1 mark): damage to skin cells or eyes, or skin cancer. “Cancer” without saying where was ignored.
• Longitudinal wave sentence (2 marks): the direction of vibration is parallel to the direction of propagation. “Energy transfer” in the first gap was ignored.
• Lowest frequency of ultrasound with unit (1 mark): 20 000 Hz (20 kHz).
• Pressure at compressions and rarefactions (2 marks): pressure is higher at compressions because the particles are closer together (or lower at rarefactions because they are further apart). “Particles being denser” was ignored.
• Converging lens ray diagram (3 marks): one mark for each of two correct complete rays from the object to the image, and one for an inverted arrow drawn from the principal axis to where the rays cross. Arrowheads on the rays were ignored.

Question 11: resistance and circuits (9 marks, physics)

• Doubling the length of a wire (1 mark): the resistance doubles. “Increases” was ignored, so state the factor.
• Same length, twice the cross-sectional area (1 mark): half of 12.6 Ω, so 6.3 Ω.
• Total resistance (3 marks): a 40 Ω resistor in series with two 20 Ω resistors in parallel. The two 20 Ω resistors combine to 10 Ω, then 10 + 40 = 50 Ω. One mark for recalling a series or parallel formula, one for the 10 Ω, one for the total.
• Current at X (2 marks): the total current is 3.6 ÷ 50 = 0.072 A, which splits equally between the two 20 Ω branches, so the current at X is 0.036 A. Error carried forward applied from your total resistance.
• Energy supplied in 1 minute (2 marks): E = VIt = 3.6 × 0.18 × 60 = 39 J (38.88 J accepted). Remember to turn the minute into 60 seconds.

Question 12: nuclear physics and space (11 marks, physics)

• Protons and neutrons in uranium-235 (1 mark): 92 protons and 143 neutrons, both needed, in that order.
• Relative charge on the nucleus (1 mark): +92 (error carried forward from a wrong proton number).
• Nuclear fission (1 mark): a nucleus splits up.
• Background radiation from outside Earth (1 mark): cosmic rays, the Sun or exploding stars. “Sunlight” was ignored.
• Main reaction in the Sun (2 marks): nuclear fusion of hydrogen into helium. “Nuclear fission” was rejected.
• Radio wave travel time from the Moon (3 marks): use v = 2πr ÷ T with T = 27 × 24 × 60 × 60 s, giving r ≈ 3.8 × 10⁸ m. Then t = d ÷ v = 3.8 × 10⁸ ÷ 3.0 × 10⁸ = 1.3 s (1.27 s). The orbital speed is only there to find the distance.
• The Big Bang Theory (2 marks, any two): the Universe expanded from a single point of very high density and temperature; it is still expanding; it is about 13.8 billion years old (values from 13 to 14 billion accepted). “Pressure” was ignored.

Where the marks are on 0654/42

• Each science is worth exactly 40 marks. Biology is Questions 1 to 4, chemistry 5 to 8 and physics 9 to 12, so a weak science costs a third of the paper.
• Describe questions carried 28 of the 120 marks, the largest share: leaf layers in 1(c), negative feedback in 2(d), selective breeding in 3(a), gamete differences in 4(b)(ii), and electron transfer in 6(f)(ii) among them.
• Recall carried 25 marks: the “state”, “name” and “identify” parts, including the two tick-box questions in 6(a) and 6(c).
• Completing, drawing and writing equations carried 26 marks: sentence gaps, tables, the N₂ and magnesium diagrams, poly(ethene), two balanced equations and the ray diagram.
• Calculations carried 20 marks, mostly in physics (Questions 9, 11 and 12(d)), plus the stomata density in 1(e).
• Explain questions carried 20 marks, such as antibiotics in 3(b), decomposition in 3(c)(ii), diffusion in 5(b), neon in 6(b) and collision theory in 7(d)(ii).
• Suggest carried 1 mark: the time at 40 °C in 7(d)(i).
• The longest parts are 4 marks: 1(c) and 3(a). The 3-mark parts (2(d), 3(c)(ii), 4(a), 4(b)(ii), 6(f)(ii), 7(d)(ii), 9(c)(i), 10(c), 11(b)(i) and 12(d)) are where most marks are won or lost.

How to self-mark 0654/42 with the mark scheme

1. Learn the abbreviations first. A semicolon separates marking points, a slash shows alternatives, A means accept, R means reject, I means ignore, ORA means the reverse argument also scores, AVP means any other valid point, and ecf means error carried forward. An underlined word must appear in your answer, such as “limewater” in 1(d)(i) and “high temperatures” in 5(d)(i).
2. Check calculations by the final answer, then the working. A correct answer on the answer line scores full marks. If it is wrong, look for the method marks: the area in 1(e), the 6.0 N resultant force in 9(c)(i), and the 10 Ω combination in 11(b)(i).
3. Apply error carried forward. In 11(b)(ii), a wrong total resistance from 11(b)(i) used correctly still earns both marks.
4. Mark equations in two parts. In 5(d)(ii) and 8(b), one mark is for the formulae and one for balancing; multiples and fractions are fine.
5. Apply the list and tick-box rules. Extra ticks in 6(a) cost marks, and extra lines in 3(c)(i) were rejected.
6. Read the ignore notes. “More collisions” in 7(d)(ii), “hydrogen is lighter” in 5(b) and “increases” in 11(a)(i) all scored nothing because they were too vague.
7. Log each lost mark by science (biology, chemistry or physics) and by type: missing knowledge, a vague answer, or a calculation slip. Revise the weakest science first.

Sit 0654/42 as a timed mock

The paper allows 120 minutes for 120 marks, one minute per mark. A workable plan:

Block	Marks	Time
Question 1	11	11 minutes
Question 2	7	6 minutes
Question 3	11	11 minutes
Question 4	11	11 minutes
Question 5	10	9 minutes
Question 6	11	10 minutes
Question 7	11	10 minutes
Question 8	8	7 minutes
Question 9	10	10 minutes
Question 10	10	9 minutes
Question 11	9	9 minutes
Question 12	11	11 minutes
Check, especially units and equations	–	6 minutes

Question 12(d) has two steps (the orbit radius, then the travel time), so keep some of your checking time for it.

Other May/June 2026 0654 papers

• 0654 Paper 12 (Core Multiple Choice)
• 0654 Paper 22 (Extended Multiple Choice)
• 0654 Paper 32 (Core Theory)
• 0654 Paper 52 (Practical Test)
• 0654 Paper 62 (Alternative to Practical)

Practise and download

• Download 0654/42 and its mark scheme on the Learning Portal →
• All 0654 May/June 2026 papers: overview and marking patterns
• Try a free IGCSE Co-ordinated Sciences quiz

Need help with a 0654 topic? Book a free trial lesson with an IGCSE Co-ordinated Sciences tutor →

Frequently asked questions

What topics were on 0654 Paper 42 May/June 2026? +

Twelve questions, four per science. Biology: leaf structure and stomata density, blood glucose control, selective breeding of chickens with antibiotics and the carbon cycle, and human reproduction. Chemistry: nitrogen and air, the Periodic Table and bonding, the sodium thiosulfate rate experiment, and reactions of ethene. Physics: motion and forces, waves and a lens ray diagram, resistance and circuits, and nuclear physics and space.

How many marks is 0654/42 and how long is it? +

It is out of 120 marks and lasts 2 hours. Biology (Questions 1 to 4), chemistry (5 to 8) and physics (9 to 12) are worth 40 marks each, and no single question is worth more than 11.

What was the answer to the stomata density calculation in 0654/42? +

The circle has a diameter of 0.45 mm, so the radius is 0.225 mm and the area is 3.14 × 0.225² = 0.159 mm². Ten stomata divided by 0.159 mm² gives 63 stomata per mm², worth 2 marks.

How long did the radio wave take to travel from the Moon to the Earth in 0654/42? +

First find the orbit radius from v = 2πr ÷ T, with T = 27 days in seconds: r is about 3.8 × 10⁸ m. Then t = d ÷ v = 3.8 × 10⁸ ÷ 3.0 × 10⁸ = 1.3 s (1.27 s). It was worth 3 marks.

Is 0654/42 the Core or Extended paper? +

Extended. Paper 4 is the Extended theory paper, sat alongside Paper 2 (Extended multiple choice) and either Paper 5 or Paper 6. Core candidates sit Paper 3 instead.

Where can I download 0654/42 May/June 2026 and its mark scheme? +

Both are free to download and print on the Tutopiya Learning Portal, on the Cambridge IGCSE Co-ordinated Sciences 0654 past papers page.

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